/*
    Ember Data has 3 buckets for storing the value of an attribute on an internalModel.

    `_data` holds all of the attributes that have been acknowledged by
    a backend via the adapter. When rollbackAttributes is called on a model all
    attributes will revert to the record's state in `_data`.

    `_attributes` holds any change the user has made to an attribute
    that has not been acknowledged by the adapter. Any values in
    `_attributes` are have priority over values in `_data`.

    `_inFlightAttributes`. When a record is being synced with the
    backend the values in `_attributes` are copied to
    `_inFlightAttributes`. This way if the backend acknowledges the
    save but does not return the new state Ember Data can copy the
    values from `_inFlightAttributes` to `_data`. Without having to
    worry about changes made to `_attributes` while the save was
    happenign.


    Changed keys builds a list of all of the values that may have been
    changed by the backend after a successful save.

    It does this by iterating over each key, value pair in the payload
    returned from the server after a save. If the `key` is found in
    `_attributes` then the user has a local changed to the attribute
    that has not been synced with the server and the key is not
    included in the list of changed keys.



    If the value, for a key differs from the value in what Ember Data
    believes to be the truth about the backend state (A merger of the
    `_data` and `_inFlightAttributes` objects where
    `_inFlightAttributes` has priority) then that means the backend
    has updated the value and the key is added to the list of changed
    keys.

    @method _changedKeys
    @private
  */
  /*
      TODO IGOR DAVID
      There seems to be a potential bug here, where we will return keys that are not
      in the schema
  */
  _changedKeys(updates) {
    let changedKeys: string[] = [];

    if (updates) {
      let original, i, value, key;
      let keys = Object.keys(updates);
      let length = keys.length;
      let hasAttrs = this.hasChangedAttributes();
      let attrs;
      if (hasAttrs) {
        attrs = this._attributes;
      }

      original = assign(Object.create(null), this._data, this.__inFlightAttributes);

      for (i = 0; i < length; i++) {
        key = keys[i];
        value = updates[key];

        // A value in _attributes means the user has a local change to
        // this attributes. We never override this value when merging
        // updates from the backend so we should not sent a change
        // notification if the server value differs from the original.
        if (hasAttrs === true && attrs[key] !== undefined) {
          continue;
        }

        if (!isEqual(original[key], value)) {
          changedKeys.push(key);
        }
      }
    }

    return changedKeys;
  }

(function() {
    /** isEqual */
    isEqual('foo', 'bar'); // $ExpectType boolean
    isEqual(14, 37); // $ExpectType boolean
    isEqual(14, '1'); // $ExpectType boolean
    isEqual(() => 4, () => 37); // $ExpectType boolean
    isEqual(14); // $ExpectError
    isEqual(); // $ExpectError
})();