app-pouchdb-conflict-resolution.html

<!--
@license
Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
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The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->
<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="pouchdb.html">
<!--
`app-pouchdb-conflict-resolution` enables declarative configuration of conflict
resolution strategies ordered by logical relationships in the DOM. Currently
two basic strategies are supported: `firstWriteWins` and `lastWriteWins`.

To use `app-pouchdb-conflict-resolution`, simply include the element somewhere
in a document subtree at or above the ShadowRoot of an `app-pouchdb-document`
or `app-pouchdb-query`:

```html
<app-pouchdb-conflict-resolution
    strategy="lastWriteWins">
</app-pouchdb-conflict-resolution>
<app-pouchdb-document
    db-name="cats"
    doc-id="parsnip">
</app-pouchdb-document>
```

When a conflict occurs, the `app-pouchdb-document` will request fire an event
to notify of the conflict and request a resolution strategy. The
`app-pouchdb-conflict-resolution` element listens at its nearest ShadowRoot
boundary for conflict notifications, and responds to them as needed with a
configured strategy.
-->
<script>
  (function() {
  'use strict';

  Polymer({
    is: 'app-pouchdb-conflict-resolution',

    properties: {
      /**
       * The name of the strategy to use to reslve the conflict. Supported
       * strategies are `firstWriteWins` (the default) and `lastWriteWins`.
       */
      strategy: {type: String, value: 'firstWriteWins'},

      /**
       * By default, this element stops propagation of any conflict events
       * that it is able to handle. If set to `true`, the element will allow
       * such events to continue propagating, opening the possibility that
       * another conflict resolution strategy higher up the document tree will
       * superseed this one.
       */
      allowAncestralResolution: {type: Boolean, value: false}
    },

    created: function() {
      this._eventTarget = null;
    },

    attached: function() {
      this._eventTarget = Polymer.dom(this).host || document;
      this.listen(this._eventTarget, 'app-pouchdb-conflict', 'resolveConflict');
    },

    detached: function() {
      this.unlisten(this._eventTarget, 'app-pouchdb-conflict', 'resolveConflict');
    },

    resolveConflict: function(event) {
      if (!this.strategy || !this[this.strategy]) {
        return Promise.reject('No resolution strategy available.');
      }

      event.detail.resolveConflict(this[this.strategy].bind(this));

      if (!this.allowAncestralResolution) {
        event.stopImmediatePropagation();
      }
    },

    firstWriteWins: function(db, method, doc, error) {
      return db.get(doc._id).then(function(canonicalDoc) {
        return {id: canonicalDoc._id, rev: canonicalDoc._rev};
      });
      return Promise.resolve();
    },

    lastWriteWins: function(db, method, doc, error) {
      return db.get(doc._id, {conflicts: true}).then(function(canonicalDoc) {
        doc._rev = canonicalDoc._rev;
        return db.put(doc);
      }.bind(this));
    }
  });
  })();
</script>