web-animations.js

/**
 * Copyright 2012 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

(function() {
'use strict';

var ASSERT_ENABLED = false;
var SVG_NS = 'http://www.w3.org/2000/svg';

function assert(check, message) {
  console.assert(ASSERT_ENABLED,
      'assert should not be called when ASSERT_ENABLED is false');
  console.assert(check, message);
  // Some implementations of console.assert don't actually throw
  if (!check) { throw message; }
}

function detectFeatures() {
  var el = createDummyElement();
  el.style.cssText = 'width: calc(0px);' +
                     'width: -webkit-calc(0px);';
  var calcFunction = el.style.width.split('(')[0];
  function detectProperty(candidateProperties) {
    return [].filter.call(candidateProperties, function(property) {
      return property in el.style;
    })[0];
  }
  var transformProperty = detectProperty([
    'transform',
    'webkitTransform',
    'msTransform']);
  var perspectiveProperty = detectProperty([
    'perspective',
    'webkitPerspective',
    'msPerspective']);
  return {
    calcFunction: calcFunction,
    transformProperty: transformProperty,
    transformOriginProperty: transformProperty + 'Origin',
    perspectiveProperty: perspectiveProperty,
    perspectiveOriginProperty: perspectiveProperty + 'Origin'
  };
}
var features = detectFeatures();

function prefixProperty(property) {
  switch (property) {
    case 'transform':
      return features.transformProperty;
    case 'transformOrigin':
      return features.transformOriginProperty;
    case 'perspective':
      return features.perspectiveProperty;
    case 'perspectiveOrigin':
      return features.perspectiveOriginProperty;
    default:
      return property;
  }
}

function createDummyElement() {
  return document.documentElement.namespaceURI == SVG_NS ?
         document.createElementNS(SVG_NS, 'g') :
         document.createElement('div');
}

var constructorToken = {};
var deprecationsSilenced = {};

var createObject = function(proto, obj) {
  var newObject = Object.create(proto);
  Object.getOwnPropertyNames(obj).forEach(function(name) {
    Object.defineProperty(
        newObject, name, Object.getOwnPropertyDescriptor(obj, name));
  });
  return newObject;
};

var abstractMethod = function() {
  throw 'Abstract method not implemented.';
};

var deprecated = function(name, deprecationDate, advice, plural) {
  if (deprecationsSilenced[name]) {
    return;
  }
  var auxVerb = plural ? 'are' : 'is';
  var today = new Date();
  var cutoffDate = new Date(deprecationDate);
  cutoffDate.setMonth(cutoffDate.getMonth() + 3); // 3 months grace period

  if (today < cutoffDate) {
    console.warn('Web Animations: ' + name +
        ' ' + auxVerb + ' deprecated and will stop working on ' +
        cutoffDate.toDateString() + '. ' + advice);
    deprecationsSilenced[name] = true;
  } else {
    throw new Error(name + ' ' + auxVerb + ' no longer supported. ' + advice);
  }
};

var defineDeprecatedProperty = function(object, property, getFunc, setFunc) {
  var descriptor = {
    get: getFunc,
    configurable: true
  };
  if (setFunc) {
    descriptor.set = setFunc;
  }
  Object.defineProperty(object, property, descriptor);
};

var IndexSizeError = function(message) {
  Error.call(this);
  this.name = 'IndexSizeError';
  this.message = message;
};

IndexSizeError.prototype = Object.create(Error.prototype);



/** @constructor */
var TimingDict = function(timingInput) {
  if (typeof timingInput === 'object') {
    for (var k in timingInput) {
      if (k in TimingDict.prototype) {
        this[k] = timingInput[k];
      }
    }
  } else if (isDefinedAndNotNull(timingInput)) {
    this.duration = Number(timingInput);
  }
};

TimingDict.prototype = {
  delay: 0,
  endDelay: 0,
  fill: 'auto',
  iterationStart: 0,
  iterations: 1,
  duration: 'auto',
  playbackRate: 1,
  direction: 'normal',
  easing: 'linear'
};



/** @constructor */
var Timing = function(token, timingInput, changeHandler) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  this._dict = new TimingDict(timingInput);
  this._changeHandler = changeHandler;
};

Timing.prototype = {
  _timingFunction: function(timedItem) {
    var timingFunction = TimingFunction.createFromString(
        this.easing, timedItem);
    this._timingFunction = function() {
      return timingFunction;
    };
    return timingFunction;
  },
  _invalidateTimingFunction: function() {
    delete this._timingFunction;
  },
  _iterations: function() {
    var value = this._dict.iterations;
    return value < 0 ? 1 : value;
  },
  _duration: function() {
    var value = this._dict.duration;
    return typeof value === 'number' ? value : 'auto';
  },
  _clone: function() {
    return new Timing(
        constructorToken, this._dict, this._updateInternalState.bind(this));
  }
};

// Configures an accessor descriptor for use with Object.defineProperty() to
// allow the property to be changed and enumerated, to match __defineGetter__()
// and __defineSetter__().
var configureDescriptor = function(descriptor) {
  descriptor.configurable = true;
  descriptor.enumerable = true;
  return descriptor;
};

Timing._defineProperty = function(prop) {
  Object.defineProperty(Timing.prototype, prop, configureDescriptor({
    get: function() {
      return this._dict[prop];
    },
    set: function(value) {
      if (isDefinedAndNotNull(value)) {
        if (prop == 'duration' && value == 'auto') {
          // duration is not always a number
        } else if (['delay', 'endDelay', 'iterationStart', 'iterations',
                    'duration', 'playbackRate'].indexOf(prop) >= 0) {
          value = Number(value);
        }
        this._dict[prop] = value;
      } else {
        delete this._dict[prop];
      }
      // FIXME: probably need to implement specialized handling parsing
      // for each property
      if (prop === 'easing') {
        // Cached timing function may be invalid now.
        this._invalidateTimingFunction();
      }
      this._changeHandler();
    }
  }));
};

for (var prop in TimingDict.prototype) {
  Timing._defineProperty(prop);
}

var isDefined = function(val) {
  return typeof val !== 'undefined';
};

var isDefinedAndNotNull = function(val) {
  return isDefined(val) && (val !== null);
};



/** @constructor */
var AnimationTimeline = function(token) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  // TODO: This will probably need to change.
  this._startTime = documentTimeZeroAsClockTime;
};

AnimationTimeline.prototype = {
  get currentTime() {
    if (this._startTime === undefined) {
      this._startTime = documentTimeZeroAsClockTime;
      if (this._startTime === undefined) {
        return null;
      }
    }
    return relativeTime(cachedClockTime(), this._startTime);
  },
  get effectiveCurrentTime() {
    return this.currentTime || 0;
  },
  play: function(source) {
    return new AnimationPlayer(constructorToken, source, this);
  },
  getCurrentPlayers: function() {
    return PLAYERS.filter(function(player) {
      return !player._isPastEndOfActiveInterval();
    });
  },
  toTimelineTime: function(otherTime, other) {
    if ((this.currentTime === null) || (other.currentTime === null)) {
      return null;
    } else {
      return otherTime + other._startTime - this._startTime;
    }
  },
  _pauseAnimationsForTesting: function(pauseAt) {
    PLAYERS.forEach(function(player) {
      player.pause();
      player.currentTime = pauseAt;
    });

    this._freezeClockForTesting(pauseAt);
  },
  _freezeClockForTesting: function(pauseAt) {
    delete this.currentTime;
    Object.defineProperty(this, 'currentTime', {
      configurable: true,
      enumerable: true,
      get: function() {
        return pauseAt;
      }
    });
  }
};

// TODO: Remove dead players from here?
var PLAYERS = [];
var playersAreSorted = false;
var playerSequenceNumber = 0;

// Methods for event target objects.
var initializeEventTarget = function(eventTarget) {
  eventTarget._handlers = {};
  eventTarget._onHandlers = {};
};
var setOnEventHandler = function(eventTarget, type, handler) {
  if (typeof handler === 'function') {
    eventTarget._onHandlers[type] = {
      callback: handler,
      index: (eventTarget._handlers[type] || []).length
    };
  } else {
    eventTarget._onHandlers[type] = null;
  }
};
var getOnEventHandler = function(eventTarget, type) {
  if (isDefinedAndNotNull(eventTarget._onHandlers[type])) {
    return eventTarget._onHandlers[type].callback;
  }
  return null;
};
var addEventHandler = function(eventTarget, type, handler) {
  if (typeof handler !== 'function') {
    return;
  }
  if (!isDefinedAndNotNull(eventTarget._handlers[type])) {
    eventTarget._handlers[type] = [];
  } else if (eventTarget._handlers[type].indexOf(handler) !== -1) {
    return;
  }
  eventTarget._handlers[type].push(handler);
};
var removeEventHandler = function(eventTarget, type, handler) {
  if (!eventTarget._handlers[type]) {
    return;
  }
  var index = eventTarget._handlers[type].indexOf(handler);
  if (index === -1) {
    return;
  }
  eventTarget._handlers[type].splice(index, 1);
  if (isDefinedAndNotNull(eventTarget._onHandlers[type]) &&
      (index < eventTarget._onHandlers[type].index)) {
    eventTarget._onHandlers[type].index -= 1;
  }
};
var hasEventHandlersForEvent = function(eventTarget, type) {
  return (isDefinedAndNotNull(eventTarget._handlers[type]) &&
      eventTarget._handlers[type].length > 0) ||
      isDefinedAndNotNull(eventTarget._onHandlers[type]);
};
var callEventHandlers = function(eventTarget, type, event) {
  var callbackList;
  if (isDefinedAndNotNull(eventTarget._handlers[type])) {
    callbackList = eventTarget._handlers[type].slice();
  } else {
    callbackList = [];
  }
  if (isDefinedAndNotNull(eventTarget._onHandlers[type])) {
    callbackList.splice(eventTarget._onHandlers[type].index, 0,
        eventTarget._onHandlers[type].callback);
  }
  setTimeout(function() {
    for (var i = 0; i < callbackList.length; i++) {
      callbackList[i].call(eventTarget, event);
    }
  }, 0);
};
var createEventPrototype = function() {
  var prototype = Object.create(window.Event.prototype, {
    type: { get: function() { return this._type; } },
    target: { get: function() { return this._target; } },
    currentTarget: { get: function() { return this._target; } },
    eventPhase: { get: function() { return this._eventPhase; } },
    bubbles: { get: function() { return false; } },
    cancelable: { get: function() { return false; } },
    timeStamp: { get: function() { return this._timeStamp; } },
    defaultPrevented: { get: function() { return false; } }
  });
  prototype._type = '';
  prototype._target = null;
  prototype._eventPhase = Event.NONE;
  prototype._timeStamp = 0;
  prototype._initialize = function(target) {
    this._target = target;
    this._eventPhase = Event.AT_TARGET;
    this._timeStamp = cachedClockTime();
  };
  return prototype;
};



/** @constructor */
var AnimationPlayer = function(token, source, timeline) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  enterModifyCurrentAnimationState();
  try {
    this._registeredOnTimeline = false;
    this._sequenceNumber = playerSequenceNumber++;
    this._timeline = timeline;
    this._startTime =
        this.timeline.currentTime === null ? 0 : this.timeline.currentTime;
    this._storedTimeLag = 0.0;
    this._pausedState = false;
    this._holdTime = null;
    this._previousCurrentTime = null;
    this._playbackRate = 1.0;
    this._hasTicked = false;

    this.source = source;
    this._lastCurrentTime = undefined;
    this._finishedFlag = false;
    initializeEventTarget(this);

    playersAreSorted = false;
    maybeRestartAnimation();
  } finally {
    exitModifyCurrentAnimationState(ensureRetickBeforeGetComputedStyle);
  }
};

AnimationPlayer.prototype = {
  set source(source) {
    enterModifyCurrentAnimationState();
    try {
      if (isDefinedAndNotNull(this.source)) {
        // To prevent infinite recursion.
        var oldTimedItem = this.source;
        this._source = null;
        oldTimedItem._attach(null);
      }
      this._source = source;
      if (isDefinedAndNotNull(this.source)) {
        this.source._attach(this);
        this._update();
        maybeRestartAnimation();
      }
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get source() {
    return this._source;
  },
  // This is the effective current time.
  set currentTime(currentTime) {
    enterModifyCurrentAnimationState();
    try {
      this._currentTime = currentTime;
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get currentTime() {
    return this._currentTime;
  },
  set _currentTime(seekTime) {
    // If we are paused or seeking to a time where limiting applies (i.e. beyond
    // the end in the current direction), update the hold time.
    var sourceContentEnd = this.source ? this.source.endTime : 0;
    if (this.paused ||
        (this.playbackRate > 0 && seekTime >= sourceContentEnd) ||
        (this.playbackRate < 0 && seekTime <= 0)) {
      this._holdTime = seekTime;
    // Otherwise, clear the hold time (it may been set by previously seeking to
    // a limited time) and update the time lag.
    } else {
      this._holdTime = null;
      this._storedTimeLag = (this.timeline.effectiveCurrentTime -
          this.startTime) * this.playbackRate - seekTime;
    }
    this._update();
    maybeRestartAnimation();
  },
  get _currentTime() {
    this._previousCurrentTime = (this.timeline.effectiveCurrentTime -
        this.startTime) * this.playbackRate - this.timeLag;
    return this._previousCurrentTime;
  },
  get _unlimitedCurrentTime() {
    return (this.timeline.effectiveCurrentTime - this.startTime) *
        this.playbackRate - this._storedTimeLag;
  },
  get timeLag() {
    if (this.paused) {
      return this._pauseTimeLag;
    }

    // Apply limiting at start of interval when playing in reverse
    if (this.playbackRate < 0 && this._unlimitedCurrentTime <= 0) {
      if (this._holdTime === null) {
        this._holdTime = Math.min(this._previousCurrentTime, 0);
      }
      return this._pauseTimeLag;
    }

    // Apply limiting at end of interval when playing forwards
    var sourceContentEnd = this.source ? this.source.endTime : 0;
    if (this.playbackRate > 0 &&
        this._unlimitedCurrentTime >= sourceContentEnd) {
      if (this._holdTime === null) {
        this._holdTime = Math.max(this._previousCurrentTime, sourceContentEnd);
      }
      return this._pauseTimeLag;
    }

    // Finished limiting so store pause time lag
    if (this._holdTime !== null) {
      this._storedTimeLag = this._pauseTimeLag;
      this._holdTime = null;
    }

    return this._storedTimeLag;
  },
  get _pauseTimeLag() {
    return ((this.timeline.currentTime || 0) - this.startTime) *
        this.playbackRate - this._holdTime;
  },
  set startTime(startTime) {
    enterModifyCurrentAnimationState();
    try {
      // This seeks by updating _startTime and hence the currentTime. It does
      // not affect _storedTimeLag.
      this._startTime = startTime;
      this._holdTime = null;
      playersAreSorted = false;
      this._update();
      maybeRestartAnimation();
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get startTime() {
    return this._startTime;
  },
  set _paused(isPaused) {
    if (isPaused === this._pausedState) {
      return;
    }
    if (this._pausedState) {
      this._storedTimeLag = this.timeLag;
      this._holdTime = null;
      maybeRestartAnimation();
    } else {
      this._holdTime = this.currentTime;
    }
    this._pausedState = isPaused;
  },
  get paused() {
    return this._pausedState;
  },
  get timeline() {
    return this._timeline;
  },
  set playbackRate(playbackRate) {
    enterModifyCurrentAnimationState();
    try {
      var cachedCurrentTime = this.currentTime;
      // This will impact currentTime, so perform a compensatory seek.
      this._playbackRate = playbackRate;
      this.currentTime = cachedCurrentTime;
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get playbackRate() {
    return this._playbackRate;
  },
  get finished() {
    return this._isLimited;
  },
  get _isLimited() {
    var sourceEnd = this.source ? this.source.endTime : 0;
    return ((this.playbackRate > 0 && this.currentTime >= sourceEnd) ||
        (this.playbackRate < 0 && this.currentTime <= 0));
  },
  cancel: function() {
    this.source = null;
  },
  finish: function() {
    if (this.playbackRate < 0) {
      this.currentTime = 0;
    } else if (this.playbackRate > 0) {
      var sourceEndTime = this.source ? this.source.endTime : 0;
      if (sourceEndTime === Infinity) {
        throw new Error('InvalidStateError');
      }
      this.currentTime = sourceEndTime;
    }
  },
  play: function() {
    this._paused = false;
    if (!this.source) {
      return;
    }
    if (this.playbackRate > 0 &&
        (this.currentTime < 0 ||
         this.currentTime >= this.source.endTime)) {
      this.currentTime = 0;
    } else if (this.playbackRate < 0 &&
        (this.currentTime <= 0 ||
        this.currentTime > this.source.endTime)) {
      this.currentTime = this.source.endTime;
    }
  },
  pause: function() {
    this._paused = true;
  },
  reverse: function() {
    if (this.playbackRate === 0) {
      return;
    }
    if (this.source) {
      if (this.playbackRate > 0 && this.currentTime >= this.source.endTime) {
        this.currentTime = this.source.endTime;
      } else if (this.playbackRate < 0 && this.currentTime < 0) {
        this.currentTime = 0;
      }
    }
    this.playbackRate = -this.playbackRate;
    this._paused = false;
  },
  _update: function() {
    if (this.source !== null) {
      this.source._updateInheritedTime(
          this.timeline.currentTime === null ? null : this._currentTime);
      this._registerOnTimeline();
    }
  },
  _hasFutureAnimation: function() {
    return this.source === null || this.playbackRate === 0 ||
        this.source._hasFutureAnimation(this.playbackRate > 0);
  },
  _isPastEndOfActiveInterval: function() {
    return this.source === null ||
        this.source._isPastEndOfActiveInterval();
  },
  _isCurrent: function() {
    return this.source && this.source._isCurrent();
  },
  _hasFutureEffect: function() {
    return this.source && this.source._hasFutureEffect();
  },
  _getLeafItemsInEffect: function(items) {
    if (this.source) {
      this.source._getLeafItemsInEffect(items);
    }
  },
  _isTargetingElement: function(element) {
    return this.source && this.source._isTargetingElement(element);
  },
  _getAnimationsTargetingElement: function(element, animations) {
    if (this.source) {
      this.source._getAnimationsTargetingElement(element, animations);
    }
  },
  set onfinish(handler) {
    return setOnEventHandler(this, 'finish', handler);
  },
  get onfinish() {
    return getOnEventHandler(this, 'finish');
  },
  addEventListener: function(type, handler) {
    if (type === 'finish') {
      addEventHandler(this, type, handler);
    }
  },
  removeEventListener: function(type, handler) {
    if (type === 'finish') {
      removeEventHandler(this, type, handler);
    }
  },
  _generateEvents: function() {
    if (!this._finishedFlag && this.finished &&
        hasEventHandlersForEvent(this, 'finish')) {
      var event = new AnimationPlayerEvent('finish', {
        currentTime: this.currentTime,
        timelineTime: this.timeline.currentTime
      });
      event._initialize(this);
      callEventHandlers(this, 'finish', event);
    }
    this._finishedFlag = this.finished;

    // The following code is for deprecated TimedItem event handling and should
    // be removed once we stop supporting it.
    if (!isDefinedAndNotNull(this._lastCurrentTime)) {
      this._lastCurrentTime = 0;
    }

    this._lastCurrentTime = this._unlimitedCurrentTime;
  },
  _registerOnTimeline: function() {
    if (!this._registeredOnTimeline) {
      PLAYERS.push(this);
      this._registeredOnTimeline = true;
    }
  },
  _deregisterFromTimeline: function() {
    PLAYERS.splice(PLAYERS.indexOf(this), 1);
    this._registeredOnTimeline = false;
  }
};



/** @constructor */
var AnimationPlayerEvent = function(type, eventInit) {
  this._type = type;
  this.currentTime = eventInit.currentTime;
  this.timelineTime = eventInit.timelineTime;
};

AnimationPlayerEvent.prototype = createEventPrototype();



/** @constructor */
var TimedItem = function(token, timingInput) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  this.timing = new Timing(
      constructorToken, timingInput,
      this._specifiedTimingModified.bind(this));
  this._inheritedTime = null;
  this.currentIteration = null;
  this._iterationTime = null;
  this._animationTime = null;
  this._startTime = 0.0;
  this._player = null;
  this._parent = null;
  this._updateInternalState();
  this._fill = this._resolveFillMode(this.timing.fill);
  initializeEventTarget(this);
};

TimedItem.prototype = {
  // TODO: It would be good to avoid the need for this. We would need to modify
  // call sites to instead rely on a call from the parent.
  get _effectiveParentTime() {
    return this.parent !== null && this.parent._iterationTime !== null ?
        this.parent._iterationTime : 0;
  },
  get localTime() {
    return this._inheritedTime === null ?
        null : this._inheritedTime - this._startTime;
  },
  get startTime() {
    return this._startTime;
  },
  get duration() {
    var result = this.timing._duration();
    if (result === 'auto') {
      result = this._intrinsicDuration();
    }
    return result;
  },
  get activeDuration() {
    var repeatedDuration = this.duration * this.timing._iterations();
    return repeatedDuration / Math.abs(this.timing.playbackRate);
  },
  get endTime() {
    return this._startTime + this.activeDuration + this.timing.delay +
        this.timing.endDelay;
  },
  get parent() {
    return this._parent;
  },
  get previousSibling() {
    if (!this.parent) {
      return null;
    }
    var siblingIndex = this.parent.indexOf(this) - 1;
    if (siblingIndex < 0) {
      return null;
    }
    return this.parent.children[siblingIndex];
  },
  get nextSibling() {
    if (!this.parent) {
      return null;
    }
    var siblingIndex = this.parent.indexOf(this) + 1;
    if (siblingIndex >= this.parent.children.length) {
      return null;
    }
    return this.parent.children[siblingIndex];
  },
  _attach: function(player) {
    // Remove ourselves from our parent, if we have one. This also removes any
    // exsisting player.
    this._reparent(null);
    this._player = player;
  },
  // Takes care of updating the outgoing parent. This is called with a non-null
  // parent only from TimingGroup.splice(), which takes care of calling
  // TimingGroup._childrenStateModified() for the new parent.
  _reparent: function(parent) {
    if (parent === this) {
      throw new Error('parent can not be set to self!');
    }
    enterModifyCurrentAnimationState();
    try {
      if (this._player !== null) {
        this._player.source = null;
        this._player = null;
      }
      if (this.parent !== null) {
        this.remove();
      }
      this._parent = parent;
      // In the case of a AnimationSequence parent, _startTime will be updated
      // by TimingGroup.splice().
      if (this.parent === null || this.parent.type !== 'seq') {
        this._startTime =
            this._stashedStartTime === undefined ? 0.0 : this._stashedStartTime;
        this._stashedStartTime = undefined;
      }
      // In the case of the parent being non-null, _childrenStateModified() will
      // call this via _updateChildInheritedTimes().
      // TODO: Consider optimising this case by skipping this call.
      this._updateTimeMarkers();
    } finally {
      exitModifyCurrentAnimationState(
          Boolean(this.player) ? repeatLastTick : null);
    }
  },
  _intrinsicDuration: function() {
    return 0.0;
  },
  _resolveFillMode: abstractMethod,
  _updateInternalState: function() {
    this._fill = this._resolveFillMode(this.timing.fill);
    if (this.parent) {
      this.parent._childrenStateModified();
    } else if (this._player) {
      this._player._registerOnTimeline();
    }
    this._updateTimeMarkers();
  },
  _specifiedTimingModified: function() {
    enterModifyCurrentAnimationState();
    try {
      this._updateInternalState();
    } finally {
      exitModifyCurrentAnimationState(
          Boolean(this.player) ? repeatLastTick : null);
    }
  },
  // We push time down to children. We could instead have children pull from
  // above, but this is tricky because a TimedItem may use either a parent
  // TimedItem or an AnimationPlayer. This requires either logic in
  // TimedItem, or for TimedItem and AnimationPlayer to implement Timeline
  // (or an equivalent), both of which are ugly.
  _updateInheritedTime: function(inheritedTime) {
    this._inheritedTime = inheritedTime;
    this._updateTimeMarkers();
  },
  _updateAnimationTime: function() {
    if (this.localTime < this.timing.delay) {
      if (this._fill === 'backwards' ||
          this._fill === 'both') {
        this._animationTime = 0;
      } else {
        this._animationTime = null;
      }
    } else if (this.localTime <
        this.timing.delay + this.activeDuration) {
      this._animationTime = this.localTime - this.timing.delay;
    } else {
      if (this._fill === 'forwards' ||
          this._fill === 'both') {
        this._animationTime = this.activeDuration;
      } else {
        this._animationTime = null;
      }
    }
  },
  _updateIterationParamsZeroDuration: function() {
    this._iterationTime = 0;
    var isAtEndOfIterations = this.timing._iterations() !== 0 &&
        this.localTime >= this.timing.delay;
    this.currentIteration = (
        isAtEndOfIterations ?
        this._floorWithOpenClosedRange(
            this.timing.iterationStart + this.timing._iterations(),
            1.0) :
        this._floorWithClosedOpenRange(this.timing.iterationStart, 1.0));
    // Equivalent to unscaledIterationTime below.
    var unscaledFraction = (
        isAtEndOfIterations ?
        this._modulusWithOpenClosedRange(
            this.timing.iterationStart + this.timing._iterations(),
            1.0) :
        this._modulusWithClosedOpenRange(this.timing.iterationStart, 1.0));
    var timingFunction = this.timing._timingFunction(this);
    this._timeFraction = (
        this._isCurrentDirectionForwards() ?
        unscaledFraction :
        1.0 - unscaledFraction);
    ASSERT_ENABLED && assert(
        this._timeFraction >= 0.0 && this._timeFraction <= 1.0,
        'Time fraction should be in the range [0, 1]');
    if (timingFunction) {
      this._timeFraction = timingFunction.scaleTime(this._timeFraction);
    }
  },
  _getAdjustedAnimationTime: function(animationTime) {
    var startOffset =
        multiplyZeroGivesZero(this.timing.iterationStart, this.duration);
    return (this.timing.playbackRate < 0 ?
        (animationTime - this.activeDuration) : animationTime) *
        this.timing.playbackRate + startOffset;
  },
  _scaleIterationTime: function(unscaledIterationTime) {
    return this._isCurrentDirectionForwards() ?
        unscaledIterationTime :
        this.duration - unscaledIterationTime;
  },
  _updateIterationParams: function() {
    var adjustedAnimationTime =
        this._getAdjustedAnimationTime(this._animationTime);
    var repeatedDuration = this.duration * this.timing._iterations();
    var startOffset = this.timing.iterationStart * this.duration;
    var isAtEndOfIterations = (this.timing._iterations() !== 0) &&
        (adjustedAnimationTime - startOffset === repeatedDuration);
    this.currentIteration = isAtEndOfIterations ?
        this._floorWithOpenClosedRange(
            adjustedAnimationTime, this.duration) :
        this._floorWithClosedOpenRange(
            adjustedAnimationTime, this.duration);
    var unscaledIterationTime = isAtEndOfIterations ?
        this._modulusWithOpenClosedRange(
            adjustedAnimationTime, this.duration) :
        this._modulusWithClosedOpenRange(
            adjustedAnimationTime, this.duration);
    this._iterationTime = this._scaleIterationTime(unscaledIterationTime);
    if (this.duration == Infinity) {
      this._timeFraction = 0;
      return;
    }
    this._timeFraction = this._iterationTime / this.duration;
    ASSERT_ENABLED && assert(
        this._timeFraction >= 0.0 && this._timeFraction <= 1.0,
        'Time fraction should be in the range [0, 1], got ' +
        this._timeFraction + ' ' + this._iterationTime + ' ' +
        this.duration + ' ' + isAtEndOfIterations + ' ' +
        unscaledIterationTime);
    var timingFunction = this.timing._timingFunction(this);
    if (timingFunction) {
      this._timeFraction = timingFunction.scaleTime(this._timeFraction);
    }
    this._iterationTime = this._timeFraction * this.duration;
  },
  _updateTimeMarkers: function() {
    if (this.localTime === null) {
      this._animationTime = null;
      this._iterationTime = null;
      this.currentIteration = null;
      this._timeFraction = null;
      return false;
    }
    this._updateAnimationTime();
    if (this._animationTime === null) {
      this._iterationTime = null;
      this.currentIteration = null;
      this._timeFraction = null;
    } else if (this.duration === 0) {
      this._updateIterationParamsZeroDuration();
    } else {
      this._updateIterationParams();
    }
    maybeRestartAnimation();
  },
  _floorWithClosedOpenRange: function(x, range) {
    return Math.floor(x / range);
  },
  _floorWithOpenClosedRange: function(x, range) {
    return Math.ceil(x / range) - 1;
  },
  _modulusWithClosedOpenRange: function(x, range) {
    ASSERT_ENABLED && assert(
        range > 0, 'Range must be strictly positive');
    var modulus = x % range;
    var result = modulus < 0 ? modulus + range : modulus;
    ASSERT_ENABLED && assert(
        result >= 0.0 && result < range,
        'Result should be in the range [0, range)');
    return result;
  },
  _modulusWithOpenClosedRange: function(x, range) {
    var modulus = this._modulusWithClosedOpenRange(x, range);
    var result = modulus === 0 ? range : modulus;
    ASSERT_ENABLED && assert(
        result > 0.0 && result <= range,
        'Result should be in the range (0, range]');
    return result;
  },
  _isCurrentDirectionForwards: function() {
    if (this.timing.direction === 'normal') {
      return true;
    }
    if (this.timing.direction === 'reverse') {
      return false;
    }
    var d = this.currentIteration;
    if (this.timing.direction === 'alternate-reverse') {
      d += 1;
    }
    // TODO: 6.13.3 step 3. wtf?
    return d % 2 === 0;
  },
  clone: abstractMethod,
  before: function() {
    var newItems = [];
    for (var i = 0; i < arguments.length; i++) {
      newItems.push(arguments[i]);
    }
    this.parent._splice(this.parent.indexOf(this), 0, newItems);
  },
  after: function() {
    var newItems = [];
    for (var i = 0; i < arguments.length; i++) {
      newItems.push(arguments[i]);
    }
    this.parent._splice(this.parent.indexOf(this) + 1, 0, newItems);
  },
  replace: function() {
    var newItems = [];
    for (var i = 0; i < arguments.length; i++) {
      newItems.push(arguments[i]);
    }
    this.parent._splice(this.parent.indexOf(this), 1, newItems);
  },
  remove: function() {
    this.parent._splice(this.parent.indexOf(this), 1);
  },
  // Gets the leaf TimedItems currently in effect. Note that this is a superset
  // of the leaf TimedItems in their active interval, as a TimedItem can have an
  // effect outside its active interval due to fill.
  _getLeafItemsInEffect: function(items) {
    if (this._timeFraction !== null) {
      this._getLeafItemsInEffectImpl(items);
    }
  },
  _getLeafItemsInEffectImpl: abstractMethod,
  _hasFutureAnimation: function(timeDirectionForwards) {
    return timeDirectionForwards ? this._inheritedTime < this.endTime :
        this._inheritedTime > this.startTime;
  },
  _isPastEndOfActiveInterval: function() {
    return this._inheritedTime >= this.endTime;
  },
  get player() {
    return this.parent === null ?
        this._player : this.parent.player;
  },
  _isCurrent: function() {
    return !this._isPastEndOfActiveInterval() ||
           (this.parent !== null && this.parent._isCurrent());
  },
  _isTargetingElement: abstractMethod,
  _getAnimationsTargetingElement: abstractMethod,
  _netEffectivePlaybackRate: function() {
    var effectivePlaybackRate = this._isCurrentDirectionForwards() ?
        this.timing.playbackRate : -this.timing.playbackRate;
    return this.parent === null ? effectivePlaybackRate :
        effectivePlaybackRate * this.parent._netEffectivePlaybackRate();
  },
  // Note that this restriction is currently incomplete - for example,
  // Animations which are playing forwards and have a fill of backwards
  // are not in effect unless current.
  // TODO: Complete this restriction.
  _hasFutureEffect: function() {
    return this._isCurrent() || this._fill !== 'none';
  },
  _toSubRanges: function(fromTime, toTime, iterationTimes) {
    if (fromTime > toTime) {
      var revRanges = this._toSubRanges(toTime, fromTime, iterationTimes);
      revRanges.ranges.forEach(function(a) { a.reverse(); });
      revRanges.ranges.reverse();
      revRanges.start = iterationTimes.length - revRanges.start - 1;
      revRanges.delta = -1;
      return revRanges;
    }
    var skipped = 0;
    // TODO: this should be calculatable. This would be more efficient
    // than searching through the list.
    while (iterationTimes[skipped] < fromTime) {
      skipped++;
    }
    var currentStart = fromTime;
    var ranges = [];
    for (var i = skipped; i < iterationTimes.length; i++) {
      if (iterationTimes[i] < toTime) {
        ranges.push([currentStart, iterationTimes[i]]);
        currentStart = iterationTimes[i];
      } else {
        ranges.push([currentStart, toTime]);
        return {start: skipped, delta: 1, ranges: ranges};
      }
    }
    ranges.push([currentStart, toTime]);
    return {start: skipped, delta: 1, ranges: ranges};
  }
};

var TimingEvent = function(
    token, target, type, localTime, timelineTime, iterationIndex, seeked) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  this._initialize(target);
  this._type = type;
  this.localTime = localTime;
  this.timelineTime = timelineTime;
  this.iterationIndex = iterationIndex;
  this.seeked = seeked ? true : false;
};

TimingEvent.prototype = createEventPrototype();

var isEffectCallback = function(animationEffect) {
  return typeof animationEffect === 'function';
};

var interpretAnimationEffect = function(animationEffect) {
  if (animationEffect instanceof AnimationEffect ||
      isEffectCallback(animationEffect)) {
    return animationEffect;
  } else if (isDefinedAndNotNull(animationEffect) &&
      typeof animationEffect === 'object') {
    // The spec requires animationEffect to be an instance of
    // OneOrMoreKeyframes, but this type is just a dictionary or a list of
    // dictionaries, so the best we can do is test for an object.
    return new KeyframeEffect(animationEffect);
  }
  return null;
};

var cloneAnimationEffect = function(animationEffect) {
  if (animationEffect instanceof AnimationEffect) {
    return animationEffect.clone();
  } else if (isEffectCallback(animationEffect)) {
    return animationEffect;
  } else {
    return null;
  }
};



/** @constructor */
var Animation = function(target, animationEffect, timingInput) {
  enterModifyCurrentAnimationState();
  try {
    TimedItem.call(this, constructorToken, timingInput);
    this.effect = interpretAnimationEffect(animationEffect);
    this._target = target;
  } finally {
    exitModifyCurrentAnimationState(null);
  }
};

Animation.prototype = createObject(TimedItem.prototype, {
  _resolveFillMode: function(fillMode) {
    return fillMode === 'auto' ? 'none' : fillMode;
  },
  _sample: function() {
    if (isDefinedAndNotNull(this.effect) &&
        !(this.target instanceof PseudoElementReference)) {
      if (isEffectCallback(this.effect)) {
        this.effect(this._timeFraction, this.target, this);
      } else {
        this.effect._sample(this._timeFraction, this.currentIteration,
            this.target, this.underlyingValue);
      }
    }
  },
  _getLeafItemsInEffectImpl: function(items) {
    items.push(this);
  },
  _isTargetingElement: function(element) {
    return element === this.target;
  },
  _getAnimationsTargetingElement: function(element, animations) {
    if (this._isTargetingElement(element)) {
      animations.push(this);
    }
  },
  get target() {
    return this._target;
  },
  set effect(effect) {
    enterModifyCurrentAnimationState();
    try {
      this._effect = effect;
      this.timing._invalidateTimingFunction();
    } finally {
      exitModifyCurrentAnimationState(
          Boolean(this.player) ? repeatLastTick : null);
    }
  },
  get effect() {
    return this._effect;
  },
  clone: function() {
    return new Animation(this.target,
        cloneAnimationEffect(this.effect), this.timing._dict);
  },
  toString: function() {
    var effectString = '<none>';
    if (this.effect instanceof AnimationEffect) {
      effectString = this.effect.toString();
    } else if (isEffectCallback(this.effect)) {
      effectString = 'Effect callback';
    }
    return 'Animation ' + this.startTime + '-' + this.endTime + ' (' +
        this.localTime + ') ' + effectString;
  }
});

function throwNewHierarchyRequestError() {
  var element = document.createElement('span');
  element.appendChild(element);
}



/** @constructor */
var TimedItemList = function(token, children) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  this._children = children;
  this._getters = 0;
  this._ensureGetters();
};

TimedItemList.prototype = {
  get length() {
    return this._children.length;
  },
  _ensureGetters: function() {
    while (this._getters < this._children.length) {
      this._ensureGetter(this._getters++);
    }
  },
  _ensureGetter: function(i) {
    Object.defineProperty(this, i, {
      get: function() {
        return this._children[i];
      }
    });
  }
};



/** @constructor */
var TimingGroup = function(token, type, children, timing) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
  // Take a copy of the children array, as it could be modified as a side-effect
  // of creating this object. See
  // https://github.com/web-animations/web-animations-js/issues/65 for details.
  var childrenCopy = (children && Array.isArray(children)) ?
      children.slice() : [];
  // used by TimedItem via _intrinsicDuration(), so needs to be set before
  // initializing super.
  this.type = type || 'par';
  this._children = [];
  this._cachedTimedItemList = null;
  this._cachedIntrinsicDuration = null;
  TimedItem.call(this, constructorToken, timing);
  // We add children after setting the parent. This means that if an ancestor
  // (including the parent) is specified as a child, it will be removed from our
  // ancestors and used as a child,
  this.append.apply(this, childrenCopy);
};

TimingGroup.prototype = createObject(TimedItem.prototype, {
  _resolveFillMode: function(fillMode) {
    return fillMode === 'auto' ? 'both' : fillMode;
  },
  _childrenStateModified: function() {
    // See _updateChildStartTimes().
    this._isInChildrenStateModified = true;
    if (this._cachedTimedItemList) {
      this._cachedTimedItemList._ensureGetters();
    }
    this._cachedIntrinsicDuration = null;

    // We need to walk up and down the tree to re-layout. endTime and the
    // various durations (which are all calculated lazily) are the only
    // properties of a TimedItem which can affect the layout of its ancestors.
    // So it should be sufficient to simply update start times and time markers
    // on the way down.

    // This calls up to our parent, then calls _updateTimeMarkers().
    this._updateInternalState();
    this._updateChildInheritedTimes();

    // Update child start times before walking down.
    this._updateChildStartTimes();

    this._isInChildrenStateModified = false;
  },
  _updateInheritedTime: function(inheritedTime) {
    this._inheritedTime = inheritedTime;
    this._updateTimeMarkers();
    this._updateChildInheritedTimes();
  },
  _updateChildInheritedTimes: function() {
    for (var i = 0; i < this._children.length; i++) {
      var child = this._children[i];
      child._updateInheritedTime(this._iterationTime);
    }
  },
  _updateChildStartTimes: function() {
    if (this.type === 'seq') {
      var cumulativeStartTime = 0;
      for (var i = 0; i < this._children.length; i++) {
        var child = this._children[i];
        if (child._stashedStartTime === undefined) {
          child._stashedStartTime = child._startTime;
        }
        child._startTime = cumulativeStartTime;
        // Avoid updating the child's inherited time and time markers if this is
        // about to be done in the down phase of _childrenStateModified().
        if (!child._isInChildrenStateModified) {
          // This calls _updateTimeMarkers() on the child.
          child._updateInheritedTime(this._iterationTime);
        }
        cumulativeStartTime += Math.max(0, child.timing.delay +
            child.activeDuration + child.timing.endDelay);
      }
    }
  },
  get children() {
    if (!this._cachedTimedItemList) {
      this._cachedTimedItemList = new TimedItemList(
          constructorToken, this._children);
    }
    return this._cachedTimedItemList;
  },
  get firstChild() {
    return this._children[0];
  },
  get lastChild() {
    return this._children[this.children.length - 1];
  },
  _intrinsicDuration: function() {
    if (!isDefinedAndNotNull(this._cachedIntrinsicDuration)) {
      if (this.type === 'par') {
        var dur = Math.max.apply(undefined, this._children.map(function(a) {
          return a.endTime;
        }));
        this._cachedIntrinsicDuration = Math.max(0, dur);
      } else if (this.type === 'seq') {
        var result = 0;
        this._children.forEach(function(a) {
          result += a.activeDuration + a.timing.delay + a.timing.endDelay;
        });
        this._cachedIntrinsicDuration = result;
      } else {
        throw 'Unsupported type ' + this.type;
      }
    }
    return this._cachedIntrinsicDuration;
  },
  _getLeafItemsInEffectImpl: function(items) {
    for (var i = 0; i < this._children.length; i++) {
      this._children[i]._getLeafItemsInEffect(items);
    }
  },
  clone: function() {
    var children = [];
    this._children.forEach(function(child) {
      children.push(child.clone());
    });
    return this.type === 'par' ?
        new AnimationGroup(children, this.timing._dict) :
        new AnimationSequence(children, this.timing._dict);
  },
  clear: function() {
    this._splice(0, this._children.length);
  },
  append: function() {
    var newItems = [];
    for (var i = 0; i < arguments.length; i++) {
      newItems.push(arguments[i]);
    }
    this._splice(this._children.length, 0, newItems);
  },
  prepend: function() {
    var newItems = [];
    for (var i = 0; i < arguments.length; i++) {
      newItems.push(arguments[i]);
    }
    this._splice(0, 0, newItems);
  },
  _addInternal: function(child) {
    this._children.push(child);
    this._childrenStateModified();
  },
  indexOf: function(item) {
    return this._children.indexOf(item);
  },
  _splice: function(start, deleteCount, newItems) {
    enterModifyCurrentAnimationState();
    try {
      var args = arguments;
      if (args.length === 3) {
        args = [start, deleteCount].concat(newItems);
      }
      for (var i = 2; i < args.length; i++) {
        var newChild = args[i];
        if (this._isInclusiveAncestor(newChild)) {
          throwNewHierarchyRequestError();
        }
        newChild._reparent(this);
      }
      var result = Array.prototype.splice.apply(this._children, args);
      for (var i = 0; i < result.length; i++) {
        result[i]._parent = null;
      }
      this._childrenStateModified();
      return result;
    } finally {
      exitModifyCurrentAnimationState(
          Boolean(this.player) ? repeatLastTick : null);
    }
  },
  _isInclusiveAncestor: function(item) {
    for (var ancestor = this; ancestor !== null; ancestor = ancestor.parent) {
      if (ancestor === item) {
        return true;
      }
    }
    return false;
  },
  _isTargetingElement: function(element) {
    return this._children.some(function(child) {
      return child._isTargetingElement(element);
    });
  },
  _getAnimationsTargetingElement: function(element, animations) {
    this._children.map(function(child) {
      return child._getAnimationsTargetingElement(element, animations);
    });
  },
  toString: function() {
    return this.type + ' ' + this.startTime + '-' + this.endTime + ' (' +
        this.localTime + ') ' + ' [' +
        this._children.map(function(a) { return a.toString(); }) + ']';
  }
});



/** @constructor */
var AnimationGroup = function(children, timing, parent) {
  TimingGroup.call(this, constructorToken, 'par', children, timing, parent);
};

AnimationGroup.prototype = Object.create(TimingGroup.prototype);



/** @constructor */
var AnimationSequence = function(children, timing, parent) {
  TimingGroup.call(this, constructorToken, 'seq', children, timing, parent);
};

AnimationSequence.prototype = Object.create(TimingGroup.prototype);



/** @constructor */
var PseudoElementReference = function(element, pseudoElement) {
  this.element = element;
  this.pseudoElement = pseudoElement;
  console.warn('PseudoElementReference is not supported.');
};



/** @constructor */
var MediaReference = function(mediaElement, timing, parent, delta) {
  TimedItem.call(this, constructorToken, timing, parent);
  this._media = mediaElement;

  // We can never be sure when _updateInheritedTime() is going to be called
  // next, due to skipped frames or the player being seeked. Plus the media
  // element's currentTime may drift from our iterationTime. So if a media
  // element has loop set, we can't be sure that we'll stop it before it wraps.
  // For this reason, we simply disable looping.
  // TODO: Maybe we should let it loop if our duration exceeds it's
  // length?
  this._media.loop = false;

  // If the media element has a media controller, we detach it. This mirrors the
  // behaviour when re-parenting a TimedItem, or attaching one to an
  // AnimationPlayer.
  // TODO: It would be neater to assign to MediaElement.controller, but this was
  // broken in Chrome until recently. See crbug.com/226270.
  this._media.mediaGroup = '';

  this._delta = delta;
};

MediaReference.prototype = createObject(TimedItem.prototype, {
  _resolveFillMode: function(fillMode) {
    // TODO: Fill modes for MediaReferences are still undecided. The spec is not
    // clear what 'auto' should mean for TimedItems other than Animations and
    // groups.
    return fillMode === 'auto' ? 'none' : fillMode;
  },
  _intrinsicDuration: function() {
    // TODO: This should probably default to zero. But doing so means that as
    // soon as our inheritedTime is zero, the polyfill deems the animation to be
    // done and stops ticking, so we don't get any further calls to
    // _updateInheritedTime(). One way around this would be to modify
    // TimedItem._isPastEndOfActiveInterval() to recurse down the tree, then we
    // could override it here.
    return isNaN(this._media.duration) ?
        Infinity : this._media.duration / this._media.defaultPlaybackRate;
  },
  _unscaledMediaCurrentTime: function() {
    return this._media.currentTime / this._media.defaultPlaybackRate;
  },
  _getLeafItemsInEffectImpl: function(items) {
    items.push(this);
  },
  _ensurePlaying: function() {
    // The media element is paused when created.
    if (this._media.paused) {
      this._media.play();
    }
  },
  _ensurePaused: function() {
    if (!this._media.paused) {
      this._media.pause();
    }
  },
  _isSeekableUnscaledTime: function(time) {
    var seekTime = time * this._media.defaultPlaybackRate;
    var ranges = this._media.seekable;
    for (var i = 0; i < ranges.length; i++) {
      if (seekTime >= ranges.start(i) && seekTime <= ranges.end(i)) {
        return true;
      }
    }
    return false;
  },
  // Note that a media element's timeline may not start at zero, although its
  // duration is always the timeline time at the end point. This means that an
  // element's duration isn't always it's length and not all values of the
  // timline are seekable. Furthermore, some types of media further limit the
  // range of seekable timeline times. For this reason, we always map an
  // iteration to the range [0, duration] and simply seek to the nearest
  // seekable time.
  _ensureIsAtUnscaledTime: function(time) {
    if (this._unscaledMediaCurrentTime() !== time) {
      this._media.currentTime = time * this._media.defaultPlaybackRate;
    }
  },
  // This is called by the polyfill on each tick when our AnimationPlayer's tree
  // is active.
  _updateInheritedTime: function(inheritedTime) {
    this._inheritedTime = inheritedTime;
    this._updateTimeMarkers();

    // The polyfill uses a sampling model whereby time values are propagated
    // down the tree at each sample. However, for the media item, we need to use
    // play() and pause().

    // Handle the case of being outside our effect interval.
    if (this._iterationTime === null) {
      this._ensureIsAtUnscaledTime(0);
      this._ensurePaused();
      return;
    }

    if (this._iterationTime >= this._intrinsicDuration()) {
      // Our iteration time exceeds the media element's duration, so just make
      // sure the media element is at the end. It will stop automatically, but
      // that could take some time if the seek below is significant, so force
      // it.
      this._ensureIsAtUnscaledTime(this._intrinsicDuration());
      this._ensurePaused();
      return;
    }

    var finalIteration = this._floorWithOpenClosedRange(
        this.timing.iterationStart + this.timing._iterations(), 1.0);
    var endTimeFraction = this._modulusWithOpenClosedRange(
        this.timing.iterationStart + this.timing._iterations(), 1.0);
    if (this.currentIteration === finalIteration &&
        this._timeFraction === endTimeFraction &&
        this._intrinsicDuration() >= this.duration) {
      // We have reached the end of our final iteration, but the media element
      // is not done.
      this._ensureIsAtUnscaledTime(this.duration * endTimeFraction);
      this._ensurePaused();
      return;
    }

    // Set the appropriate playback rate.
    var playbackRate =
        this._media.defaultPlaybackRate * this._netEffectivePlaybackRate();
    if (this._media.playbackRate !== playbackRate) {
      this._media.playbackRate = playbackRate;
    }

    // Set the appropriate play/pause state. Note that we may not be able to
    // seek to the desired time. In this case, the media element's seek
    // algorithm repositions the seek to the nearest seekable time. This is OK,
    // but in this case, we don't want to play the media element, as it prevents
    // us from synchronising properly.
    if (this.player.paused ||
        !this._isSeekableUnscaledTime(this._iterationTime)) {
      this._ensurePaused();
    } else {
      this._ensurePlaying();
    }

    // Seek if required. This could be due to our AnimationPlayer being seeked,
    // or video slippage. We need to handle the fact that the video may not play
    // at exactly the right speed. There's also a variable delay when the video
    // is first played.
    // TODO: What's the right value for this delta?
    var delta = isDefinedAndNotNull(this._delta) ? this._delta :
        0.2 * Math.abs(this._media.playbackRate);
    if (Math.abs(this._iterationTime - this._unscaledMediaCurrentTime()) >
        delta) {
      this._ensureIsAtUnscaledTime(this._iterationTime);
    }
  },
  _isTargetingElement: function(element) {
    return this._media === element;
  },
  _getAnimationsTargetingElement: function() { },
  _attach: function(player) {
    this._ensurePaused();
    TimedItem.prototype._attach.call(this, player);
  }
});



/** @constructor */
var AnimationEffect = function(token) {
  if (token !== constructorToken) {
    throw new TypeError('Illegal constructor');
  }
};

AnimationEffect.prototype = {
  _sample: abstractMethod,
  clone: abstractMethod,
  toString: abstractMethod
};

var clamp = function(x, min, max) {
  return Math.max(Math.min(x, max), min);
};



/** @constructor */
var MotionPathEffect = function(path, autoRotate, angle, composite) {
  var iterationComposite = undefined;
  var spacing = undefined;
  var keyTimes = undefined;
  var keyPoints = undefined;
  var options = autoRotate;
  if (typeof options == 'string' || options instanceof String ||
      angle || composite) {
    // FIXME: add deprecation warning - please pass an options dictionary to
    // MotionPathEffect constructor
  } else if (options) {
    autoRotate = options.autoRotate;
    angle = options.angle;
    composite = options.composite;
    iterationComposite = options.iterationComposite;
    spacing = options.spacing; /* distribute or paced */
    keyTimes = options.keyTimes;
    keyPoints = options.keyPoints;
  }

  enterModifyCurrentAnimationState();
  try {
    AnimationEffect.call(this, constructorToken);

    this.composite = composite;
    this.iterationComposite = iterationComposite;
    this.spacing = spacing;
    this.keyTimes = keyTimes;
    this.keyPoints = keyPoints;

    // TODO: path argument is not in the spec -- seems useful since
    // SVGPathSegList doesn't have a constructor.
    this.autoRotate = isDefined(autoRotate) ? autoRotate : 'none';
    this.angle = isDefined(angle) ? angle : 0;
    this._path = document.createElementNS(SVG_NS, 'path');
    if (path instanceof SVGPathSegList) {
      this.segments = path;
    } else {
      var tempPath = document.createElementNS(SVG_NS, 'path');
      tempPath.setAttribute('d', String(path));
      this.segments = tempPath.pathSegList;
    }
  } finally {
    exitModifyCurrentAnimationState(null);
  }
};

MotionPathEffect.prototype = createObject(AnimationEffect.prototype, {
  get composite() {
    return this._composite;
  },
  set composite(value) {
    enterModifyCurrentAnimationState();
    try {
      // Use the default value if an invalid string is specified.
      this._composite = value === 'add' ? 'add' : 'replace';
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get iterationComposite() {
    return this._iterationComposite;
  },
  set iterationComposite(value) {
    enterModifyCurrentAnimationState();
    try {
      // Use the default value if an invalid string is specified.
      this._iterationComposite =
          value === 'accumulate' ? 'accumulate' : 'replace';
      this._updateOffsetPerIteration();
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  _sample: function(timeFraction, currentIteration, target) {
    var lengthAtTimeFraction = this._lengthAtTimeFraction(timeFraction);
    var point = this._path.getPointAtLength(lengthAtTimeFraction);
    var x = point.x - target.offsetWidth / 2;
    var y = point.y - target.offsetHeight / 2;
    if (currentIteration !== 0 && this._offsetPerIteration) {
      x += this._offsetPerIteration.x * currentIteration;
      y += this._offsetPerIteration.y * currentIteration;
    }
    // TODO: calc(point.x - 50%) doesn't work?
    var value = [{t: 'translate', d: [{px: x}, {px: y}]}];
    var angle = this.angle;
    if (this._autoRotate === 'auto-rotate') {
      // Super hacks
      var lastPoint = this._path.getPointAtLength(lengthAtTimeFraction - 0.01);
      var dx = point.x - lastPoint.x;
      var dy = point.y - lastPoint.y;
      var rotation = Math.atan2(dy, dx);
      angle += rotation / 2 / Math.PI * 360;
    }
    value.push({t: 'rotate', d: [angle]});
    compositor.setAnimatedValue(target, 'transform',
        new AddReplaceCompositableValue(value, this.composite));
  },
  _lengthAtTimeFraction: function(timeFraction) {
    timeFraction = clamp(timeFraction, 0, 1);
    if (this.spacing !== 'distribute' || !this._keyLengths) {
      return this._totalLength * timeFraction;
    }
    if (this.keyTimes) {
      var leftIndex = this._findLeftIndex(this.keyTimes, timeFraction);
      var leftLength = this._keyLengths[leftIndex];
      if (leftIndex === this.keyTimes.length - 1) {
        return leftLength;
      }
      var ratio =
          (timeFraction - this.keyTimes[leftIndex]) /
          (this.keyTimes[leftIndex + 1] - this.keyTimes[leftIndex]);

      var segmentLength = this._keyLengths[leftIndex + 1] - leftLength;
      return leftLength + ratio * segmentLength;
    }
    var segmentCount = this._cumulativeLengths.length - 1;
    if (!segmentCount) {
      return 0;
    }
    var scaledFraction = timeFraction * segmentCount;
    var index = clamp(Math.floor(scaledFraction), 0, segmentCount);
    return this._cumulativeLengths[index] + ((scaledFraction % 1) * (
        this._cumulativeLengths[index + 1] - this._cumulativeLengths[index]));
  },
  _findLeftIndex: function(array, value) {
    var leftIndex = 0;
    var rightIndex = array.length;
    while (rightIndex - leftIndex > 1) {
      var midIndex = (leftIndex + rightIndex) >> 1;
      if (array[midIndex] <= value) {
        leftIndex = midIndex;
      } else {
        rightIndex = midIndex;
      }
    }
    return leftIndex;
  },
  _updateOffsetPerIteration: function() {
    if (this.iterationComposite === 'accumulate' &&
        this._cumulativeLengths &&
        this._cumulativeLengths.length > 0) {
      this._offsetPerIteration = this._path.getPointAtLength(
          this._cumulativeLengths[this._cumulativeLengths.length - 1]);
    } else {
      this._offsetPerIteration = null;
    }
  },
  clone: function() {
    return new MotionPathEffect(this._path.getAttribute('d'));
  },
  toString: function() {
    return '<MotionPathEffect>';
  },
  set autoRotate(autoRotate) {
    enterModifyCurrentAnimationState();
    try {
      this._autoRotate = String(autoRotate);
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get autoRotate() {
    return this._autoRotate;
  },
  set angle(angle) {
    enterModifyCurrentAnimationState();
    try {
      // TODO: This should probably be a string with a unit, but the spec
      //       says it's a double.
      this._angle = Number(angle);
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get angle() {
    return this._angle;
  },
  set segments(segments) {
    enterModifyCurrentAnimationState();
    try {
      var targetSegments = this.segments;
      targetSegments.clear();
      var cumulativeLengths = [0];
      // TODO: *moving* the path segments is not correct, but pathSegList
      //       is read only
      var items = segments.numberOfItems;
      while (targetSegments.numberOfItems < items) {
        var segment = segments.removeItem(0);
        targetSegments.appendItem(segment);
        if (segment.pathSegType !== SVGPathSeg.PATHSEG_MOVETO_REL &&
            segment.pathSegType !== SVGPathSeg.PATHSEG_MOVETO_ABS) {
          cumulativeLengths.push(this._path.getTotalLength());
        }
      }
      this._cumulativeLengths = cumulativeLengths;
      this._totalLength = this._path.getTotalLength();
      var keyLengths;
      if (this.keyPoints) {
        keyLengths = [];
        for (var index = 0; index < this.keyPoints.length; ++index) {
          keyLengths.push(this.keyPoints[index] * this._totalLength);
        }
      } else {
        keyLengths = this._cumulativeLengths;
      }
      if (this.keyTimes && keyLengths.length !== this.keyTimes.length) {
        keyLengths = undefined;
      }
      this._keyLengths = keyLengths;
      this._updateOffsetPerIteration();
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  get segments() {
    return this._path.pathSegList;
  }
});

var shorthandToLonghand = {
  background: [
    'backgroundImage',
    'backgroundPosition',
    'backgroundSize',
    'backgroundRepeat',
    'backgroundAttachment',
    'backgroundOrigin',
    'backgroundClip',
    'backgroundColor'
  ],
  border: [
    'borderTopColor',
    'borderTopStyle',
    'borderTopWidth',
    'borderRightColor',
    'borderRightStyle',
    'borderRightWidth',
    'borderBottomColor',
    'borderBottomStyle',
    'borderBottomWidth',
    'borderLeftColor',
    'borderLeftStyle',
    'borderLeftWidth'
  ],
  borderBottom: [
    'borderBottomWidth',
    'borderBottomStyle',
    'borderBottomColor'
  ],
  borderColor: [
    'borderTopColor',
    'borderRightColor',
    'borderBottomColor',
    'borderLeftColor'
  ],
  borderLeft: [
    'borderLeftWidth',
    'borderLeftStyle',
    'borderLeftColor'
  ],
  borderRadius: [
    'borderTopLeftRadius',
    'borderTopRightRadius',
    'borderBottomRightRadius',
    'borderBottomLeftRadius'
  ],
  borderRight: [
    'borderRightWidth',
    'borderRightStyle',
    'borderRightColor'
  ],
  borderTop: [
    'borderTopWidth',
    'borderTopStyle',
    'borderTopColor'
  ],
  borderWidth: [
    'borderTopWidth',
    'borderRightWidth',
    'borderBottomWidth',
    'borderLeftWidth'
  ],
  font: [
    'fontFamily',
    'fontSize',
    'fontStyle',
    'fontVariant',
    'fontWeight',
    'lineHeight'
  ],
  margin: [
    'marginTop',
    'marginRight',
    'marginBottom',
    'marginLeft'
  ],
  outline: [
    'outlineColor',
    'outlineStyle',
    'outlineWidth'
  ],
  padding: [
    'paddingTop',
    'paddingRight',
    'paddingBottom',
    'paddingLeft'
  ]
};

// This delegates parsing shorthand value syntax to the browser.
var shorthandExpanderElem = createDummyElement();
var expandShorthand = function(property, value, result) {
  shorthandExpanderElem.style[property] = value;
  var longProperties = shorthandToLonghand[property];
  for (var i in longProperties) {
    var longProperty = longProperties[i];
    var longhandValue = shorthandExpanderElem.style[longProperty];
    result[longProperty] = longhandValue;
  }
};

var normalizeKeyframeDictionary = function(properties) {
  var result = {
    offset: null,
    composite: null,
    easing: presetTimingFunctions.linear
  };
  var animationProperties = [];
  for (var property in properties) {
    // TODO: Apply the CSS property to IDL attribute algorithm.
    if (property === 'offset') {
      if (typeof properties.offset === 'number') {
        result.offset = properties.offset;
      }
    } else if (property === 'composite') {
      if (properties.composite === 'add' ||
          properties.composite === 'replace') {
        result.composite = properties.composite;
      }
    } else if (property === 'easing') {
      result.easing = TimingFunction.createFromString(properties.easing);
    } else {
      // TODO: Check whether this is a supported property.
      animationProperties.push(property);
    }
  }
  // TODO: Remove prefixed properties if the unprefixed version is also
  // supported and present.
  animationProperties = animationProperties.sort(playerSortFunction);
  for (var i = 0; i < animationProperties.length; i++) {
    // TODO: Apply the IDL attribute to CSS property algorithm.
    var property = animationProperties[i];
    // TODO: The spec does not specify how to handle null values.
    // See https://www.w3.org/Bugs/Public/show_bug.cgi?id=22572
    var value = isDefinedAndNotNull(properties[property]) ?
        properties[property].toString() : '';
    if (property in shorthandToLonghand) {
      expandShorthand(property, value, result);
    } else {
      result[property] = value;
    }
  }
  return result;
};



/** @constructor */
var KeyframeEffect = function(oneOrMoreKeyframeDictionaries,
    composite) {
  enterModifyCurrentAnimationState();
  try {
    AnimationEffect.call(this, constructorToken);

    this.composite = composite;

    this.setFrames(oneOrMoreKeyframeDictionaries);
  } finally {
    exitModifyCurrentAnimationState(null);
  }
};

KeyframeEffect.prototype = createObject(AnimationEffect.prototype, {
  get composite() {
    return this._composite;
  },
  set composite(value) {
    enterModifyCurrentAnimationState();
    try {
      // Use the default value if an invalid string is specified.
      this._composite = value === 'add' ? 'add' : 'replace';
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  getFrames: function() {
    return this._keyframeDictionaries.slice(0);
  },
  setFrames: function(oneOrMoreKeyframeDictionaries) {
    enterModifyCurrentAnimationState();
    try {
      if (!Array.isArray(oneOrMoreKeyframeDictionaries)) {
        oneOrMoreKeyframeDictionaries = [oneOrMoreKeyframeDictionaries];
      }
      this._keyframeDictionaries =
          oneOrMoreKeyframeDictionaries.map(normalizeKeyframeDictionary);
      // Set lazily
      this._cachedPropertySpecificKeyframes = null;
    } finally {
      exitModifyCurrentAnimationState(repeatLastTick);
    }
  },
  _sample: function(timeFraction, currentIteration, target) {
    var frames = this._propertySpecificKeyframes();
    for (var property in frames) {
      compositor.setAnimatedValue(target, property,
          this._sampleForProperty(
              frames[property], timeFraction, currentIteration));
    }
  },
  _sampleForProperty: function(frames, timeFraction, currentIteration) {
    ASSERT_ENABLED && assert(
        frames.length >= 2,
        'Interpolation requires at least two keyframes');

    var startKeyframeIndex;
    var length = frames.length;
    // We extrapolate differently depending on whether or not there are multiple
    // keyframes at offsets of 0 and 1.
    if (timeFraction < 0.0) {
      if (frames[1].offset === 0.0) {
        return new AddReplaceCompositableValue(frames[0].rawValue(),
            this._compositeForKeyframe(frames[0]));
      } else {
        startKeyframeIndex = 0;
      }
    } else if (timeFraction >= 1.0) {
      if (frames[length - 2].offset === 1.0) {
        return new AddReplaceCompositableValue(frames[length - 1].rawValue(),
            this._compositeForKeyframe(frames[length - 1]));
      } else {
        startKeyframeIndex = length - 2;
      }
    } else {
      for (var i = length - 1; i >= 0; i--) {
        if (frames[i].offset <= timeFraction) {
          ASSERT_ENABLED && assert(frames[i].offset !== 1.0);
          startKeyframeIndex = i;
          break;
        }
      }
    }
    var startKeyframe = frames[startKeyframeIndex];
    var endKeyframe = frames[startKeyframeIndex + 1];
    if (startKeyframe.offset === timeFraction) {
      return new AddReplaceCompositableValue(startKeyframe.rawValue(),
          this._compositeForKeyframe(startKeyframe));
    }
    if (endKeyframe.offset === timeFraction) {
      return new AddReplaceCompositableValue(endKeyframe.rawValue(),
          this._compositeForKeyframe(endKeyframe));
    }
    var intervalDistance = (timeFraction - startKeyframe.offset) /
        (endKeyframe.offset - startKeyframe.offset);
    if (startKeyframe.easing) {
      intervalDistance = startKeyframe.easing.scaleTime(intervalDistance);
    }
    return new BlendedCompositableValue(
        new AddReplaceCompositableValue(startKeyframe.rawValue(),
            this._compositeForKeyframe(startKeyframe)),
        new AddReplaceCompositableValue(endKeyframe.rawValue(),
            this._compositeForKeyframe(endKeyframe)),
        intervalDistance);
  },
  _propertySpecificKeyframes: function() {
    if (isDefinedAndNotNull(this._cachedPropertySpecificKeyframes)) {
      return this._cachedPropertySpecificKeyframes;
    }

    this._cachedPropertySpecificKeyframes = {};
    var distributedFrames = this._getDistributedKeyframes();
    for (var i = 0; i < distributedFrames.length; i++) {
      for (var property in distributedFrames[i].cssValues) {
        if (!(property in this._cachedPropertySpecificKeyframes)) {
          this._cachedPropertySpecificKeyframes[property] = [];
        }
        var frame = distributedFrames[i];
        this._cachedPropertySpecificKeyframes[property].push(
            new PropertySpecificKeyframe(frame.offset, frame.composite,
                frame.easing, property, frame.cssValues[property]));
      }
    }

    for (var property in this._cachedPropertySpecificKeyframes) {
      var frames = this._cachedPropertySpecificKeyframes[property];
      ASSERT_ENABLED && assert(
          frames.length > 0,
          'There should always be keyframes for each property');

      // Add synthetic keyframes at offsets of 0 and 1 if required.
      if (frames[0].offset !== 0.0) {
        var keyframe = new PropertySpecificKeyframe(0.0, 'add',
            presetTimingFunctions.linear, property, cssNeutralValue);
        frames.unshift(keyframe);
      }
      if (frames[frames.length - 1].offset !== 1.0) {
        var keyframe = new PropertySpecificKeyframe(1.0, 'add',
            presetTimingFunctions.linear, property, cssNeutralValue);
        frames.push(keyframe);
      }
      ASSERT_ENABLED && assert(
          frames.length >= 2,
          'There should be at least two keyframes including' +
          ' synthetic keyframes');
    }

    return this._cachedPropertySpecificKeyframes;
  },
  clone: function() {
    var result = new KeyframeEffect([], this.composite);
    result._keyframeDictionaries = this._keyframeDictionaries.slice(0);
    return result;
  },
  toString: function() {
    return '<KeyframeEffect>';
  },
  _compositeForKeyframe: function(keyframe) {
    return isDefinedAndNotNull(keyframe.composite) ?
        keyframe.composite : this.composite;
  },
  _allKeyframesUseSameCompositeOperation: function(keyframes) {
    ASSERT_ENABLED && assert(
        keyframes.length >= 1, 'This requires at least one keyframe');
    var composite = this._compositeForKeyframe(keyframes[0]);
    for (var i = 1; i < keyframes.length; i++) {
      if (this._compositeForKeyframe(keyframes[i]) !== composite) {
        return false;
      }
    }
    return true;
  },
  _areKeyframeDictionariesLooselySorted: function() {
    var previousOffset = -Infinity;
    for (var i = 0; i < this._keyframeDictionaries.length; i++) {
      if (isDefinedAndNotNull(this._keyframeDictionaries[i].offset)) {
        if (this._keyframeDictionaries[i].offset < previousOffset) {
          return false;
        }
        previousOffset = this._keyframeDictionaries[i].offset;
      }
    }
    return true;
  },
  // The spec describes both this process and the process for interpretting the
  // properties of a keyframe dictionary as 'normalizing'. Here we use the term
  // 'distributing' to avoid confusion with normalizeKeyframeDictionary().
  _getDistributedKeyframes: function() {
    if (!this._areKeyframeDictionariesLooselySorted()) {
      return [];
    }

    var distributedKeyframes = this._keyframeDictionaries.map(
        KeyframeInternal.createFromNormalizedProperties);

    // Remove keyframes with offsets out of bounds.
    var length = distributedKeyframes.length;
    var count = 0;
    for (var i = 0; i < length; i++) {
      var offset = distributedKeyframes[i].offset;
      if (isDefinedAndNotNull(offset)) {
        if (offset >= 0) {
          break;
        } else {
          count = i;
        }
      }
    }
    distributedKeyframes.splice(0, count);

    length = distributedKeyframes.length;
    count = 0;
    for (var i = length - 1; i >= 0; i--) {
      var offset = distributedKeyframes[i].offset;
      if (isDefinedAndNotNull(offset)) {
        if (offset <= 1) {
          break;
        } else {
          count = length - i;
        }
      }
    }
    distributedKeyframes.splice(length - count, count);

    // Distribute offsets.
    length = distributedKeyframes.length;
    if (length > 1 && !isDefinedAndNotNull(distributedKeyframes[0].offset)) {
      distributedKeyframes[0].offset = 0;
    }
    if (length > 0 &&
        !isDefinedAndNotNull(distributedKeyframes[length - 1].offset)) {
      distributedKeyframes[length - 1].offset = 1;
    }
    var lastOffsetIndex = 0;
    var nextOffsetIndex = 0;
    for (var i = 1; i < distributedKeyframes.length - 1; i++) {
      var keyframe = distributedKeyframes[i];
      if (isDefinedAndNotNull(keyframe.offset)) {
        lastOffsetIndex = i;
        continue;
      }
      if (i > nextOffsetIndex) {
        nextOffsetIndex = i;
        while (!isDefinedAndNotNull(
            distributedKeyframes[nextOffsetIndex].offset)) {
          nextOffsetIndex++;
        }
      }
      var lastOffset = distributedKeyframes[lastOffsetIndex].offset;
      var nextOffset = distributedKeyframes[nextOffsetIndex].offset;
      var unspecifiedKeyframes = nextOffsetIndex - lastOffsetIndex - 1;
      ASSERT_ENABLED && assert(unspecifiedKeyframes > 0);
      var localIndex = i - lastOffsetIndex;
      ASSERT_ENABLED && assert(localIndex > 0);
      distributedKeyframes[i].offset = lastOffset +
          (nextOffset - lastOffset) * localIndex / (unspecifiedKeyframes + 1);
    }

    // Remove invalid property values.
    for (var i = distributedKeyframes.length - 1; i >= 0; i--) {
      var keyframe = distributedKeyframes[i];
      for (var property in keyframe.cssValues) {
        if (!KeyframeInternal.isSupportedPropertyValue(
            keyframe.cssValues[property])) {
          delete(keyframe.cssValues[property]);
        }
      }
      if (Object.keys(keyframe).length === 0) {
        distributedKeyframes.splice(i, 1);
      }
    }

    return distributedKeyframes;
  }
});



/**
 * An internal representation of a keyframe. The Keyframe type from the spec is
 * just a dictionary and is not exposed.
 *
 * @constructor
 */
var KeyframeInternal = function(offset, composite, easing) {
  ASSERT_ENABLED && assert(
      typeof offset === 'number' || offset === null,
      'Invalid offset value');
  ASSERT_ENABLED && assert(
      composite === 'add' || composite === 'replace' || composite === null,
      'Invalid composite value');
  this.offset = offset;
  this.composite = composite;
  this.easing = easing;
  this.cssValues = {};
};

KeyframeInternal.prototype = {
  addPropertyValuePair: function(property, value) {
    if (property === 'svgOffset') {
      property = 'offset';
    }
    ASSERT_ENABLED && assert(!this.cssValues.hasOwnProperty(property));
    this.cssValues[property] = value;
  }
};

KeyframeInternal.isSupportedPropertyValue = function(value) {
  ASSERT_ENABLED && assert(
      typeof value === 'string' || value === cssNeutralValue);
  // TODO: Check this properly!
  return value !== '';
};

KeyframeInternal.createFromNormalizedProperties = function(properties) {
  ASSERT_ENABLED && assert(
      isDefinedAndNotNull(properties) && typeof properties === 'object',
      'Properties must be an object');
  var keyframe = new KeyframeInternal(properties.offset, properties.composite,
      properties.easing);
  for (var candidate in properties) {
    if (candidate !== 'offset' &&
        candidate !== 'composite' &&
        candidate !== 'easing') {
      keyframe.addPropertyValuePair(candidate, properties[candidate]);
    }
  }
  return keyframe;
};



/** @constructor */
var PropertySpecificKeyframe = function(offset, composite, easing, property,
    cssValue) {
  this.offset = offset;
  this.composite = composite;
  this.easing = easing;
  this.property = property;
  this.cssValue = cssValue;
  // Calculated lazily
  this.cachedRawValue = null;
};

PropertySpecificKeyframe.prototype = {
  rawValue: function() {
    if (!isDefinedAndNotNull(this.cachedRawValue)) {
      this.cachedRawValue = fromCssValue(this.property, this.cssValue);
    }
    return this.cachedRawValue;
  }
};



/** @constructor */
var TimingFunction = function() {
  throw new TypeError('Illegal constructor');
};

TimingFunction.prototype.scaleTime = abstractMethod;

TimingFunction.createFromString = function(spec, timedItem) {
  var preset = presetTimingFunctions[spec];
  if (preset) {
    return preset;
  }
  if (spec === 'paced') {
    return presetTimingFunctions.linear;
  }
  var stepMatch = /steps\(\s*(\d+)\s*,\s*(start|end|middle)\s*\)/.exec(spec);
  if (stepMatch) {
    return new StepTimingFunction(Number(stepMatch[1]), stepMatch[2]);
  }
  var bezierMatch =
      /cubic-bezier\(([^,]*),([^,]*),([^,]*),([^)]*)\)/.exec(spec);
  if (bezierMatch) {
    return new CubicBezierTimingFunction([
      Number(bezierMatch[1]),
      Number(bezierMatch[2]),
      Number(bezierMatch[3]),
      Number(bezierMatch[4])
    ]);
  }
  return presetTimingFunctions.linear;
};



/** @constructor */
var CubicBezierTimingFunction = function(spec) {
  this.params = spec;
  this.map = [];
  for (var ii = 0; ii <= 100; ii += 1) {
    var i = ii / 100;
    this.map.push([
      3 * i * (1 - i) * (1 - i) * this.params[0] +
          3 * i * i * (1 - i) * this.params[2] + i * i * i,
      3 * i * (1 - i) * (1 - i) * this.params[1] +
          3 * i * i * (1 - i) * this.params[3] + i * i * i
    ]);
  }
};

CubicBezierTimingFunction.prototype = createObject(TimingFunction.prototype, {
  scaleTime: function(fraction) {
    var fst = 0;
    while (fst !== 100 && fraction > this.map[fst][0]) {
      fst += 1;
    }
    if (fraction === this.map[fst][0] || fst === 0) {
      return this.map[fst][1];
    }
    var yDiff = this.map[fst][1] - this.map[fst - 1][1];
    var xDiff = this.map[fst][0] - this.map[fst - 1][0];
    var p = (fraction - this.map[fst - 1][0]) / xDiff;
    return this.map[fst - 1][1] + p * yDiff;
  }
});



/** @constructor */
var StepTimingFunction = function(numSteps, position) {
  this.numSteps = numSteps;
  this.position = position || 'end';
};

StepTimingFunction.prototype = createObject(TimingFunction.prototype, {
  scaleTime: function(fraction) {
    if (fraction >= 1) {
      return 1;
    }
    var stepSize = 1 / this.numSteps;
    if (this.position === 'start') {
      fraction += stepSize;
    } else if (this.position === 'middle') {
      fraction += stepSize / 2;
    }
    return fraction - fraction % stepSize;
  }
});

var presetTimingFunctions = {
  'linear': null,
  'ease': new CubicBezierTimingFunction([0.25, 0.1, 0.25, 1.0]),
  'ease-in': new CubicBezierTimingFunction([0.42, 0, 1.0, 1.0]),
  'ease-out': new CubicBezierTimingFunction([0, 0, 0.58, 1.0]),
  'ease-in-out': new CubicBezierTimingFunction([0.42, 0, 0.58, 1.0]),
  'step-start': new StepTimingFunction(1, 'start'),
  'step-middle': new StepTimingFunction(1, 'middle'),
  'step-end': new StepTimingFunction(1, 'end')
};

var interp = function(from, to, f, type) {
  if (Array.isArray(from) || Array.isArray(to)) {
    return interpArray(from, to, f, type);
  }
  var zero = (type && type.indexOf('scale') === 0) ? 1 : 0;
  to = isDefinedAndNotNull(to) ? to : zero;
  from = isDefinedAndNotNull(from) ? from : zero;

  return to * f + from * (1 - f);
};

var interpArray = function(from, to, f, type) {
  ASSERT_ENABLED && assert(
      Array.isArray(from) || from === null,
      'From is not an array or null');
  ASSERT_ENABLED && assert(
      Array.isArray(to) || to === null,
      'To is not an array or null');
  ASSERT_ENABLED && assert(
      from === null || to === null || from.length === to.length,
      'Arrays differ in length ' + from + ' : ' + to);
  var length = from ? from.length : to.length;

  var result = [];
  for (var i = 0; i < length; i++) {
    result[i] = interp(from ? from[i] : null, to ? to[i] : null, f, type);
  }
  return result;
};

var typeWithKeywords = function(keywords, type) {
  var isKeyword;
  if (keywords.length === 1) {
    var keyword = keywords[0];
    isKeyword = function(value) {
      return value === keyword;
    };
  } else {
    isKeyword = function(value) {
      return keywords.indexOf(value) >= 0;
    };
  }
  return createObject(type, {
    add: function(base, delta) {
      if (isKeyword(base) || isKeyword(delta)) {
        return delta;
      }
      return type.add(base, delta);
    },
    interpolate: function(from, to, f) {
      if (isKeyword(from) || isKeyword(to)) {
        return nonNumericType.interpolate(from, to, f);
      }
      return type.interpolate(from, to, f);
    },
    toCssValue: function(value, svgMode) {
      return isKeyword(value) ? value : type.toCssValue(value, svgMode);
    },
    fromCssValue: function(value) {
      return isKeyword(value) ? value : type.fromCssValue(value);
    }
  });
};

var numberType = {
  add: function(base, delta) {
    // If base or delta are 'auto', we fall back to replacement.
    if (base === 'auto' || delta === 'auto') {
      return nonNumericType.add(base, delta);
    }
    return base + delta;
  },
  interpolate: function(from, to, f) {
    // If from or to are 'auto', we fall back to step interpolation.
    if (from === 'auto' || to === 'auto') {
      return nonNumericType.interpolate(from, to);
    }
    return interp(from, to, f);
  },
  toCssValue: function(value) { return value + ''; },
  fromCssValue: function(value) {
    if (value === 'auto') {
      return 'auto';
    }
    var result = Number(value);
    return isNaN(result) ? undefined : result;
  }
};

var integerType = createObject(numberType, {
  interpolate: function(from, to, f) {
    // If from or to are 'auto', we fall back to step interpolation.
    if (from === 'auto' || to === 'auto') {
      return nonNumericType.interpolate(from, to);
    }
    return Math.floor(interp(from, to, f));
  }
});

var fontWeightType = {
  add: function(base, delta) { return base + delta; },
  interpolate: function(from, to, f) {
    return interp(from, to, f);
  },
  toCssValue: function(value) {
    value = Math.round(value / 100) * 100;
    value = clamp(value, 100, 900);
    if (value === 400) {
      return 'normal';
    }
    if (value === 700) {
      return 'bold';
    }
    return String(value);
  },
  fromCssValue: function(value) {
    // TODO: support lighter / darker ?
    var out = Number(value);
    if (isNaN(out) || out < 100 || out > 900 || out % 100 !== 0) {
      return undefined;
    }
    return out;
  }
};

// This regular expression is intentionally permissive, so that
// platform-prefixed versions of calc will still be accepted as
// input. While we are restrictive with the transform property
// name, we need to be able to read underlying calc values from
// computedStyle so can't easily restrict the input here.
var outerCalcRE = /^\s*(-webkit-)?calc\s*\(\s*([^)]*)\)/;
var valueRE = /^\s*(-?[0-9]+(\.[0-9])?[0-9]*)([a-zA-Z%]*)/;
var operatorRE = /^\s*([+-])/;
var autoRE = /^\s*auto/i;
var percentLengthType = {
  zero: function() { return {}; },
  add: function(base, delta) {
    var out = {};
    for (var value in base) {
      out[value] = base[value] + (delta[value] || 0);
    }
    for (value in delta) {
      if (value in base) {
        continue;
      }
      out[value] = delta[value];
    }
    return out;
  },
  interpolate: function(from, to, f) {
    var out = {};
    for (var value in from) {
      out[value] = interp(from[value], to[value], f);
    }
    for (var value in to) {
      if (value in out) {
        continue;
      }
      out[value] = interp(0, to[value], f);
    }
    return out;
  },
  toCssValue: function(value) {
    var s = '';
    var singleValue = true;
    for (var item in value) {
      if (s === '') {
        s = value[item] + item;
      } else if (singleValue) {
        if (value[item] !== 0) {
          s = features.calcFunction +
              '(' + s + ' + ' + value[item] + item + ')';
          singleValue = false;
        }
      } else if (value[item] !== 0) {
        s = s.substring(0, s.length - 1) + ' + ' + value[item] + item + ')';
      }
    }
    return s;
  },
  fromCssValue: function(value) {
    var result = percentLengthType.consumeValueFromString(value);
    if (result) {
      return result.value;
    }
    return undefined;
  },
  consumeValueFromString: function(value) {
    if (!isDefinedAndNotNull(value)) {
      return undefined;
    }
    var autoMatch = autoRE.exec(value);
    if (autoMatch) {
      return {
        value: { auto: true },
        remaining: value.substring(autoMatch[0].length)
      };
    }
    var out = {};
    var calcMatch = outerCalcRE.exec(value);
    if (!calcMatch) {
      var singleValue = valueRE.exec(value);
      if (singleValue && (singleValue.length === 4)) {
        out[singleValue[3]] = Number(singleValue[1]);
        return {
          value: out,
          remaining: value.substring(singleValue[0].length)
        };
      }
      return undefined;
    }
    var remaining = value.substring(calcMatch[0].length);
    var calcInnards = calcMatch[2];
    var firstTime = true;
    while (true) {
      var reversed = false;
      if (firstTime) {
        firstTime = false;
      } else {
        var op = operatorRE.exec(calcInnards);
        if (!op) {
          return undefined;
        }
        if (op[1] === '-') {
          reversed = true;
        }
        calcInnards = calcInnards.substring(op[0].length);
      }
      value = valueRE.exec(calcInnards);
      if (!value) {
        return undefined;
      }
      var valueUnit = value[3];
      var valueNumber = Number(value[1]);
      if (!isDefinedAndNotNull(out[valueUnit])) {
        out[valueUnit] = 0;
      }
      if (reversed) {
        out[valueUnit] -= valueNumber;
      } else {
        out[valueUnit] += valueNumber;
      }
      calcInnards = calcInnards.substring(value[0].length);
      if (/\s*/.exec(calcInnards)[0].length === calcInnards.length) {
        return {
          value: out,
          remaining: remaining
        };
      }
    }
  },
  negate: function(value) {
    var out = {};
    for (var unit in value) {
      out[unit] = -value[unit];
    }
    return out;
  }
};

var percentLengthAutoType = typeWithKeywords(['auto'], percentLengthType);

var positionKeywordRE = /^\s*left|^\s*center|^\s*right|^\s*top|^\s*bottom/i;
var positionType = {
  zero: function() { return [{ px: 0 }, { px: 0 }]; },
  add: function(base, delta) {
    return [
      percentLengthType.add(base[0], delta[0]),
      percentLengthType.add(base[1], delta[1])
    ];
  },
  interpolate: function(from, to, f) {
    return [
      percentLengthType.interpolate(from[0], to[0], f),
      percentLengthType.interpolate(from[1], to[1], f)
    ];
  },
  toCssValue: function(value) {
    return value.map(percentLengthType.toCssValue).join(' ');
  },
  fromCssValue: function(value) {
    var tokens = positionType.consumeAllTokensFromString(value);
    if (!tokens || tokens.length > 4) {
      return undefined;
    }

    if (tokens.length === 1) {
      var token = tokens[0];
      return (positionType.isHorizontalToken(token) ?
          [token, 'center'] : ['center', token]).map(positionType.resolveToken);
    }

    if (tokens.length === 2 &&
        positionType.isHorizontalToken(tokens[0]) &&
        positionType.isVerticalToken(tokens[1])) {
      return tokens.map(positionType.resolveToken);
    }

    if (tokens.filter(positionType.isKeyword).length !== 2) {
      return undefined;
    }

    var out = [undefined, undefined];
    var center = false;
    for (var i = 0; i < tokens.length; i++) {
      var token = tokens[i];
      if (!positionType.isKeyword(token)) {
        return undefined;
      }
      if (token === 'center') {
        if (center) {
          return undefined;
        }
        center = true;
        continue;
      }
      var axis = Number(positionType.isVerticalToken(token));
      if (out[axis]) {
        return undefined;
      }
      if (i === tokens.length - 1 || positionType.isKeyword(tokens[i + 1])) {
        out[axis] = positionType.resolveToken(token);
        continue;
      }
      var percentLength = tokens[++i];
      if (token === 'bottom' || token === 'right') {
        percentLength = percentLengthType.negate(percentLength);
        percentLength['%'] = (percentLength['%'] || 0) + 100;
      }
      out[axis] = percentLength;
    }
    if (center) {
      if (!out[0]) {
        out[0] = positionType.resolveToken('center');
      } else if (!out[1]) {
        out[1] = positionType.resolveToken('center');
      } else {
        return undefined;
      }
    }
    return out.every(isDefinedAndNotNull) ? out : undefined;
  },
  consumeAllTokensFromString: function(remaining) {
    var tokens = [];
    while (remaining.trim()) {
      var result = positionType.consumeTokenFromString(remaining);
      if (!result) {
        return undefined;
      }
      tokens.push(result.value);
      remaining = result.remaining;
    }
    return tokens;
  },
  consumeTokenFromString: function(value) {
    var keywordMatch = positionKeywordRE.exec(value);
    if (keywordMatch) {
      return {
        value: keywordMatch[0].trim().toLowerCase(),
        remaining: value.substring(keywordMatch[0].length)
      };
    }
    return percentLengthType.consumeValueFromString(value);
  },
  resolveToken: function(token) {
    if (typeof token === 'string') {
      return percentLengthType.fromCssValue({
        left: '0%',
        center: '50%',
        right: '100%',
        top: '0%',
        bottom: '100%'
      }[token]);
    }
    return token;
  },
  isHorizontalToken: function(token) {
    if (typeof token === 'string') {
      return token in { left: true, center: true, right: true };
    }
    return true;
  },
  isVerticalToken: function(token) {
    if (typeof token === 'string') {
      return token in { top: true, center: true, bottom: true };
    }
    return true;
  },
  isKeyword: function(token) {
    return typeof token === 'string';
  }
};

// Spec: http://dev.w3.org/csswg/css-backgrounds/#background-position
var positionListType = {
  zero: function() { return [positionType.zero()]; },
  add: function(base, delta) {
    var out = [];
    var maxLength = Math.max(base.length, delta.length);
    for (var i = 0; i < maxLength; i++) {
      var basePosition = base[i] ? base[i] : positionType.zero();
      var deltaPosition = delta[i] ? delta[i] : positionType.zero();
      out.push(positionType.add(basePosition, deltaPosition));
    }
    return out;
  },
  interpolate: function(from, to, f) {
    var out = [];
    var maxLength = Math.max(from.length, to.length);
    for (var i = 0; i < maxLength; i++) {
      var fromPosition = from[i] ? from[i] : positionType.zero();
      var toPosition = to[i] ? to[i] : positionType.zero();
      out.push(positionType.interpolate(fromPosition, toPosition, f));
    }
    return out;
  },
  toCssValue: function(value) {
    return value.map(positionType.toCssValue).join(', ');
  },
  fromCssValue: function(value) {
    if (!isDefinedAndNotNull(value)) {
      return undefined;
    }
    if (!value.trim()) {
      return [positionType.fromCssValue('0% 0%')];
    }
    var positionValues = value.split(',');
    var out = positionValues.map(positionType.fromCssValue);
    return out.every(isDefinedAndNotNull) ? out : undefined;
  }
};

var percentLengthListType = {
  zero: function() { return [percentLengthType.zero()]; },
  add: function(base, delta) {
    var out = [];
    var maxLength = Math.max(base.length, delta.length);
    for (var i = 0; i < maxLength; i++) {
      var basePosition = base[i] ? base[i] : percentLengthType.zero();
      var deltaPosition = delta[i] ? delta[i] : percentLengthType.zero();
      out.push(percentLengthType.add(basePosition, deltaPosition));
    }
    return out;
  },
  interpolate: function(from, to, f) {
    var out = [];
    var maxLength = Math.max(from.length, to.length);
    for (var i = 0; i < maxLength; i++) {
      var fromValue = from[i] ? from[i] : percentLengthType.zero();
      var toValue = to[i] ? to[i] : percentLengthType.zero();
      out.push(percentLengthType.interpolate(fromValue, toValue, f));
    }
    return out;
  },
  toCssValue: function(value) {
    return value.map(percentLengthType.toCssValue).join(', ');
  },
  fromCssValue: function(value) {
    if (!isDefinedAndNotNull(value)) {
      return undefined;
    }
    if (!value.trim()) {
      return [percentLengthType.fromCssValue('0%')];
    }
    var values = value.split(/\s*,\s*|\s+/);
    var out = values.map(percentLengthType.fromCssValue);
    return out.every(isDefinedAndNotNull) ? out : undefined;
  }
};

var numberListType = {
  zero: function() { return [0]; },
  add: function(base, delta) {
    var out = [];
    var maxLength = Math.max(base.length, delta.length);
    for (var i = 0; i < maxLength; i++) {
      var basePosition = base[i] ? base[i] : 0;
      var deltaPosition = delta[i] ? delta[i] : 0;
      out.push(numberType.add(basePosition, deltaPosition));
    }
    return out;
  },
  interpolate: function(from, to, f) {
    var out = [];
    var maxLength = Math.max(from.length, to.length);
    for (var i = 0; i < maxLength; i++) {
      var fromValue = from[i] ? from[i] : 0;
      var toValue = to[i] ? to[i] : 0;
      out.push(numberType.interpolate(fromValue, toValue, f));
    }
    return out;
  },
  toCssValue: function(value) {
    return value.map(numberType.toCssValue).join(', ');
  },
  fromCssValue: function(value) {
    if (!isDefinedAndNotNull(value)) {
      return undefined;
    }
    if (!value.trim()) {
      return [numberType.fromCssValue('0%')];
    }
    var values = value.split(/\s*,\s*|\s+/);
    var out = values.map(numberType.fromCssValue);
    return out.every(isDefinedAndNotNull) ? out : undefined;
  }
};

var rectangleRE = /rect\(([^,]+),([^,]+),([^,]+),([^)]+)\)/;
var rectangleType = {
  add: function(base, delta) {
    return {
      top: percentLengthType.add(base.top, delta.top),
      right: percentLengthType.add(base.right, delta.right),
      bottom: percentLengthType.add(base.bottom, delta.bottom),
      left: percentLengthType.add(base.left, delta.left)
    };
  },
  interpolate: function(from, to, f) {
    return {
      top: percentLengthType.interpolate(from.top, to.top, f),
      right: percentLengthType.interpolate(from.right, to.right, f),
      bottom: percentLengthType.interpolate(from.bottom, to.bottom, f),
      left: percentLengthType.interpolate(from.left, to.left, f)
    };
  },
  toCssValue: function(value) {
    return 'rect(' +
        percentLengthType.toCssValue(value.top) + ',' +
        percentLengthType.toCssValue(value.right) + ',' +
        percentLengthType.toCssValue(value.bottom) + ',' +
        percentLengthType.toCssValue(value.left) + ')';
  },
  fromCssValue: function(value) {
    var match = rectangleRE.exec(value);
    if (!match) {
      return undefined;
    }
    var out = {
      top: percentLengthType.fromCssValue(match[1]),
      right: percentLengthType.fromCssValue(match[2]),
      bottom: percentLengthType.fromCssValue(match[3]),
      left: percentLengthType.fromCssValue(match[4])
    };
    if (out.top && out.right && out.bottom && out.left) {
      return out;
    }
    return undefined;
  }
};

var originType = {
  zero: function() { return [{'%': 0}, {'%': 0}, {px: 0}]; },
  add: function(base, delta) {
    return [
      percentLengthType.add(base[0], delta[0]),
      percentLengthType.add(base[1], delta[1]),
      percentLengthType.add(base[2], delta[2])
    ];
  },
  interpolate: function(from, to, f) {
    return [
      percentLengthType.interpolate(from[0], to[0], f),
      percentLengthType.interpolate(from[1], to[1], f),
      percentLengthType.interpolate(from[2], to[2], f)
    ];
  },
  toCssValue: function(value) {
    var result = percentLengthType.toCssValue(value[0]) + ' ' +
        percentLengthType.toCssValue(value[1]);
    // Return the third value if it is non-zero.
    for (var unit in value[2]) {
      if (value[2][unit] !== 0) {
        return result + ' ' + percentLengthType.toCssValue(value[2]);
      }
    }
    return result;
  },
  fromCssValue: function(value) {
    var tokens = positionType.consumeAllTokensFromString(value);
    if (!tokens) {
      return undefined;
    }
    var out = ['center', 'center', {px: 0}];
    switch (tokens.length) {
      case 0:
        return originType.zero();
      case 1:
        if (positionType.isHorizontalToken(tokens[0])) {
          out[0] = tokens[0];
        } else if (positionType.isVerticalToken(tokens[0])) {
          out[1] = tokens[0];
        } else {
          return undefined;
        }
        return out.map(positionType.resolveToken);
      case 3:
        if (positionType.isKeyword(tokens[2])) {
          return undefined;
        }
        out[2] = tokens[2];
      case 2:
        if (positionType.isHorizontalToken(tokens[0]) &&
            positionType.isVerticalToken(tokens[1])) {
          out[0] = tokens[0];
          out[1] = tokens[1];
        } else if (positionType.isVerticalToken(tokens[0]) &&
            positionType.isHorizontalToken(tokens[1])) {
          out[0] = tokens[1];
          out[1] = tokens[0];
        } else {
          return undefined;
        }
        return out.map(positionType.resolveToken);
      default:
        return undefined;
    }
  }
};

var shadowType = {
  zero: function() {
    return {
      hOffset: lengthType.zero(),
      vOffset: lengthType.zero()
    };
  },
  _addSingle: function(base, delta) {
    if (base && delta && base.inset !== delta.inset) {
      return delta;
    }
    var result = {
      inset: base ? base.inset : delta.inset,
      hOffset: lengthType.add(
          base ? base.hOffset : lengthType.zero(),
          delta ? delta.hOffset : lengthType.zero()),
      vOffset: lengthType.add(
          base ? base.vOffset : lengthType.zero(),
          delta ? delta.vOffset : lengthType.zero()),
      blur: lengthType.add(
          base && base.blur || lengthType.zero(),
          delta && delta.blur || lengthType.zero())
    };
    if (base && base.spread || delta && delta.spread) {
      result.spread = lengthType.add(
          base && base.spread || lengthType.zero(),
          delta && delta.spread || lengthType.zero());
    }
    if (base && base.color || delta && delta.color) {
      result.color = colorType.add(
          base && base.color || colorType.zero(),
          delta && delta.color || colorType.zero());
    }
    return result;
  },
  add: function(base, delta) {
    var result = [];
    for (var i = 0; i < base.length || i < delta.length; i++) {
      result.push(this._addSingle(base[i], delta[i]));
    }
    return result;
  },
  _interpolateSingle: function(from, to, f) {
    if (from && to && from.inset !== to.inset) {
      return f < 0.5 ? from : to;
    }
    var result = {
      inset: from ? from.inset : to.inset,
      hOffset: lengthType.interpolate(
          from ? from.hOffset : lengthType.zero(),
          to ? to.hOffset : lengthType.zero(), f),
      vOffset: lengthType.interpolate(
          from ? from.vOffset : lengthType.zero(),
          to ? to.vOffset : lengthType.zero(), f),
      blur: lengthType.interpolate(
          from && from.blur || lengthType.zero(),
          to && to.blur || lengthType.zero(), f)
    };
    if (from && from.spread || to && to.spread) {
      result.spread = lengthType.interpolate(
          from && from.spread || lengthType.zero(),
          to && to.spread || lengthType.zero(), f);
    }
    if (from && from.color || to && to.color) {
      result.color = colorType.interpolate(
          from && from.color || colorType.zero(),
          to && to.color || colorType.zero(), f);
    }
    return result;
  },
  interpolate: function(from, to, f) {
    var result = [];
    for (var i = 0; i < from.length || i < to.length; i++) {
      result.push(this._interpolateSingle(from[i], to[i], f));
    }
    return result;
  },
  _toCssValueSingle: function(value) {
    return (value.inset ? 'inset ' : '') +
        lengthType.toCssValue(value.hOffset) + ' ' +
        lengthType.toCssValue(value.vOffset) + ' ' +
        lengthType.toCssValue(value.blur) +
        (value.spread ? ' ' + lengthType.toCssValue(value.spread) : '') +
        (value.color ? ' ' + colorType.toCssValue(value.color) : '');
  },
  toCssValue: function(value) {
    return value.map(this._toCssValueSingle).join(', ');
  },
  fromCssValue: function(value) {
    var shadowRE = /(([^(,]+(\([^)]*\))?)+)/g;
    var match;
    var shadows = [];
    while ((match = shadowRE.exec(value)) !== null) {
      shadows.push(match[0]);
    }

    var result = shadows.map(function(value) {
      if (value === 'none') {
        return shadowType.zero();
      }
      value = value.replace(/^\s+|\s+$/g, '');

      var partsRE = /([^ (]+(\([^)]*\))?)/g;
      var parts = [];
      while ((match = partsRE.exec(value)) !== null) {
        parts.push(match[0]);
      }

      if (parts.length < 2 || parts.length > 7) {
        return undefined;
      }
      var result = {
        inset: false
      };

      var lengths = [];
      while (parts.length) {
        var part = parts.shift();

        var length = lengthType.fromCssValue(part);
        if (length) {
          lengths.push(length);
          continue;
        }

        var color = colorType.fromCssValue(part);
        if (color) {
          result.color = color;
        }

        if (part === 'inset') {
          result.inset = true;
        }
      }

      if (lengths.length < 2 || lengths.length > 4) {
        return undefined;
      }
      result.hOffset = lengths[0];
      result.vOffset = lengths[1];
      if (lengths.length > 2) {
        result.blur = lengths[2];
      }
      if (lengths.length > 3) {
        result.spread = lengths[3];
      }
      return result;
    });

    return result.every(isDefined) ? result : undefined;
  }
};

var nonNumericType = {
  add: function(base, delta) {
    return isDefined(delta) ? delta : base;
  },
  interpolate: function(from, to, f) {
    return f < 0.5 ? from : to;
  },
  toCssValue: function(value) {
    return value;
  },
  fromCssValue: function(value) {
    return value;
  }
};

var visibilityType = createObject(nonNumericType, {
  interpolate: function(from, to, f) {
    if (from !== 'visible' && to !== 'visible') {
      return nonNumericType.interpolate(from, to, f);
    }
    if (f <= 0) {
      return from;
    }
    if (f >= 1) {
      return to;
    }
    return 'visible';
  },
  fromCssValue: function(value) {
    if (['visible', 'hidden', 'collapse'].indexOf(value) !== -1) {
      return value;
    }
    return undefined;
  }
});

var lengthType = percentLengthType;
var lengthAutoType = typeWithKeywords(['auto'], lengthType);

var colorRE = new RegExp(
    '(hsla?|rgba?)\\(' +
    '([\\-0-9]+%?),?\\s*' +
    '([\\-0-9]+%?),?\\s*' +
    '([\\-0-9]+%?)(?:,?\\s*([\\-0-9\\.]+%?))?' +
    '\\)');
var colorHashRE = new RegExp(
    '#([0-9A-Fa-f][0-9A-Fa-f]?)' +
    '([0-9A-Fa-f][0-9A-Fa-f]?)' +
    '([0-9A-Fa-f][0-9A-Fa-f]?)');

function hsl2rgb(h, s, l) {
  // Cribbed from http://dev.w3.org/csswg/css-color/#hsl-color
  // Wrap to 0->360 degrees (IE -10 === 350) then normalize
  h = (((h % 360) + 360) % 360) / 360;
  s = s / 100;
  l = l / 100;
  function hue2rgb(m1, m2, h) {
    if (h < 0) {
      h += 1;
    }
    if (h > 1) {
      h -= 1;
    }
    if (h * 6 < 1) {
      return m1 + (m2 - m1) * h * 6;
    }
    if (h * 2 < 1) {
      return m2;
    }
    if (h * 3 < 2) {
      return m1 + (m2 - m1) * (2 / 3 - h) * 6;
    }
    return m1;
  }
  var m2;
  if (l <= 0.5) {
    m2 = l * (s + 1);
  } else {
    m2 = l + s - l * s;
  }

  var m1 = l * 2 - m2;
  var r = Math.ceil(hue2rgb(m1, m2, h + 1 / 3) * 255);
  var g = Math.ceil(hue2rgb(m1, m2, h) * 255);
  var b = Math.ceil(hue2rgb(m1, m2, h - 1 / 3) * 255);
  return [r, g, b];
}

var namedColors = {
  aliceblue: [240, 248, 255, 1],
  antiquewhite: [250, 235, 215, 1],
  aqua: [0, 255, 255, 1],
  aquamarine: [127, 255, 212, 1],
  azure: [240, 255, 255, 1],
  beige: [245, 245, 220, 1],
  bisque: [255, 228, 196, 1],
  black: [0, 0, 0, 1],
  blanchedalmond: [255, 235, 205, 1],
  blue: [0, 0, 255, 1],
  blueviolet: [138, 43, 226, 1],
  brown: [165, 42, 42, 1],
  burlywood: [222, 184, 135, 1],
  cadetblue: [95, 158, 160, 1],
  chartreuse: [127, 255, 0, 1],
  chocolate: [210, 105, 30, 1],
  coral: [255, 127, 80, 1],
  cornflowerblue: [100, 149, 237, 1],
  cornsilk: [255, 248, 220, 1],
  crimson: [220, 20, 60, 1],
  cyan: [0, 255, 255, 1],
  darkblue: [0, 0, 139, 1],
  darkcyan: [0, 139, 139, 1],
  darkgoldenrod: [184, 134, 11, 1],
  darkgray: [169, 169, 169, 1],
  darkgreen: [0, 100, 0, 1],
  darkgrey: [169, 169, 169, 1],
  darkkhaki: [189, 183, 107, 1],
  darkmagenta: [139, 0, 139, 1],
  darkolivegreen: [85, 107, 47, 1],
  darkorange: [255, 140, 0, 1],
  darkorchid: [153, 50, 204, 1],
  darkred: [139, 0, 0, 1],
  darksalmon: [233, 150, 122, 1],
  darkseagreen: [143, 188, 143, 1],
  darkslateblue: [72, 61, 139, 1],
  darkslategray: [47, 79, 79, 1],
  darkslategrey: [47, 79, 79, 1],
  darkturquoise: [0, 206, 209, 1],
  darkviolet: [148, 0, 211, 1],
  deeppink: [255, 20, 147, 1],
  deepskyblue: [0, 191, 255, 1],
  dimgray: [105, 105, 105, 1],
  dimgrey: [105, 105, 105, 1],
  dodgerblue: [30, 144, 255, 1],
  firebrick: [178, 34, 34, 1],
  floralwhite: [255, 250, 240, 1],
  forestgreen: [34, 139, 34, 1],
  fuchsia: [255, 0, 255, 1],
  gainsboro: [220, 220, 220, 1],
  ghostwhite: [248, 248, 255, 1],
  gold: [255, 215, 0, 1],
  goldenrod: [218, 165, 32, 1],
  gray: [128, 128, 128, 1],
  green: [0, 128, 0, 1],
  greenyellow: [173, 255, 47, 1],
  grey: [128, 128, 128, 1],
  honeydew: [240, 255, 240, 1],
  hotpink: [255, 105, 180, 1],
  indianred: [205, 92, 92, 1],
  indigo: [75, 0, 130, 1],
  ivory: [255, 255, 240, 1],
  khaki: [240, 230, 140, 1],
  lavender: [230, 230, 250, 1],
  lavenderblush: [255, 240, 245, 1],
  lawngreen: [124, 252, 0, 1],
  lemonchiffon: [255, 250, 205, 1],
  lightblue: [173, 216, 230, 1],
  lightcoral: [240, 128, 128, 1],
  lightcyan: [224, 255, 255, 1],
  lightgoldenrodyellow: [250, 250, 210, 1],
  lightgray: [211, 211, 211, 1],
  lightgreen: [144, 238, 144, 1],
  lightgrey: [211, 211, 211, 1],
  lightpink: [255, 182, 193, 1],
  lightsalmon: [255, 160, 122, 1],
  lightseagreen: [32, 178, 170, 1],
  lightskyblue: [135, 206, 250, 1],
  lightslategray: [119, 136, 153, 1],
  lightslategrey: [119, 136, 153, 1],
  lightsteelblue: [176, 196, 222, 1],
  lightyellow: [255, 255, 224, 1],
  lime: [0, 255, 0, 1],
  limegreen: [50, 205, 50, 1],
  linen: [250, 240, 230, 1],
  magenta: [255, 0, 255, 1],
  maroon: [128, 0, 0, 1],
  mediumaquamarine: [102, 205, 170, 1],
  mediumblue: [0, 0, 205, 1],
  mediumorchid: [186, 85, 211, 1],
  mediumpurple: [147, 112, 219, 1],
  mediumseagreen: [60, 179, 113, 1],
  mediumslateblue: [123, 104, 238, 1],
  mediumspringgreen: [0, 250, 154, 1],
  mediumturquoise: [72, 209, 204, 1],
  mediumvioletred: [199, 21, 133, 1],
  midnightblue: [25, 25, 112, 1],
  mintcream: [245, 255, 250, 1],
  mistyrose: [255, 228, 225, 1],
  moccasin: [255, 228, 181, 1],
  navajowhite: [255, 222, 173, 1],
  navy: [0, 0, 128, 1],
  oldlace: [253, 245, 230, 1],
  olive: [128, 128, 0, 1],
  olivedrab: [107, 142, 35, 1],
  orange: [255, 165, 0, 1],
  orangered: [255, 69, 0, 1],
  orchid: [218, 112, 214, 1],
  palegoldenrod: [238, 232, 170, 1],
  palegreen: [152, 251, 152, 1],
  paleturquoise: [175, 238, 238, 1],
  palevioletred: [219, 112, 147, 1],
  papayawhip: [255, 239, 213, 1],
  peachpuff: [255, 218, 185, 1],
  peru: [205, 133, 63, 1],
  pink: [255, 192, 203, 1],
  plum: [221, 160, 221, 1],
  powderblue: [176, 224, 230, 1],
  purple: [128, 0, 128, 1],
  red: [255, 0, 0, 1],
  rosybrown: [188, 143, 143, 1],
  royalblue: [65, 105, 225, 1],
  saddlebrown: [139, 69, 19, 1],
  salmon: [250, 128, 114, 1],
  sandybrown: [244, 164, 96, 1],
  seagreen: [46, 139, 87, 1],
  seashell: [255, 245, 238, 1],
  sienna: [160, 82, 45, 1],
  silver: [192, 192, 192, 1],
  skyblue: [135, 206, 235, 1],
  slateblue: [106, 90, 205, 1],
  slategray: [112, 128, 144, 1],
  slategrey: [112, 128, 144, 1],
  snow: [255, 250, 250, 1],
  springgreen: [0, 255, 127, 1],
  steelblue: [70, 130, 180, 1],
  tan: [210, 180, 140, 1],
  teal: [0, 128, 128, 1],
  thistle: [216, 191, 216, 1],
  tomato: [255, 99, 71, 1],
  transparent: [0, 0, 0, 0],
  turquoise: [64, 224, 208, 1],
  violet: [238, 130, 238, 1],
  wheat: [245, 222, 179, 1],
  white: [255, 255, 255, 1],
  whitesmoke: [245, 245, 245, 1],
  yellow: [255, 255, 0, 1],
  yellowgreen: [154, 205, 50, 1]
};

// SVG fill and stroke accept none and currentColor
// http://www.w3.org/TR/SVG/painting.html#SpecifyingPaint
var colorType = typeWithKeywords(['currentColor', 'none'], {
  zero: function() { return [0, 0, 0, 0]; },
  _premultiply: function(value) {
    var alpha = value[3];
    return [value[0] * alpha, value[1] * alpha, value[2] * alpha];
  },
  add: function(base, delta) {
    var alpha = Math.min(base[3] + delta[3], 1);
    if (alpha === 0) {
      return [0, 0, 0, 0];
    }
    base = this._premultiply(base);
    delta = this._premultiply(delta);
    return [(base[0] + delta[0]) / alpha, (base[1] + delta[1]) / alpha,
            (base[2] + delta[2]) / alpha, alpha];
  },
  interpolate: function(from, to, f) {
    var alpha = clamp(interp(from[3], to[3], f), 0, 1);
    if (alpha === 0) {
      return [0, 0, 0, 0];
    }
    from = this._premultiply(from);
    to = this._premultiply(to);
    return [interp(from[0], to[0], f) / alpha,
            interp(from[1], to[1], f) / alpha,
            interp(from[2], to[2], f) / alpha, alpha];
  },
  toCssValue: function(value) {
    if (value === undefined) {
      return undefined;
    }
    return 'rgba(' + Math.round(value[0]) + ', ' + Math.round(value[1]) +
        ', ' + Math.round(value[2]) + ', ' + value[3] + ')';
  },
  fromCssValue: function(value) {
    // http://dev.w3.org/csswg/css-color/#color
    var out = [];

    var regexResult = colorHashRE.exec(value);
    if (regexResult) {
      if (value.length !== 4 && value.length !== 7) {
        return undefined;
      }

      var out = [];
      regexResult.shift();
      for (var i = 0; i < 3; i++) {
        if (regexResult[i].length === 1) {
          regexResult[i] = regexResult[i] + regexResult[i];
        }
        var v = Math.max(Math.min(parseInt(regexResult[i], 16), 255), 0);
        out[i] = v;
      }
      out.push(1.0);
    }

    var regexResult = colorRE.exec(value);
    if (regexResult) {
      regexResult.shift();
      var type = regexResult.shift().substr(0, 3);
      for (var i = 0; i < 3; i++) {
        var m = 1;
        if (regexResult[i][regexResult[i].length - 1] === '%') {
          regexResult[i] = regexResult[i].substr(0, regexResult[i].length - 1);
          m = 255.0 / 100.0;
        }
        if (type === 'rgb') {
          out[i] = clamp(Math.round(parseInt(regexResult[i], 10) * m), 0, 255);
        } else {
          out[i] = parseInt(regexResult[i], 10);
        }
      }

      // Convert hsl values to rgb value
      if (type === 'hsl') {
        out = hsl2rgb.apply(null, out);
      }

      if (typeof regexResult[3] !== 'undefined') {
        out[3] = Math.max(Math.min(parseFloat(regexResult[3]), 1.0), 0.0);
      } else {
        out.push(1.0);
      }
    }

    if (out.some(isNaN)) {
      return undefined;
    }
    if (out.length > 0) {
      return out;
    }
    return namedColors[value];
  }
});

var convertToDeg = function(num, type) {
  switch (type) {
    case 'grad':
      return num / 400 * 360;
    case 'rad':
      return num / 2 / Math.PI * 360;
    case 'turn':
      return num * 360;
    default:
      return num;
  }
};

var extractValue = function(values, pos, hasUnits) {
  var value = Number(values[pos]);
  if (!hasUnits) {
    return value;
  }
  var type = values[pos + 1];
  if (type === '') { type = 'px'; }
  var result = {};
  result[type] = value;
  return result;
};

var extractValues = function(values, numValues, numOptionalValues,
    hasUnits) {
  var result = [];
  var pos = 1; // values has the matched text as the first item

  for (var i = 0; i < numValues; i++) {
    result.push(extractValue(values, pos, hasUnits));
    pos += 2; // move past number and units
  }
  for (var i = 0; i < numOptionalValues && values[pos]; i++) {
    result.push(extractValue(values, pos, hasUnits));
    pos += 2; // move past number and units
  }
  return result;
};

var SPACES = '\\s*';
var MANDATORY_SPACES = '\\s+';
var NUMBER = '[+-]?(?:\\d+|\\d*\\.\\d+)';
var RAW_OPEN_BRACKET = '\\(';
var RAW_CLOSE_BRACKET = '\\)';
var RAW_COMMA = ',';
var UNIT = '[a-zA-Z%]*';
var START = '^';

function capture(x) { return '(' + x + ')'; }
function optional(x) { return '(?:' + x + ')?'; }

var OPEN_BRACKET = [SPACES, RAW_OPEN_BRACKET, SPACES].join('');
var CLOSE_BRACKET = [SPACES, RAW_CLOSE_BRACKET, SPACES].join('');
var COMMA = [SPACES, RAW_COMMA, SPACES].join('');
var UNIT_NUMBER = [capture(NUMBER), capture(UNIT)].join('');

function transformRE(name, numParms, numOptionalParms, commaDelimited) {
  var tokenList = [START, SPACES, name, OPEN_BRACKET];
  var separator = commaDelimited ? COMMA : MANDATORY_SPACES;
  for (var i = 0; i < numParms - 1; i++) {
    tokenList.push(UNIT_NUMBER);
    tokenList.push(separator);
  }
  tokenList.push(UNIT_NUMBER);
  for (var i = 0; i < numOptionalParms; i++) {
    tokenList.push(optional([separator, UNIT_NUMBER].join('')));
  }
  tokenList.push(CLOSE_BRACKET);
  return new RegExp(tokenList.join(''));
}

function buildMatcher(name, numValues, numOptionalValues, commaDelimited,
    hasUnits, baseValue) {
  var baseName = name;
  if (baseValue) {
    if (name[name.length - 1] === 'X' || name[name.length - 1] === 'Y') {
      baseName = name.substring(0, name.length - 1);
    } else if (name[name.length - 1] === 'Z') {
      baseName = name.substring(0, name.length - 1) + '3d';
    }
  }

  var f = function(x) {
    var r = extractValues(x, numValues, numOptionalValues, hasUnits);
    if (baseValue !== undefined) {
      if (name[name.length - 1] === 'X') {
        r.push(baseValue);
      } else if (name[name.length - 1] === 'Y') {
        r = [baseValue].concat(r);
      } else if (name[name.length - 1] === 'Z') {
        r = [baseValue, baseValue].concat(r);
      } else if (numOptionalValues >= 1) {
        while (r.length < 2) {
          if (baseValue === 'copy') {
            r.push(r[0]);
          } else {
            r.push(baseValue);
          }
        }
      }
    }
    return r;
  };
  return [transformRE(name, numValues, numOptionalValues, commaDelimited),
      f, baseName];
}

function buildSingleValueMatcher(name, hasUnits, baseValue) {
  return buildMatcher(name, 1, 0, true, hasUnits, baseValue);
}

function buildRotationMatcher(name, numValues, numOptionalValues, baseValue) {
  var m = buildMatcher(name, numValues, numOptionalValues, true,
      true, baseValue);

  var f = function(x) {
    var r = m[1](x);
    return r.map(function(v) {
      var result = 0;
      for (var type in v) {
        result += convertToDeg(v[type], type);
      }
      return result;
    });
  };
  return [m[0], f, m[2]];
}

function build3DRotationMatcher() {
  var m = buildMatcher('rotate3d', 4, 0, true, true);
  var f = function(x) {
    var r = m[1](x);
    var out = [];
    for (var i = 0; i < 3; i++) {
      out.push(r[i].px);
    }
    var angle = 0;
    for (var unit in r[3]) {
      angle += convertToDeg(r[3][unit], unit);
    }
    out.push(angle);
    return out;
  };
  return [m[0], f, m[2]];
}

var transformREs = [
  buildRotationMatcher('rotate', 1, 2),
  buildRotationMatcher('rotateX', 1, 0),
  buildRotationMatcher('rotateY', 1, 0),
  buildRotationMatcher('rotateZ', 1, 0),
  build3DRotationMatcher(),
  buildRotationMatcher('skew', 1, 1, 0),
  buildRotationMatcher('skewX', 1, 0),
  buildRotationMatcher('skewY', 1, 0),
  buildSingleValueMatcher('translateX', true, {px: 0}),
  buildSingleValueMatcher('translateY', true, {px: 0}),
  buildSingleValueMatcher('translateZ', true, {px: 0}),
  buildMatcher('translate', 1, 1, true, true, {px: 0}),
  buildMatcher('translate3d', 3, 0, true, true),
  buildMatcher('scale', 1, 1, true, false, 'copy'),
  buildSingleValueMatcher('scaleX', false, 1),
  buildSingleValueMatcher('scaleY', false, 1),
  buildSingleValueMatcher('scaleZ', false, 1),
  buildMatcher('scale3d', 3, 0, true, false),
  buildSingleValueMatcher('perspective', true),
  buildMatcher('matrix', 6, 0, true, false),
  buildMatcher('matrix3d', 16, 0, true, false)
];

var decomposeMatrix = (function() {
  // this is only ever used on the perspective matrix, which has 0, 0, 0, 1 as
  // last column
  function determinant(m) {
    return m[0][0] * m[1][1] * m[2][2] +
           m[1][0] * m[2][1] * m[0][2] +
           m[2][0] * m[0][1] * m[1][2] -
           m[0][2] * m[1][1] * m[2][0] -
           m[1][2] * m[2][1] * m[0][0] -
           m[2][2] * m[0][1] * m[1][0];
  }

  // from Wikipedia:
  //
  // [A B]^-1 = [A^-1 + A^-1B(D - CA^-1B)^-1CA^-1     -A^-1B(D - CA^-1B)^-1]
  // [C D]      [-(D - CA^-1B)^-1CA^-1                (D - CA^-1B)^-1      ]
  //
  // Therefore
  //
  // [A [0]]^-1 = [A^-1       [0]]
  // [C  1 ]      [ -CA^-1     1 ]
  function inverse(m) {
    var iDet = 1 / determinant(m);
    var a = m[0][0], b = m[0][1], c = m[0][2];
    var d = m[1][0], e = m[1][1], f = m[1][2];
    var g = m[2][0], h = m[2][1], k = m[2][2];
    var Ainv = [
      [(e * k - f * h) * iDet, (c * h - b * k) * iDet,
       (b * f - c * e) * iDet, 0],
      [(f * g - d * k) * iDet, (a * k - c * g) * iDet,
       (c * d - a * f) * iDet, 0],
      [(d * h - e * g) * iDet, (g * b - a * h) * iDet,
       (a * e - b * d) * iDet, 0]
    ];
    var lastRow = [];
    for (var i = 0; i < 3; i++) {
      var val = 0;
      for (var j = 0; j < 3; j++) {
        val += m[3][j] * Ainv[j][i];
      }
      lastRow.push(val);
    }
    lastRow.push(1);
    Ainv.push(lastRow);
    return Ainv;
  }

  function transposeMatrix4(m) {
    return [[m[0][0], m[1][0], m[2][0], m[3][0]],
            [m[0][1], m[1][1], m[2][1], m[3][1]],
            [m[0][2], m[1][2], m[2][2], m[3][2]],
            [m[0][3], m[1][3], m[2][3], m[3][3]]];
  }

  function multVecMatrix(v, m) {
    var result = [];
    for (var i = 0; i < 4; i++) {
      var val = 0;
      for (var j = 0; j < 4; j++) {
        val += v[j] * m[j][i];
      }
      result.push(val);
    }
    return result;
  }

  function normalize(v) {
    var len = length(v);
    return [v[0] / len, v[1] / len, v[2] / len];
  }

  function length(v) {
    return Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
  }

  function combine(v1, v2, v1s, v2s) {
    return [v1s * v1[0] + v2s * v2[0], v1s * v1[1] + v2s * v2[1],
            v1s * v1[2] + v2s * v2[2]];
  }

  function cross(v1, v2) {
    return [v1[1] * v2[2] - v1[2] * v2[1],
            v1[2] * v2[0] - v1[0] * v2[2],
            v1[0] * v2[1] - v1[1] * v2[0]];
  }

  // TODO: Implement 2D matrix decomposition.
  // http://dev.w3.org/csswg/css-transforms/#decomposing-a-2d-matrix
  function decomposeMatrix(matrix) {
    var m3d = [
      matrix.slice(0, 4),
      matrix.slice(4, 8),
      matrix.slice(8, 12),
      matrix.slice(12, 16)
    ];

    // skip normalization step as m3d[3][3] should always be 1
    if (m3d[3][3] !== 1) {
      throw 'attempt to decompose non-normalized matrix';
    }

    var perspectiveMatrix = m3d.concat(); // copy m3d
    for (var i = 0; i < 3; i++) {
      perspectiveMatrix[i][3] = 0;
    }

    if (determinant(perspectiveMatrix) === 0) {
      return false;
    }

    var rhs = [];

    var perspective;
    if (m3d[0][3] !== 0 || m3d[1][3] !== 0 || m3d[2][3] !== 0) {
      rhs.push(m3d[0][3]);
      rhs.push(m3d[1][3]);
      rhs.push(m3d[2][3]);
      rhs.push(m3d[3][3]);

      var inversePerspectiveMatrix = inverse(perspectiveMatrix);
      var transposedInversePerspectiveMatrix =
          transposeMatrix4(inversePerspectiveMatrix);
      perspective = multVecMatrix(rhs, transposedInversePerspectiveMatrix);
    } else {
      perspective = [0, 0, 0, 1];
    }

    var translate = m3d[3].slice(0, 3);

    var row = [];
    row.push(m3d[0].slice(0, 3));
    var scale = [];
    scale.push(length(row[0]));
    row[0] = normalize(row[0]);

    var skew = [];
    row.push(m3d[1].slice(0, 3));
    skew.push(dot(row[0], row[1]));
    row[1] = combine(row[1], row[0], 1.0, -skew[0]);

    scale.push(length(row[1]));
    row[1] = normalize(row[1]);
    skew[0] /= scale[1];

    row.push(m3d[2].slice(0, 3));
    skew.push(dot(row[0], row[2]));
    row[2] = combine(row[2], row[0], 1.0, -skew[1]);
    skew.push(dot(row[1], row[2]));
    row[2] = combine(row[2], row[1], 1.0, -skew[2]);

    scale.push(length(row[2]));
    row[2] = normalize(row[2]);
    skew[1] /= scale[2];
    skew[2] /= scale[2];

    var pdum3 = cross(row[1], row[2]);
    if (dot(row[0], pdum3) < 0) {
      for (var i = 0; i < 3; i++) {
        scale[i] *= -1;
        row[i][0] *= -1;
        row[i][1] *= -1;
        row[i][2] *= -1;
      }
    }

    var t = row[0][0] + row[1][1] + row[2][2] + 1;
    var s;
    var quaternion;

    if (t > 1e-4) {
      s = 0.5 / Math.sqrt(t);
      quaternion = [
        (row[2][1] - row[1][2]) * s,
        (row[0][2] - row[2][0]) * s,
        (row[1][0] - row[0][1]) * s,
        0.25 / s
      ];
    } else if (row[0][0] > row[1][1] && row[0][0] > row[2][2]) {
      s = Math.sqrt(1 + row[0][0] - row[1][1] - row[2][2]) * 2.0;
      quaternion = [
        0.25 * s,
        (row[0][1] + row[1][0]) / s,
        (row[0][2] + row[2][0]) / s,
        (row[2][1] - row[1][2]) / s
      ];
    } else if (row[1][1] > row[2][2]) {
      s = Math.sqrt(1.0 + row[1][1] - row[0][0] - row[2][2]) * 2.0;
      quaternion = [
        (row[0][1] + row[1][0]) / s,
        0.25 * s,
        (row[1][2] + row[2][1]) / s,
        (row[0][2] - row[2][0]) / s
      ];
    } else {
      s = Math.sqrt(1.0 + row[2][2] - row[0][0] - row[1][1]) * 2.0;
      quaternion = [
        (row[0][2] + row[2][0]) / s,
        (row[1][2] + row[2][1]) / s,
        0.25 * s,
        (row[1][0] - row[0][1]) / s
      ];
    }

    return {
      translate: translate, scale: scale, skew: skew,
      quaternion: quaternion, perspective: perspective
    };
  }
  return decomposeMatrix;
})();

function dot(v1, v2) {
  var result = 0;
  for (var i = 0; i < v1.length; i++) {
    result += v1[i] * v2[i];
  }
  return result;
}

function multiplyMatrices(a, b) {
  return [
    a[0] * b[0] + a[4] * b[1] + a[8] * b[2] + a[12] * b[3],
    a[1] * b[0] + a[5] * b[1] + a[9] * b[2] + a[13] * b[3],
    a[2] * b[0] + a[6] * b[1] + a[10] * b[2] + a[14] * b[3],
    a[3] * b[0] + a[7] * b[1] + a[11] * b[2] + a[15] * b[3],

    a[0] * b[4] + a[4] * b[5] + a[8] * b[6] + a[12] * b[7],
    a[1] * b[4] + a[5] * b[5] + a[9] * b[6] + a[13] * b[7],
    a[2] * b[4] + a[6] * b[5] + a[10] * b[6] + a[14] * b[7],
    a[3] * b[4] + a[7] * b[5] + a[11] * b[6] + a[15] * b[7],

    a[0] * b[8] + a[4] * b[9] + a[8] * b[10] + a[12] * b[11],
    a[1] * b[8] + a[5] * b[9] + a[9] * b[10] + a[13] * b[11],
    a[2] * b[8] + a[6] * b[9] + a[10] * b[10] + a[14] * b[11],
    a[3] * b[8] + a[7] * b[9] + a[11] * b[10] + a[15] * b[11],

    a[0] * b[12] + a[4] * b[13] + a[8] * b[14] + a[12] * b[15],
    a[1] * b[12] + a[5] * b[13] + a[9] * b[14] + a[13] * b[15],
    a[2] * b[12] + a[6] * b[13] + a[10] * b[14] + a[14] * b[15],
    a[3] * b[12] + a[7] * b[13] + a[11] * b[14] + a[15] * b[15]
  ];
}

function convertItemToMatrix(item) {
  switch (item.t) {
    case 'rotateX':
      var angle = item.d * Math.PI / 180;
      return [1, 0, 0, 0,
              0, Math.cos(angle), Math.sin(angle), 0,
              0, -Math.sin(angle), Math.cos(angle), 0,
              0, 0, 0, 1];
    case 'rotateY':
      var angle = item.d * Math.PI / 180;
      return [Math.cos(angle), 0, -Math.sin(angle), 0,
              0, 1, 0, 0,
              Math.sin(angle), 0, Math.cos(angle), 0,
              0, 0, 0, 1];
    case 'rotate':
    case 'rotateZ':
      var angle = item.d * Math.PI / 180;
      return [Math.cos(angle), Math.sin(angle), 0, 0,
              -Math.sin(angle), Math.cos(angle), 0, 0,
              0, 0, 1, 0,
              0, 0, 0, 1];
    case 'rotate3d':
      var x = item.d[0];
      var y = item.d[1];
      var z = item.d[2];
      var sqrLength = x * x + y * y + z * z;
      if (sqrLength === 0) {
        x = 1;
        y = 0;
        z = 0;
      } else if (sqrLength !== 1) {
        var length = Math.sqrt(sqrLength);
        x /= length;
        y /= length;
        z /= length;
      }
      var s = Math.sin(item.d[3] * Math.PI / 360);
      var sc = s * Math.cos(item.d[3] * Math.PI / 360);
      var sq = s * s;
      return [
        1 - 2 * (y * y + z * z) * sq,
        2 * (x * y * sq + z * sc),
        2 * (x * z * sq - y * sc),
        0,

        2 * (x * y * sq - z * sc),
        1 - 2 * (x * x + z * z) * sq,
        2 * (y * z * sq + x * sc),
        0,

        2 * (x * z * sq + y * sc),
        2 * (y * z * sq - x * sc),
        1 - 2 * (x * x + y * y) * sq,
        0,

        0, 0, 0, 1
      ];
    case 'scale':
      return [item.d[0], 0, 0, 0,
              0, item.d[1], 0, 0,
              0, 0, 1, 0,
              0, 0, 0, 1];
    case 'scale3d':
      return [item.d[0], 0, 0, 0,
              0, item.d[1], 0, 0,
              0, 0, item.d[2], 0,
              0, 0, 0, 1];
    case 'skew':
      return [1, Math.tan(item.d[1] * Math.PI / 180), 0, 0,
              Math.tan(item.d[0] * Math.PI / 180), 1, 0, 0,
              0, 0, 1, 0,
              0, 0, 0, 1];
    case 'skewX':
      return [1, 0, 0, 0,
              Math.tan(item.d * Math.PI / 180), 1, 0, 0,
              0, 0, 1, 0,
              0, 0, 0, 1];
    case 'skewY':
      return [1, Math.tan(item.d * Math.PI / 180), 0, 0,
              0, 1, 0, 0,
              0, 0, 1, 0,
              0, 0, 0, 1];
    // TODO: Work out what to do with non-px values.
    case 'translate':
      return [1, 0, 0, 0,
              0, 1, 0, 0,
              0, 0, 1, 0,
              item.d[0].px, item.d[1].px, 0, 1];
    case 'translate3d':
      return [1, 0, 0, 0,
              0, 1, 0, 0,
              0, 0, 1, 0,
              item.d[0].px, item.d[1].px, item.d[2].px, 1];
    case 'perspective':
      return [
        1, 0, 0, 0,
        0, 1, 0, 0,
        0, 0, 1, -1 / item.d.px,
        0, 0, 0, 1];
    case 'matrix':
      return [item.d[0], item.d[1], 0, 0,
              item.d[2], item.d[3], 0, 0,
              0, 0, 1, 0,
              item.d[4], item.d[5], 0, 1];
    case 'matrix3d':
      return item.d;
    default:
      ASSERT_ENABLED && assert(false, 'Transform item type ' + item.t +
          ' conversion to matrix not yet implemented.');
  }
}

function convertToMatrix(transformList) {
  if (transformList.length === 0) {
    return [1, 0, 0, 0,
            0, 1, 0, 0,
            0, 0, 1, 0,
            0, 0, 0, 1];
  }
  return transformList.map(convertItemToMatrix).reduce(multiplyMatrices);
}

var composeMatrix = (function() {
  function multiply(a, b) {
    var result = [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]];
    for (var i = 0; i < 4; i++) {
      for (var j = 0; j < 4; j++) {
        for (var k = 0; k < 4; k++) {
          result[i][j] += b[i][k] * a[k][j];
        }
      }
    }
    return result;
  }

  function is2D(m) {
    return (
        m[0][2] == 0 &&
        m[0][3] == 0 &&
        m[1][2] == 0 &&
        m[1][3] == 0 &&
        m[2][0] == 0 &&
        m[2][1] == 0 &&
        m[2][2] == 1 &&
        m[2][3] == 0 &&
        m[3][2] == 0 &&
        m[3][3] == 1);
  }

  function composeMatrix(translate, scale, skew, quat, perspective) {
    var matrix = [[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]];

    for (var i = 0; i < 4; i++) {
      matrix[i][3] = perspective[i];
    }

    for (var i = 0; i < 3; i++) {
      for (var j = 0; j < 3; j++) {
        matrix[3][i] += translate[j] * matrix[j][i];
      }
    }

    var x = quat[0], y = quat[1], z = quat[2], w = quat[3];

    var rotMatrix = [[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]];

    rotMatrix[0][0] = 1 - 2 * (y * y + z * z);
    rotMatrix[0][1] = 2 * (x * y - z * w);
    rotMatrix[0][2] = 2 * (x * z + y * w);
    rotMatrix[1][0] = 2 * (x * y + z * w);
    rotMatrix[1][1] = 1 - 2 * (x * x + z * z);
    rotMatrix[1][2] = 2 * (y * z - x * w);
    rotMatrix[2][0] = 2 * (x * z - y * w);
    rotMatrix[2][1] = 2 * (y * z + x * w);
    rotMatrix[2][2] = 1 - 2 * (x * x + y * y);

    matrix = multiply(matrix, rotMatrix);

    var temp = [[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]];
    if (skew[2]) {
      temp[2][1] = skew[2];
      matrix = multiply(matrix, temp);
    }

    if (skew[1]) {
      temp[2][1] = 0;
      temp[2][0] = skew[0];
      matrix = multiply(matrix, temp);
    }

    if (skew[0]) {
      temp[2][0] = 0;
      temp[1][0] = skew[0];
      matrix = multiply(matrix, temp);
    }

    for (var i = 0; i < 3; i++) {
      for (var j = 0; j < 3; j++) {
        matrix[i][j] *= scale[i];
      }
    }

    if (is2D(matrix)) {
      return {
        t: 'matrix',
        d: [matrix[0][0], matrix[0][1], matrix[1][0], matrix[1][1],
            matrix[3][0], matrix[3][1]]
      };
    }
    return {
      t: 'matrix3d',
      d: matrix[0].concat(matrix[1], matrix[2], matrix[3])
    };
  }
  return composeMatrix;
})();

function interpolateDecomposedTransformsWithMatrices(fromM, toM, f) {
  var product = dot(fromM.quaternion, toM.quaternion);
  product = clamp(product, -1.0, 1.0);

  var quat = [];
  if (product === 1.0) {
    quat = fromM.quaternion;
  } else {
    var theta = Math.acos(product);
    var w = Math.sin(f * theta) * 1 / Math.sqrt(1 - product * product);

    for (var i = 0; i < 4; i++) {
      quat.push(fromM.quaternion[i] * (Math.cos(f * theta) - product * w) +
                toM.quaternion[i] * w);
    }
  }

  var translate = interp(fromM.translate, toM.translate, f);
  var scale = interp(fromM.scale, toM.scale, f);
  var skew = interp(fromM.skew, toM.skew, f);
  var perspective = interp(fromM.perspective, toM.perspective, f);

  return composeMatrix(translate, scale, skew, quat, perspective);
}

function interpTransformValue(from, to, f) {
  var type = from.t ? from.t : to.t;
  switch (type) {
    case 'matrix':
    case 'matrix3d':
      ASSERT_ENABLED && assert(false,
          'Must use matrix decomposition when interpolating raw matrices');
    // Transforms with unitless parameters.
    case 'rotate':
    case 'rotateX':
    case 'rotateY':
    case 'rotateZ':
    case 'rotate3d':
    case 'scale':
    case 'scaleX':
    case 'scaleY':
    case 'scaleZ':
    case 'scale3d':
    case 'skew':
    case 'skewX':
    case 'skewY':
      return {t: type, d: interp(from.d, to.d, f, type)};
    default:
      // Transforms with lengthType parameters.
      var result = [];
      var maxVal;
      if (from.d && to.d) {
        maxVal = Math.max(from.d.length, to.d.length);
      } else if (from.d) {
        maxVal = from.d.length;
      } else {
        maxVal = to.d.length;
      }
      for (var j = 0; j < maxVal; j++) {
        var fromVal = from.d ? from.d[j] : {};
        var toVal = to.d ? to.d[j] : {};
        result.push(lengthType.interpolate(fromVal, toVal, f));
      }
      return {t: type, d: result};
  }
}

function isMatrix(item) {
  return item.t[0] === 'm';
}

// The CSSWG decided to disallow scientific notation in CSS property strings
// (see http://lists.w3.org/Archives/Public/www-style/2010Feb/0050.html).
// We need this function to hakonitize all numbers before adding them to
// property strings.
// TODO: Apply this function to all property strings
function n(num) {
  return Number(num).toFixed(4);
}

var transformType = {
  add: function(base, delta) { return base.concat(delta); },
  interpolate: function(from, to, f) {
    var out = [];
    for (var i = 0; i < Math.min(from.length, to.length); i++) {
      if (from[i].t !== to[i].t || isMatrix(from[i])) {
        break;
      }
      out.push(interpTransformValue(from[i], to[i], f));
    }

    if (i < Math.min(from.length, to.length) ||
        from.some(isMatrix) || to.some(isMatrix)) {
      if (from.decompositionPair !== to) {
        from.decompositionPair = to;
        from.decomposition = decomposeMatrix(convertToMatrix(from.slice(i)));
      }
      if (to.decompositionPair !== from) {
        to.decompositionPair = from;
        to.decomposition = decomposeMatrix(convertToMatrix(to.slice(i)));
      }
      out.push(interpolateDecomposedTransformsWithMatrices(
          from.decomposition, to.decomposition, f));
      return out;
    }

    for (; i < from.length; i++) {
      out.push(interpTransformValue(from[i], {t: null, d: null}, f));
    }
    for (; i < to.length; i++) {
      out.push(interpTransformValue({t: null, d: null}, to[i], f));
    }
    return out;
  },
  toCssValue: function(value, svgMode) {
    // TODO: fix this :)
    var out = '';
    for (var i = 0; i < value.length; i++) {
      ASSERT_ENABLED && assert(
          value[i].t, 'transform type should be resolved by now');
      switch (value[i].t) {
        case 'rotate':
        case 'rotateX':
        case 'rotateY':
        case 'rotateZ':
        case 'skewX':
        case 'skewY':
          var unit = svgMode ? '' : 'deg';
          out += value[i].t + '(' + value[i].d + unit + ') ';
          break;
        case 'skew':
          var unit = svgMode ? '' : 'deg';
          out += value[i].t + '(' + value[i].d[0] + unit;
          if (value[i].d[1] === 0) {
            out += ') ';
          } else {
            out += ', ' + value[i].d[1] + unit + ') ';
          }
          break;
        case 'rotate3d':
          var unit = svgMode ? '' : 'deg';
          out += value[i].t + '(' + value[i].d[0] + ', ' + value[i].d[1] +
              ', ' + value[i].d[2] + ', ' + value[i].d[3] + unit + ') ';
          break;
        case 'translateX':
        case 'translateY':
        case 'translateZ':
        case 'perspective':
          out += value[i].t + '(' + lengthType.toCssValue(value[i].d[0]) +
              ') ';
          break;
        case 'translate':
          if (svgMode) {
            if (value[i].d[1] === undefined) {
              out += value[i].t + '(' + value[i].d[0].px + ') ';
            } else {
              out += (
                  value[i].t + '(' + value[i].d[0].px + ', ' +
                  value[i].d[1].px + ') ');
            }
            break;
          }
          if (value[i].d[1] === undefined) {
            out += value[i].t + '(' + lengthType.toCssValue(value[i].d[0]) +
                ') ';
          } else {
            out += value[i].t + '(' + lengthType.toCssValue(value[i].d[0]) +
                ', ' + lengthType.toCssValue(value[i].d[1]) + ') ';
          }
          break;
        case 'translate3d':
          var values = value[i].d.map(lengthType.toCssValue);
          out += value[i].t + '(' + values[0] + ', ' + values[1] +
              ', ' + values[2] + ') ';
          break;
        case 'scale':
          if (value[i].d[0] === value[i].d[1]) {
            out += value[i].t + '(' + value[i].d[0] + ') ';
          } else {
            out += value[i].t + '(' + value[i].d[0] + ', ' + value[i].d[1] +
                ') ';
          }
          break;
        case 'scaleX':
        case 'scaleY':
        case 'scaleZ':
          out += value[i].t + '(' + value[i].d[0] + ') ';
          break;
        case 'scale3d':
          out += value[i].t + '(' + value[i].d[0] + ', ' +
              value[i].d[1] + ', ' + value[i].d[2] + ') ';
          break;
        case 'matrix':
        case 'matrix3d':
          out += value[i].t + '(' + value[i].d.map(n).join(', ') + ') ';
          break;
      }
    }
    return out.substring(0, out.length - 1);
  },
  fromCssValue: function(value) {
    // TODO: fix this :)
    if (value === undefined) {
      return undefined;
    }
    var result = [];
    while (value.length > 0) {
      var r;
      for (var i = 0; i < transformREs.length; i++) {
        var reSpec = transformREs[i];
        r = reSpec[0].exec(value);
        if (r) {
          result.push({t: reSpec[2], d: reSpec[1](r)});
          value = value.substring(r[0].length);
          break;
        }
      }
      if (!isDefinedAndNotNull(r)) {
        return result;
      }
    }
    return result;
  }
};

function interpolateFlag(prev, next, frac) {
  var flag = (frac >= 0.5) ? next : prev;
  return flag ? 1 : 0;
}

var pathType = {
  add: function() { throw 'Addition not supported for path attribute' },
  interpolate: function(from, to, f) {
    // SVG's path interpolation is specified in
    // http://www.w3.org/TR/SVG/paths.html#DAttribute

    var fromSegList = from.path.pathSegList;
    var toSegList = to.path.pathSegList;
    var numItems = fromSegList.numberOfItems;
    if (numItems !== toSegList.numberOfItems) {
      // Inconsistent # items, so we cannot interpolate
      return from;
    }

    var value = '';
    for (var index = 0; index < numItems; ++index) {
      var fromSegment = fromSegList.getItem(index);
      var toSegment = toSegList.getItem(index);
      if (fromSegment.pathSegType !== toSegment.pathSegType) {
        // Inconsistent segment type, so we cannot interpolate
        return from;
      }

      // pathSegType takes the values listed in
      // http://www.w3.org/TR/SVG/paths.html#InterfaceSVGPathSeg
      switch (fromSegment.pathSegType) {
        case SVGPathSeg.PATHSEG_CLOSEPATH:
          value += ' Z ';
          break;
        case SVGPathSeg.PATHSEG_MOVETO_ABS:
          value += ' M ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_MOVETO_REL:
          value += ' m ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_LINETO_ABS:
          value += ' L ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_LINETO_REL:
          value += ' l ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_CUBIC_ABS:
          value += ' C ' + interp(fromSegment.x1, toSegment.x1, f) +
              ' ' + interp(fromSegment.y1, toSegment.y1, f) +
              ' ' + interp(fromSegment.x2, toSegment.x2, f) +
              ' ' + interp(fromSegment.y2, toSegment.y2, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_CUBIC_REL:
          value += ' c ' + interp(fromSegment.x1, toSegment.x1, f) +
              ' ' + interp(fromSegment.y1, toSegment.y1, f) +
              ' ' + interp(fromSegment.x2, toSegment.x2, f) +
              ' ' + interp(fromSegment.y2, toSegment.y2, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_QUADRATIC_ABS:
          value += ' Q ' + interp(fromSegment.x1, toSegment.x1, f) +
              ' ' + interp(fromSegment.y1, toSegment.y1, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_QUADRATIC_REL:
          value += ' q ' + interp(fromSegment.x1, toSegment.x1, f) +
              ' ' + interp(fromSegment.y1, toSegment.y1, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case fromSegment.PATHSEG_ARC_ABS:
          value += ' A ' + interp(fromSegment.r1, toSegment.r1, f) +
              ' ' + interp(fromSegment.r2, toSegment.r2, f) +
              ' ' + interp(fromSegment.angle, toSegment.angle, f) +
              ' ' + interpolateFlag(fromSegment.largeArcFlag,
                                    toSegment.largeArcFlag, f) +
              ' ' + interpolateFlag(fromSegment.sweepFlag,
                                    toSegment.sweepFlag, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case fromSegment.PATHSEG_ARC_REL:
          value += ' a ' + interp(fromSegment.r1, toSegment.r1, f) +
              ' ' + interp(fromSegment.r2, toSegment.r2, f) +
              ' ' + interp(fromSegment.angle, toSegment.angle, f) +
              ' ' + interpolateFlag(fromSegment.largeArcFlag,
                                    toSegment.largeArcFlag, f) +
              ' ' + interpolateFlag(fromSegment.sweepFlag,
                                    toSegment.sweepFlag, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_LINETO_HORIZONTAL_ABS:
          value += ' H ' + interp(fromSegment.x, toSegment.x, f);
          break;
        case SVGPathSeg.PATHSEG_LINETO_HORIZONTAL_REL:
          value += ' h ' + interp(fromSegment.x, toSegment.x, f);
          break;
        case SVGPathSeg.PATHSEG_LINETO_VERTICAL_ABS:
          value += ' V ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_LINETO_VERTICAL_REL:
          value += ' v ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_CUBIC_SMOOTH_ABS:
          value += ' S ' + interp(fromSegment.x2, toSegment.x2, f) +
              ' ' + interp(fromSegment.y2, toSegment.y2, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_CUBIC_SMOOTH_REL:
          value += ' s ' + interp(fromSegment.x2, toSegment.x2, f) +
              ' ' + interp(fromSegment.y2, toSegment.y2, f) +
              ' ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS:
          value += ' T ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        case SVGPathSeg.PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL:
          value += ' t ' + interp(fromSegment.x, toSegment.x, f) +
              ' ' + interp(fromSegment.y, toSegment.y, f);
          break;
        default:
          // Unknown segment type, so we cannot interpolate
          return from;
      }
    }

    var path = document.createElementNS('http://www.w3.org/2000/svg', 'path');
    path.setAttribute('d', value.trim());
    return {path: path};
  },
  toCssValue: function(value, svgMode) {
    ASSERT_ENABLED && assert(svgMode,
        'Path type should only be used with SVG \'d\' attribute');
    return value.path.getAttribute('d');
  },
  fromCssValue: function(value) {
    var path = document.createElementNS('http://www.w3.org/2000/svg', 'path');
    if (value)
      path.setAttribute('d', value);
    return {path: path};
  }
};

var propertyTypes = {
  azimuth: numberType,
  backgroundColor: colorType,
  backgroundPosition: positionListType,
  borderBottomColor: colorType,
  borderBottomLeftRadius: percentLengthType,
  borderBottomRightRadius: percentLengthType,
  borderBottomWidth: lengthType,
  borderLeftColor: colorType,
  borderLeftWidth: lengthType,
  borderRightColor: colorType,
  borderRightWidth: lengthType,
  borderSpacing: lengthType,
  borderTopColor: colorType,
  borderTopLeftRadius: percentLengthType,
  borderTopRightRadius: percentLengthType,
  borderTopWidth: lengthType,
  bottom: percentLengthAutoType,
  boxShadow: shadowType,
  clip: typeWithKeywords(['auto'], rectangleType),
  color: colorType,
  cx: lengthType,
  cy: lengthType,
  d: pathType,
  display: typeWithKeywords([
    'inline',
    'block',
    'list-item',
    'run-in',
    'compact',
    'marker',
    'table',
    'inline-table',
    'table-row-group',
    'table-header-group',
    'table-footer-group',
    'table-row',
    'table-column-group',
    'table-column',
    'table-cell',
    'table-caption',
    'none'
  ], nonNumericType),
  dx: percentLengthListType, // should be lengthListType
  dy: percentLengthListType, // should be lengthListType
  elevation: numberType,
  fill: colorType,
  'fill-opacity': numberType,
  'flood-color': colorType,
  'flood-opacity': numberType,

  // TODO: Handle these keywords properly.
  fontSize: typeWithKeywords(['smaller', 'larger'], percentLengthType),
  fontWeight: typeWithKeywords(['lighter', 'bolder'], fontWeightType),

  height: percentLengthAutoType,
  k1: numberType,
  k2: numberType,
  k3: numberType,
  k4: numberType,
  left: percentLengthAutoType,
  letterSpacing: typeWithKeywords(['normal'], lengthType),
  'lighting-color': colorType,
  limitingConeAngle: numberType,
  lineHeight: percentLengthType, // TODO: Should support numberType as well.
  marginBottom: lengthAutoType,
  marginLeft: lengthAutoType,
  marginRight: lengthAutoType,
  marginTop: lengthAutoType,
  maxHeight: typeWithKeywords(
      ['none', 'max-content', 'min-content', 'fill-available', 'fit-content'],
      percentLengthType),
  maxWidth: typeWithKeywords(
      ['none', 'max-content', 'min-content', 'fill-available', 'fit-content'],
      percentLengthType),
  minHeight: typeWithKeywords(
      ['max-content', 'min-content', 'fill-available', 'fit-content'],
      percentLengthType),
  minWidth: typeWithKeywords(
      ['max-content', 'min-content', 'fill-available', 'fit-content'],
      percentLengthType),
  offset: percentLengthType,
  opacity: numberType,
  outlineColor: typeWithKeywords(['invert'], colorType),
  outlineOffset: lengthType,
  outlineWidth: lengthType,
  paddingBottom: lengthType,
  paddingLeft: lengthType,
  paddingRight: lengthType,
  paddingTop: lengthType,
  perspective: typeWithKeywords(['none'], lengthType),
  perspectiveOrigin: originType,
  points: numberListType,
  pointsAtX: numberType,
  pointsAtY: numberType,
  pointsAtZ: numberType,
  r: lengthType,
  refX: lengthType,
  refY: lengthType,
  rotate: numberListType,
  rx: lengthType,
  ry: lengthType,
  right: percentLengthAutoType,
  scale: numberType,
  startOffset: lengthType,
  'stop-color': colorType,
  'stop-opacity': numberType,
  stdDeviation: numberListType, // 1 or 2 numbers
  stroke: colorType,
  'stroke-dasharray': percentLengthListType,
  'stroke-dashoffset': percentLengthType,
  'stroke-opacity': numberType,
  'stroke-width': percentLengthType,
  textIndent: typeWithKeywords(['each-line', 'hanging'], percentLengthType),
  textShadow: shadowType,
  top: percentLengthAutoType,
  transform: transformType,
  transformOrigin: originType,
  values: numberListType,
  verticalAlign: typeWithKeywords([
    'baseline',
    'sub',
    'super',
    'text-top',
    'text-bottom',
    'middle',
    'top',
    'bottom'
  ], percentLengthType),
  visibility: visibilityType,
  width: typeWithKeywords([
    'border-box',
    'content-box',
    'auto',
    'max-content',
    'min-content',
    'available',
    'fit-content'
  ], percentLengthType),
  wordSpacing: typeWithKeywords(['normal'], percentLengthType),
  x: percentLengthListType,
  x1: lengthType,
  x2: lengthType,
  y: percentLengthListType,
  y1: lengthType,
  y2: lengthType,
  z: lengthType,
  zIndex: typeWithKeywords(['auto'], integerType)
};

var svgProperties = {
  'azimuth': 1,
  'color': 1,
  'cx': 1,
  'cy': 1,
  'd': 1,
  'dx': 1,
  'dy': 1,
  'elevation': 1,
  'fill': 1,
  'fill-opacity': 1,
  'flood-color': 1,
  'flood-opacity': 1,
  'height': 1,
  'k1': 1,
  'k2': 1,
  'k3': 1,
  'k4': 1,
  'lighting-color': 1,
  'limitingConeAngle': 1,
  'offset': 1,
  'points': 1,
  'pointsAtX': 1,
  'pointsAtY': 1,
  'pointsAtZ': 1,
  'r': 1,
  'refX': 1,
  'refY': 1,
  'rotate': 1,
  'rx': 1,
  'ry': 1,
  'scale': 1,
  'startOffset': 1,
  'stdDeviation': 1,
  'stop-color': 1,
  'stop-opacity': 1,
  'stroke': 1,
  'stroke-dasharray': 1,
  'stroke-dashoffset': 1,
  'stroke-opacity': 1,
  'stroke-width': 1,
  'transform': 1,
  'values': 1,
  'width': 1,
  'x': 1,
  'x1': 1,
  'x2': 1,
  'y': 1,
  'y1': 1,
  'y2': 1,
  'z': 1
};

var borderWidthAliases = {
  initial: '3px',
  thin: '1px',
  medium: '3px',
  thick: '5px'
};

var propertyValueAliases = {
  backgroundColor: { initial: 'transparent' },
  backgroundPosition: { initial: '0% 0%' },
  borderBottomColor: { initial: 'currentColor' },
  borderBottomLeftRadius: { initial: '0px' },
  borderBottomRightRadius: { initial: '0px' },
  borderBottomWidth: borderWidthAliases,
  borderLeftColor: { initial: 'currentColor' },
  borderLeftWidth: borderWidthAliases,
  borderRightColor: { initial: 'currentColor' },
  borderRightWidth: borderWidthAliases,
  // Spec says this should be 0 but in practise it is 2px.
  borderSpacing: { initial: '2px' },
  borderTopColor: { initial: 'currentColor' },
  borderTopLeftRadius: { initial: '0px' },
  borderTopRightRadius: { initial: '0px' },
  borderTopWidth: borderWidthAliases,
  bottom: { initial: 'auto' },
  clip: { initial: 'rect(0px, 0px, 0px, 0px)' },
  color: { initial: 'black' }, // Depends on user agent.
  fontSize: {
    initial: '100%',
    'xx-small': '60%',
    'x-small': '75%',
    'small': '89%',
    'medium': '100%',
    'large': '120%',
    'x-large': '150%',
    'xx-large': '200%'
  },
  fontWeight: {
    initial: '400',
    normal: '400',
    bold: '700'
  },
  height: { initial: 'auto' },
  left: { initial: 'auto' },
  letterSpacing: { initial: 'normal' },
  lineHeight: {
    initial: '120%',
    normal: '120%'
  },
  marginBottom: { initial: '0px' },
  marginLeft: { initial: '0px' },
  marginRight: { initial: '0px' },
  marginTop: { initial: '0px' },
  maxHeight: { initial: 'none' },
  maxWidth: { initial: 'none' },
  minHeight: { initial: '0px' },
  minWidth: { initial: '0px' },
  opacity: { initial: '1.0' },
  outlineColor: { initial: 'invert' },
  outlineOffset: { initial: '0px' },
  outlineWidth: borderWidthAliases,
  paddingBottom: { initial: '0px' },
  paddingLeft: { initial: '0px' },
  paddingRight: { initial: '0px' },
  paddingTop: { initial: '0px' },
  right: { initial: 'auto' },
  textIndent: { initial: '0px' },
  textShadow: {
    initial: '0px 0px 0px transparent',
    none: '0px 0px 0px transparent'
  },
  top: { initial: 'auto' },
  transform: {
    initial: '',
    none: ''
  },
  verticalAlign: { initial: '0px' },
  visibility: { initial: 'visible' },
  width: { initial: 'auto' },
  wordSpacing: { initial: 'normal' },
  zIndex: { initial: 'auto' }
};

var propertyIsSVGAttrib = function(property, target) {
  return target.namespaceURI === 'http://www.w3.org/2000/svg' &&
      property in svgProperties;
};

var getType = function(property) {
  return propertyTypes[property] || nonNumericType;
};

var add = function(property, base, delta) {
  if (delta === rawNeutralValue) {
    return base;
  }
  if (base === 'inherit' || delta === 'inherit') {
    return nonNumericType.add(base, delta);
  }
  return getType(property).add(base, delta);
};


/**
 * Interpolate the given property name (f*100)% of the way from 'from' to 'to'.
 * 'from' and 'to' are both raw values already converted from CSS value
 * strings. Requires the target element to be able to determine whether the
 * given property is an SVG attribute or not, as this impacts the conversion of
 * the interpolated value back into a CSS value string for transform
 * translations.
 *
 * e.g. interpolate('transform', elem, 'rotate(40deg)', 'rotate(50deg)', 0.3);
 *   will return 'rotate(43deg)'.
 */
var interpolate = function(property, from, to, f) {
  ASSERT_ENABLED && assert(
      isDefinedAndNotNull(from) && isDefinedAndNotNull(to),
      'Both to and from values should be specified for interpolation');
  if (from === 'inherit' || to === 'inherit') {
    return nonNumericType.interpolate(from, to, f);
  }
  if (f === 0) {
    return from;
  }
  if (f === 1) {
    return to;
  }
  return getType(property).interpolate(from, to, f);
};


/**
 * Convert the provided interpolable value for the provided property to a CSS
 * value string. Note that SVG transforms do not require units for translate
 * or rotate values while CSS properties require 'px' or 'deg' units.
 */
var toCssValue = function(property, value, svgMode) {
  if (value === 'inherit') {
    return value;
  }
  return getType(property).toCssValue(value, svgMode);
};

var fromCssValue = function(property, value) {
  if (value === cssNeutralValue) {
    return rawNeutralValue;
  }
  if (value === 'inherit') {
    return value;
  }
  if (property in propertyValueAliases &&
      value in propertyValueAliases[property]) {
    value = propertyValueAliases[property][value];
  }
  var result = getType(property).fromCssValue(value);
  // Currently we'll hit this assert if input to the API is bad. To avoid this,
  // we should eliminate invalid values when normalizing the list of keyframes.
  // See the TODO in isSupportedPropertyValue().
  ASSERT_ENABLED && assert(isDefinedAndNotNull(result),
      'Invalid property value "' + value + '" for property "' + property + '"');
  return result;
};

// Sentinel values
var cssNeutralValue = {};
var rawNeutralValue = {};



/** @constructor */
var CompositableValue = function() {
};

CompositableValue.prototype = {
  compositeOnto: abstractMethod,
  // This is purely an optimization.
  dependsOnUnderlyingValue: function() {
    return true;
  }
};



/** @constructor */
var AddReplaceCompositableValue = function(value, composite) {
  this.value = value;
  this.composite = composite;
  ASSERT_ENABLED && assert(
      !(this.value === cssNeutralValue && this.composite === 'replace'),
      'Should never replace-composite the neutral value');
};

AddReplaceCompositableValue.prototype = createObject(
    CompositableValue.prototype, {
      compositeOnto: function(property, underlyingValue) {
        switch (this.composite) {
          case 'replace':
            return this.value;
          case 'add':
            return add(property, underlyingValue, this.value);
          default:
            ASSERT_ENABLED && assert(
                false, 'Invalid composite operation ' + this.composite);
        }
      },
      dependsOnUnderlyingValue: function() {
        return this.composite === 'add';
      }
    });



/** @constructor */
var BlendedCompositableValue = function(startValue, endValue, fraction) {
  this.startValue = startValue;
  this.endValue = endValue;
  this.fraction = fraction;
};

BlendedCompositableValue.prototype = createObject(
    CompositableValue.prototype, {
      compositeOnto: function(property, underlyingValue) {
        return interpolate(property,
            this.startValue.compositeOnto(property, underlyingValue),
            this.endValue.compositeOnto(property, underlyingValue),
            this.fraction);
      },
      dependsOnUnderlyingValue: function() {
        // Travis crashes here randomly in Chrome beta and unstable,
        // this try catch is to help debug the problem.
        try {
          return this.startValue.dependsOnUnderlyingValue() ||
              this.endValue.dependsOnUnderlyingValue();
        }
        catch (error) {
          throw new Error(
              error + '\n JSON.stringify(this) = ' + JSON.stringify(this));
        }
      }
    });

/** @constructor */
var CompositedPropertyMap = function(target) {
  this.properties = {};
  this.baseValues = {};
  this.target = target;
};

CompositedPropertyMap.prototype = {
  addValue: function(property, animValue) {
    if (!(property in this.properties)) {
      this.properties[property] = [];
    }
    if (!(animValue instanceof CompositableValue)) {
      throw new TypeError('expected CompositableValue');
    }
    this.properties[property].push(animValue);
  },
  stackDependsOnUnderlyingValue: function(stack) {
    for (var i = 0; i < stack.length; i++) {
      if (!stack[i].dependsOnUnderlyingValue()) {
        return false;
      }
    }
    return true;
  },
  clear: function() {
    for (var property in this.properties) {
      if (this.stackDependsOnUnderlyingValue(this.properties[property])) {
        clearValue(this.target, property);
      }
    }
  },
  captureBaseValues: function() {
    for (var property in this.properties) {
      var stack = this.properties[property];
      if (stack.length > 0 && this.stackDependsOnUnderlyingValue(stack)) {
        var baseValue = fromCssValue(property, getValue(this.target, property));
        // TODO: Decide what to do with elements not in the DOM.
        ASSERT_ENABLED && assert(
            isDefinedAndNotNull(baseValue) && baseValue !== '',
            'Base value should always be set. ' +
            'Is the target element in the DOM?');
        this.baseValues[property] = baseValue;
      } else {
        this.baseValues[property] = undefined;
      }
    }
  },
  applyAnimatedValues: function() {
    for (var property in this.properties) {
      var valuesToComposite = this.properties[property];
      if (valuesToComposite.length === 0) {
        continue;
      }
      var baseValue = this.baseValues[property];
      var i = valuesToComposite.length - 1;
      while (i > 0 && valuesToComposite[i].dependsOnUnderlyingValue()) {
        i--;
      }
      for (; i < valuesToComposite.length; i++) {
        baseValue = valuesToComposite[i].compositeOnto(property, baseValue);
      }
      ASSERT_ENABLED && assert(
          isDefinedAndNotNull(baseValue) && baseValue !== '',
          'Value should always be set after compositing');
      var isSvgMode = propertyIsSVGAttrib(property, this.target);
      setValue(this.target, property, toCssValue(property, baseValue,
          isSvgMode));
      this.properties[property] = [];
    }
  }
};


var cssStyleDeclarationAttribute = {
  cssText: true,
  length: true,
  parentRule: true,
  'var': true
};

var cssStyleDeclarationMethodModifiesStyle = {
  getPropertyValue: false,
  getPropertyCSSValue: false,
  removeProperty: true,
  getPropertyPriority: false,
  setProperty: true,
  item: false
};

var copyInlineStyle = function(sourceStyle, destinationStyle) {
  for (var i = 0; i < sourceStyle.length; i++) {
    var property = sourceStyle[i];
    destinationStyle[property] = sourceStyle[property];
  }
};

var retickThenGetComputedStyle = function() {
  repeatLastTick();
  ensureOriginalGetComputedStyle();
  return window.getComputedStyle.apply(this, arguments);
};

// This redundant flag is to support Safari which has trouble determining
// function object equality during an animation.
var isGetComputedStylePatched = false;
var originalGetComputedStyle = window.getComputedStyle;

var ensureRetickBeforeGetComputedStyle = function() {
  if (!isGetComputedStylePatched) {
    Object.defineProperty(window, 'getComputedStyle', configureDescriptor({
      value: retickThenGetComputedStyle
    }));
    isGetComputedStylePatched = true;
  }
};

var ensureOriginalGetComputedStyle = function() {
  if (isGetComputedStylePatched) {
    Object.defineProperty(window, 'getComputedStyle', configureDescriptor({
      value: originalGetComputedStyle
    }));
    isGetComputedStylePatched = false;
  }
};

// Changing the inline style of an element under animation may require the
// animation to be recomputed ontop of the new inline style if
// getComputedStyle() is called inbetween setting the style and the next
// animation frame.
// We modify getComputedStyle() to re-evaluate the animations only if it is
// called instead of re-evaluating them here potentially unnecessarily.
var animatedInlineStyleChanged = function() {
  maybeRestartAnimation();
  ensureRetickBeforeGetComputedStyle();
};



/** @constructor */
var AnimatedCSSStyleDeclaration = function(element) {
  ASSERT_ENABLED && assert(
      !(element.style instanceof AnimatedCSSStyleDeclaration),
      'Element must not already have an animated style attached.');

  // Stores the inline style of the element on its behalf while the
  // polyfill uses the element's inline style to simulate web animations.
  // This is needed to fake regular inline style CSSOM access on the element.
  this._surrogateElement = createDummyElement();
  this._style = element.style;
  this._length = 0;
  this._isAnimatedProperty = {};

  // Populate the surrogate element's inline style.
  copyInlineStyle(this._style, this._surrogateElement.style);
  this._updateIndices();
};

AnimatedCSSStyleDeclaration.prototype = {
  get cssText() {
    return this._surrogateElement.style.cssText;
  },
  set cssText(text) {
    var isAffectedProperty = {};
    for (var i = 0; i < this._surrogateElement.style.length; i++) {
      isAffectedProperty[this._surrogateElement.style[i]] = true;
    }
    this._surrogateElement.style.cssText = text;
    this._updateIndices();
    for (var i = 0; i < this._surrogateElement.style.length; i++) {
      isAffectedProperty[this._surrogateElement.style[i]] = true;
    }
    for (var property in isAffectedProperty) {
      if (!this._isAnimatedProperty[property]) {
        this._style.setProperty(property,
            this._surrogateElement.style.getPropertyValue(property));
      }
    }
    animatedInlineStyleChanged();
  },
  get length() {
    return this._surrogateElement.style.length;
  },
  get parentRule() {
    return this._style.parentRule;
  },
  get 'var'() {
    return this._style.var;
  },
  _updateIndices: function() {
    while (this._length < this._surrogateElement.style.length) {
      Object.defineProperty(this, this._length, {
        configurable: true,
        enumerable: false,
        get: (function(index) {
          return function() {
            return this._surrogateElement.style[index];
          };
        })(this._length)
      });
      this._length++;
    }
    while (this._length > this._surrogateElement.style.length) {
      this._length--;
      Object.defineProperty(this, this._length, {
        configurable: true,
        enumerable: false,
        value: undefined
      });
    }
  },
  _clearAnimatedProperty: function(property) {
    this._style[property] = this._surrogateElement.style[property];
    this._isAnimatedProperty[property] = false;
  },
  _setAnimatedProperty: function(property, value) {
    this._style[property] = value;
    this._isAnimatedProperty[property] = true;
  }
};

for (var method in cssStyleDeclarationMethodModifiesStyle) {
  AnimatedCSSStyleDeclaration.prototype[method] =
      (function(method, modifiesStyle) {
    return function() {
      var result = this._surrogateElement.style[method].apply(
          this._surrogateElement.style, arguments);
      if (modifiesStyle) {
        if (!this._isAnimatedProperty[arguments[0]]) {
          this._style[method].apply(this._style, arguments);
        }
        this._updateIndices();
        animatedInlineStyleChanged();
      }
      return result;
    }
  })(method, cssStyleDeclarationMethodModifiesStyle[method]);
}

for (var property in document.documentElement.style) {
  if (cssStyleDeclarationAttribute[property] ||
      property in cssStyleDeclarationMethodModifiesStyle) {
    continue;
  }
  (function(property) {
    Object.defineProperty(AnimatedCSSStyleDeclaration.prototype, property,
        configureDescriptor({
          get: function() {
            return this._surrogateElement.style[property];
          },
          set: function(value) {
            this._surrogateElement.style[property] = value;
            this._updateIndices();
            if (!this._isAnimatedProperty[property]) {
              this._style[property] = value;
            }
            animatedInlineStyleChanged();
          }
        }));
  })(property);
}

// This function is a fallback for when we can't replace an element's style with
// AnimatatedCSSStyleDeclaration and must patch the existing style to behave
// in a similar way.
// Only the methods listed in cssStyleDeclarationMethodModifiesStyle will
// be patched to behave in the same manner as a native implementation,
// getter properties like style.left or style[0] will be tainted by the
// polyfill's animation engine.
var patchInlineStyleForAnimation = function(style) {
  var surrogateElement = document.createElement('div');
  copyInlineStyle(style, surrogateElement.style);
  var isAnimatedProperty = {};
  for (var method in cssStyleDeclarationMethodModifiesStyle) {
    if (!(method in style)) {
      continue;
    }
    Object.defineProperty(style, method, configureDescriptor({
      value: (function(method, originalMethod, modifiesStyle) {
        return function() {
          var result = surrogateElement.style[method].apply(
              surrogateElement.style, arguments);
          if (modifiesStyle) {
            if (!isAnimatedProperty[arguments[0]]) {
              originalMethod.apply(style, arguments);
            }
            animatedInlineStyleChanged();
          }
          return result;
        }
      })(method, style[method], cssStyleDeclarationMethodModifiesStyle[method])
    }));
  }

  style._clearAnimatedProperty = function(property) {
    this[property] = surrogateElement.style[property];
    isAnimatedProperty[property] = false;
  };

  style._setAnimatedProperty = function(property, value) {
    this[property] = value;
    isAnimatedProperty[property] = true;
  };
};



/** @constructor */
var Compositor = function() {
  this.targets = [];
};

Compositor.prototype = {
  setAnimatedValue: function(target, property, animValue) {
    if (target !== null) {
      if (target._animProperties === undefined) {
        target._animProperties = new CompositedPropertyMap(target);
        this.targets.push(target);
      }
      target._animProperties.addValue(property, animValue);
    }
  },
  applyAnimatedValues: function() {
    for (var i = 0; i < this.targets.length; i++) {
      this.targets[i]._animProperties.clear();
    }
    for (var i = 0; i < this.targets.length; i++) {
      this.targets[i]._animProperties.captureBaseValues();
    }
    for (var i = 0; i < this.targets.length; i++) {
      this.targets[i]._animProperties.applyAnimatedValues();
    }
  }
};

var ensureTargetInitialised = function(property, target) {
  if (propertyIsSVGAttrib(property, target)) {
    ensureTargetSVGInitialised(property, target);
  } else {
    ensureTargetCSSInitialised(target);
  }
};

var ensureTargetSVGInitialised = function(property, target) {
  if (!isDefinedAndNotNull(target._actuals)) {
    target._actuals = {};
    target._bases = {};
    target.actuals = {};
    target._getAttribute = target.getAttribute;
    target._setAttribute = target.setAttribute;
    target.getAttribute = function(name) {
      if (isDefinedAndNotNull(target._bases[name])) {
        return target._bases[name];
      }
      return target._getAttribute(name);
    };
    target.setAttribute = function(name, value) {
      if (isDefinedAndNotNull(target._actuals[name])) {
        target._bases[name] = value;
      } else {
        target._setAttribute(name, value);
      }
    };
  }
  if (!isDefinedAndNotNull(target._actuals[property])) {
    var baseVal = target.getAttribute(property);
    target._actuals[property] = 0;
    target._bases[property] = baseVal;

    Object.defineProperty(target.actuals, property, configureDescriptor({
      set: function(value) {
        if (value === null) {
          value = target._bases[property];
          if (value === null && property === 'transform') {
            // Avoid SVG error:
            // Invalid value for <element> attribute transform="null"
            value = '';
          }
        }

        target._actuals[property] = value;
        target._setAttribute(property, value);
      },
      get: function() {
        return target._actuals[property];
      }
    }));
  }
};

var ensureTargetCSSInitialised = function(target) {
  if (target.style._webAnimationsStyleInitialised) {
    return;
  }
  try {
    var animatedStyle = new AnimatedCSSStyleDeclaration(target);
    Object.defineProperty(target, 'style', configureDescriptor({
      get: function() { return animatedStyle; }
    }));
  } catch (error) {
    patchInlineStyleForAnimation(target.style);
  }
  target.style._webAnimationsStyleInitialised = true;
};

var setValue = function(target, property, value) {
  ensureTargetInitialised(property, target);
  property = prefixProperty(property);
  if (propertyIsSVGAttrib(property, target)) {
    target.actuals[property] = value;
  } else {
    target.style._setAnimatedProperty(property, value);
  }
};

var clearValue = function(target, property) {
  ensureTargetInitialised(property, target);
  property = prefixProperty(property);
  if (propertyIsSVGAttrib(property, target)) {
    target.actuals[property] = null;
  } else {
    target.style._clearAnimatedProperty(property);
  }
};

var getValue = function(target, property) {
  ensureTargetInitialised(property, target);
  property = prefixProperty(property);
  if (propertyIsSVGAttrib(property, target)) {
    return target.actuals[property];
  } else {
    return getComputedStyle(target)[property];
  }
};

var rafScheduled = false;

var compositor = new Compositor();

var usePerformanceTiming =
    typeof window.performance === 'object' &&
    typeof window.performance.timing === 'object' &&
    typeof window.performance.now === 'function';

// Don't use a local named requestAnimationFrame, to avoid potential problems
// with hoisting.
var nativeRaf = window.requestAnimationFrame ||
    window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame;
var raf;
if (nativeRaf) {
  raf = function(callback) {
    nativeRaf(function() {
      callback(clockMillis());
    });
  };
} else {
  raf = function(callback) {
    setTimeout(function() {
      callback(clockMillis());
    }, 1000 / 60);
  };
}

var clockMillis = function() {
  return usePerformanceTiming ? window.performance.now() : Date.now();
};
// Set up the zero times for document time. Document time is relative to the
// document load event.
var documentTimeZeroAsRafTime;
var documentTimeZeroAsClockTime;
var load;
if (usePerformanceTiming) {
  load = function() {
    // RAF time is relative to the navigationStart event.
    documentTimeZeroAsRafTime =
        window.performance.timing.loadEventStart -
        window.performance.timing.navigationStart;
    // performance.now() uses the same origin as RAF time.
    documentTimeZeroAsClockTime = documentTimeZeroAsRafTime;
  };
} else {
  // The best approximation we have for the relevant clock and RAF times is to
  // listen to the load event.
  load = function() {
    raf(function(rafTime) {
      documentTimeZeroAsRafTime = rafTime;
    });
    documentTimeZeroAsClockTime = Date.now();
  };
}
// Start timing when load event fires or if this script is processed when
// document loading is already complete.
if (document.readyState === 'complete') {
  // When performance timing is unavailable and this script is loaded
  // dynamically, document zero time is incorrect.
  // Warn the user in this case.
  if (!usePerformanceTiming) {
    console.warn(
        'Web animations can\'t discover document zero time when ' +
        'asynchronously loaded in the absence of performance timing.');
  }
  load();
} else {
  addEventListener('load', function() {
    load();
    if (usePerformanceTiming) {
      // We use setTimeout() to clear cachedClockTimeMillis at the end of a
      // frame, but this will not run until after other load handlers. We need
      // those handlers to pick up the new value of clockMillis(), so we must
      // clear the cached value.
      cachedClockTimeMillis = undefined;
    }
  });
}

// A cached document time for use during the current callstack.
var cachedClockTimeMillis;
// Calculates one time relative to another, returning null if the zero time is
// undefined.
var relativeTime = function(time, zeroTime) {
  return isDefined(zeroTime) ? time - zeroTime : null;
};

var lastClockTimeMillis;

var cachedClockTime = function() {
  // Cache a document time for the remainder of this callstack.
  if (!isDefined(cachedClockTimeMillis)) {
    cachedClockTimeMillis = clockMillis();
    lastClockTimeMillis = cachedClockTimeMillis;
    setTimeout(function() { cachedClockTimeMillis = undefined; }, 0);
  }
  return cachedClockTimeMillis;
};


// These functions should be called in every stack that could possibly modify
// the effect results that have already been calculated for the current tick.
var modifyCurrentAnimationStateDepth = 0;
var enterModifyCurrentAnimationState = function() {
  modifyCurrentAnimationStateDepth++;
};
var exitModifyCurrentAnimationState = function(updateCallback) {
  modifyCurrentAnimationStateDepth--;
  // updateCallback is set to null when we know we can't possibly affect the
  // current state (eg. a TimedItem which is not attached to a player). We track
  // the depth of recursive calls trigger just one repeat per entry. Only the
  // updateCallback from the outermost call is considered, this allows certain
  // locatations (eg. constructors) to override nested calls that would
  // otherwise set updateCallback unconditionally.
  if (modifyCurrentAnimationStateDepth === 0 && updateCallback) {
    updateCallback();
  }
};

var repeatLastTick = function() {
  if (isDefined(lastTickTime)) {
    ticker(lastTickTime, true);
  }
};

var playerSortFunction = function(a, b) {
  var result = a.startTime - b.startTime;
  return result !== 0 ? result : a._sequenceNumber - b._sequenceNumber;
};

var lastTickTime;
var ticker = function(rafTime, isRepeat) {
  // Don't tick till the page is loaded....
  if (!isDefined(documentTimeZeroAsRafTime)) {
    raf(ticker);
    return;
  }

  if (!isRepeat) {
    if (rafTime < lastClockTimeMillis) {
      rafTime = lastClockTimeMillis;
    }
    lastTickTime = rafTime;
    cachedClockTimeMillis = rafTime;
  }

  // Clear any modifications to getComputedStyle.
  ensureOriginalGetComputedStyle();

  // Get animations for this sample. We order by AnimationPlayer then by DFS
  // order within each AnimationPlayer's tree.
  if (!playersAreSorted) {
    PLAYERS.sort(playerSortFunction);
    playersAreSorted = true;
  }
  var finished = true;
  var paused = true;
  var animations = [];
  var finishedPlayers = [];
  PLAYERS.forEach(function(player) {
    player._update();
    finished = finished && !player._hasFutureAnimation();
    if (!player._hasFutureEffect()) {
      finishedPlayers.push(player);
    }
    paused = paused && player.paused;
    player._getLeafItemsInEffect(animations);
  });

  // Apply animations in order
  for (var i = 0; i < animations.length; i++) {
    if (animations[i] instanceof Animation) {
      animations[i]._sample();
    }
  }

  // Generate events
  PLAYERS.forEach(function(player) {
    player._generateEvents();
  });

  // Remove finished players. Warning: _deregisterFromTimeline modifies
  // the PLAYER list. It should not be called from within a PLAYERS.forEach
  // loop directly.
  finishedPlayers.forEach(function(player) {
    player._deregisterFromTimeline();
    playersAreSorted = false;
  });

  // Composite animated values into element styles
  compositor.applyAnimatedValues();

  if (!isRepeat) {
    if (finished || paused) {
      rafScheduled = false;
    } else {
      raf(ticker);
    }
    cachedClockTimeMillis = undefined;
  }
};

// Multiplication where zero multiplied by any value (including infinity)
// gives zero.
var multiplyZeroGivesZero = function(a, b) {
  return (a === 0 || b === 0) ? 0 : a * b;
};

var maybeRestartAnimation = function() {
  if (rafScheduled) {
    return;
  }
  raf(ticker);
  rafScheduled = true;
};

var DOCUMENT_TIMELINE = new AnimationTimeline(constructorToken);
// attempt to override native implementation
try {
  Object.defineProperty(document, 'timeline', {
    configurable: true,
    get: function() { return DOCUMENT_TIMELINE }
  });
} catch (e) { }
// maintain support for Safari
try {
  document.timeline = DOCUMENT_TIMELINE;
} catch (e) { }

window.Element.prototype.animate = function(effect, timing) {
  var anim = new Animation(this, effect, timing);
  DOCUMENT_TIMELINE.play(anim);
  return anim.player;
};
window.Element.prototype.getCurrentPlayers = function() {
  return PLAYERS.filter((function(player) {
    return player._isCurrent() && player._isTargetingElement(this);
  }).bind(this));
};
window.Element.prototype.getCurrentAnimations = function() {
  var animations = [];
  PLAYERS.forEach((function(player) {
    if (player._isCurrent()) {
      player._getAnimationsTargetingElement(this, animations);
    }
  }).bind(this));
  return animations;
};

window.Animation = Animation;
window.AnimationEffect = AnimationEffect;
window.AnimationGroup = AnimationGroup;
window.AnimationPlayer = AnimationPlayer;
window.AnimationSequence = AnimationSequence;
window.AnimationTimeline = AnimationTimeline;
window.KeyframeEffect = KeyframeEffect;
window.MediaReference = MediaReference;
window.MotionPathEffect = MotionPathEffect;
window.PseudoElementReference = PseudoElementReference;
window.TimedItem = TimedItem;
window.TimedItemList = TimedItemList;
window.Timing = Timing;
window.TimingEvent = TimingEvent;
window.TimingGroup = TimingGroup;

window._WebAnimationsTestingUtilities = {
  _constructorToken: constructorToken,
  _deprecated: deprecated,
  _positionListType: positionListType,
  _hsl2rgb: hsl2rgb,
  _types: propertyTypes,
  _knownPlayers: PLAYERS,
  _prefixProperty: prefixProperty,
  _propertyIsSVGAttrib: propertyIsSVGAttrib
};

})();