index.js

exports.compare = function (a, b) {

  if(Buffer.isBuffer(a)) {
    var l = Math.min(a.length, b.length)
    for(var i = 0; i < l; i++) {
      var cmp = a[i] - b[i]
      if(cmp) return cmp
    }
    return a.length - b.length
  }

  return a < b ? -1 : a > b ? 1 : 0
}

// to be compatible with the current abstract-leveldown tests
// nullish or empty strings.
// I could use !!val but I want to permit numbers and booleans,
// if possible.

function isDef (val) {
  return val !== undefined && val !== ''
}

function has (range, name) {
  return Object.hasOwnProperty.call(range, name)
}

function hasKey(range, name) {
  return Object.hasOwnProperty.call(range, name) && name
}

var lowerBoundKey = exports.lowerBoundKey = function (range) {
    return (
       hasKey(range, 'gt')
    || hasKey(range, 'gte')
    || hasKey(range, 'min')
    || (range.reverse ? hasKey(range, 'end') : hasKey(range, 'start'))
    || undefined
    )
}

var lowerBound = exports.lowerBound = function (range, def) {
  var k = lowerBoundKey(range)
  return k ? range[k] : def
}

var lowerBoundInclusive = exports.lowerBoundInclusive = function (range) {
  return has(range, 'gt') ? false : true
}

var upperBoundInclusive = exports.upperBoundInclusive =
  function (range) {
    return (has(range, 'lt') /*&& !range.maxEx*/) ? false : true
  }

var lowerBoundExclusive = exports.lowerBoundExclusive =
  function (range) {
    return !lowerBoundInclusive(range)
  }

var upperBoundExclusive = exports.upperBoundExclusive =
  function (range) {
    return !upperBoundInclusive(range)
  }

var upperBoundKey = exports.upperBoundKey = function (range) {
    return (
       hasKey(range, 'lt')
    || hasKey(range, 'lte')
    || hasKey(range, 'max')
    || (range.reverse ? hasKey(range, 'start') : hasKey(range, 'end'))
    || undefined
    )
}

var upperBound = exports.upperBound = function (range, def) {
  var k = upperBoundKey(range)
  return k ? range[k] : def
}

exports.start = function (range, def) {
  return range.reverse ? upperBound(range, def) : lowerBound(range, def)
}
exports.end = function (range, def) {
  return range.reverse ? lowerBound(range, def) : upperBound(range, def)
}
exports.startInclusive = function (range) {
  return (
    range.reverse
  ? upperBoundInclusive(range)
  : lowerBoundInclusive(range)
  )
}
exports.endInclusive = function (range) {
  return (
    range.reverse
  ? lowerBoundInclusive(range)
  : upperBoundInclusive(range)
  )
}

function id (e) { return e }

exports.toLtgt = function (range, _range, map, lower, upper) {
  _range = _range || {}
  map = map || id
  var defaults = arguments.length > 3
  var lb = exports.lowerBoundKey(range)
  var ub = exports.upperBoundKey(range)
  if(lb) {
    if(lb === 'gt') _range.gt = map(range.gt, false)
    else            _range.gte = map(range[lb], false)
  }
  else if(defaults)
    _range.gte = map(lower, false)

  if(ub) {
    if(ub === 'lt') _range.lt = map(range.lt, true)
    else            _range.lte = map(range[ub], true)
  }
  else if(defaults)
    _range.lte = map(upper, true)

  if(range.reverse != null)
    _range.reverse = !!range.reverse

  //if range was used mutably
  //(in level-sublevel it's part of an options object
  //that has more properties on it.)
  if(has(_range, 'max'))   delete _range.max
  if(has(_range, 'min'))   delete _range.min
  if(has(_range, 'start')) delete _range.start
  if(has(_range, 'end'))   delete _range.end

  return _range
}

exports.contains = function (range, key, compare) {
  compare = compare || exports.compare

  var lb = lowerBound(range)
  if(isDef(lb)) {
    var cmp = compare(key, lb)
    if(cmp < 0 || (cmp === 0 && lowerBoundExclusive(range)))
      return false
  }

  var ub = upperBound(range)
  if(isDef(ub)) {
    var cmp = compare(key, ub)
    if(cmp > 0 || (cmp === 0) && upperBoundExclusive(range))
      return false
  }

  return true
}

exports.filter = function (range, compare) {
  return function (key) {
    return exports.contains(range, key, compare)
  }
}