define(function(require) {
  'use strict';
  var Ember = require('ember');

  return Ember.Mixin.create({
    /**
     * Cache all relationship IDs each time the model is loaded or updated.
     * This data is required to determine if any relationships contain new
     * records (or omit old records) since the last server synchronization
     * (see this mixin's `areRelationshipsDirty` and `rollbackRelationships`
     * methods).
     */
    _handleSync: function() {
      var members = {};

      this.eachRelationship(function(name) {
        members[name] = this.get('data.' + name).mapBy('id');
      }, this);

      this.set('_cleanRelationshipMembers', members);
    }.on('didLoad', 'didUpdate'),

    /**
     * Determine if any of the model's relationships have changed members since
     * the last synchronization with the server.
     *
     * @return {Boolean}
     */
    areRelationshipsDirty: function() {
      var previous = this.get('_cleanRelationshipMembers');

      if (!previous) {
        return false;
      }

      return !Ember.keys(previous).every(function(name) {
        var currentIds = this.get('data.' + name).mapBy('id');
        var previousIds = previous[name];

        if (currentIds.length !== previousIds.length) {
          return false;
        }

        return previousIds.every(function(id) {
          return currentIds.indexOf(id) > -1;
        });
      }, this);
    },

    /**
     * Revert any and all relationships to their last-known synchronized state.
     */
    rollbackRelationships: function() {
      var store = this.store;
      var cleanRelationshipMembers = this.get('_cleanRelationshipMembers');

      /**
       * As a minor performance optimization, do not re-set any relationships
       * if none of them are dirty.
       */
      if (!this.areRelationshipsDirty()) {
        return;
      }

      this.eachRelationship(function(name, descriptor) {
        var typeKey = descriptor.type.typeKey;
        var cleanMemberIds = cleanRelationshipMembers[name];

        var cleanMembers = cleanMemberIds.map(function(id) {
          return store.getById(typeKey, id);
        });

        this.set('data.' + name, cleanMembers);
      }, this);
    },

    /**
     * Extend `Model#rollback` to provide ensure that the members of all
     * relationships are reverted
     */
    rollback: function() {
      this.rollbackRelationships();

      this._super.apply(this, arguments);
    }

  });
});