text: const _ = require('underscore');
  const AVError = require('./error');
  const {
    _request,
   } = require('./request');
  const {
    isNullOrUndefined,
    ensureArray,
    transformFetchOptions,
    setValue,
    findValue,
  } = require('./utils');
  
  const RESERVED_KEYS = ['objectId', 'createdAt', 'updatedAt'];
  const checkReservedKey = key => {
    if (RESERVED_KEYS.indexOf(key) !== -1) {
      throw new Error(`key[${key}] is reserved`);
    }
  };
  
  const handleBatchResults = (results) => {
    const firstError = _.find(results, result => result instanceof Error);
    if (!firstError) {
      return results;
    }
    const error = new AVError(firstError.code, firstError.message);
    error.results = results;
    throw error;
  };
  
  // Helper function to get a value from a Backbone object as a property
  // or as a function.
  function getValue(object, prop) {
    if (!(object && object[prop])) {
      return null;
    }
    return _.isFunction(object[prop]) ? object[prop]() : object[prop];
  }
  
  // AV.Object is analogous to the Java AVObject.
  // It also implements the same interface as a Backbone model.
  
  module.exports = function(AV) {
    /**
     * Creates a new model with defined attributes. A client id (cid) is
     * automatically generated and assigned for you.
     *
     * <p>You won't normally call this method directly.  It is recommended that
     * you use a subclass of <code>AV.Object</code> instead, created by calling
     * <code>extend</code>.</p>
     *
     * <p>However, if you don't want to use a subclass, or aren't sure which
     * subclass is appropriate, you can use this form:<pre>
     *     var object = new AV.Object("ClassName");
     * </pre>
     * That is basically equivalent to:<pre>
     *     var MyClass = AV.Object.extend("ClassName");
     *     var object = new MyClass();
     * </pre></p>
     *
     * @param {Object} attributes The initial set of data to store in the object.
     * @param {Object} options A set of Backbone-like options for creating the
     *     object.  The only option currently supported is "collection".
     * @see AV.Object.extend
     *
     * @class
     *
     * <p>The fundamental unit of AV data, which implements the Backbone Model
     * interface.</p>
     */
    AV.Object = function(attributes, options) {
      // Allow new AV.Object("ClassName") as a shortcut to _create.
      if (_.isString(attributes)) {
        return AV.Object._create.apply(this, arguments);
      }
  
      attributes = attributes || {};
      if (options && options.parse) {
        attributes = this.parse(attributes);
        attributes = this._mergeMagicFields(attributes);
      }
      var defaults = getValue(this, 'defaults');
      if (defaults) {
        attributes = _.extend({}, defaults, attributes);
      }
      if (options && options.collection) {
        this.collection = options.collection;
      }
  
      this._serverData = {};  // The last known data for this object from cloud.
      this._opSetQueue = [{}];  // List of sets of changes to the data.
      this._flags = {};
      this.attributes = {};  // The best estimate of this's current data.
  
      this._hashedJSON = {};  // Hash of values of containers at last save.
      this._escapedAttributes = {};
      this.cid = _.uniqueId('c');
      this.changed = {};
      this._silent = {};
      this._pending = {};
      this.set(attributes, { silent: true });
      this.changed = {};
      this._silent = {};
      this._pending = {};
      this._hasData = true;
      this._previousAttributes = _.clone(this.attributes);
      this.initialize.apply(this, arguments);
    };
  
    /**
     * @lends AV.Object.prototype
     * @property {String} id The objectId of the AV Object.
     */
  
    /**
     * Saves the given list of AV.Object.
     * If any error is encountered, stops and calls the error handler.
     *
     * @example
     * AV.Object.saveAll([object1, object2, ...]).then(function(list) {
     *   // All the objects were saved.
     * }, function(error) {
     *   // An error occurred while saving one of the objects.
     * });
     *
     * @param {Array} list A list of <code>AV.Object</code>.
     */
    AV.Object.saveAll = function(list, options) {
      return AV.Object._deepSaveAsync(list, null, options);
    };
  
    /**
     * Fetch the given list of AV.Object.
     *
     * @param {AV.Object[]} objects A list of <code>AV.Object</code>
     * @param {AuthOptions} options
     * @return {Promise.<AV.Object[]>} The given list of <code>AV.Object</code>, updated
     */
  
    AV.Object.fetchAll = (objects, options) =>
      AV.Promise.resolve().then(() =>
        _request('batch', null, null, 'POST', {
          requests: _.map(objects, object => {
            if (!object.className) throw new Error('object must have className to fetch');
            if (!object.id) throw new Error('object must have id to fetch');
            if (object.dirty()) throw new Error('object is modified but not saved');
            return {
              method: 'GET',
              path: `/1.1/classes/${object.className}/${object.id}`,
            };
          }),
        }, options)
      ).then(function(response) {
        const results = _.map(objects, function(object, i) {
          if (response[i].success) {
            object._finishFetch(object.parse(response[i].success));
            return object;
          }
          if (response[i].success === null) {
            return new AVError(AVError.OBJECT_NOT_FOUND, 'Object not found.');
          }
          return new AVError(response[i].error.code, response[i].error.error);
        });
        return handleBatchResults(results);
      });
  
    // Attach all inheritable methods to the AV.Object prototype.
    _.extend(AV.Object.prototype, AV.Events,
             /** @lends AV.Object.prototype */ {
      _fetchWhenSave: false,
  
      /**
       * Initialize is an empty function by default. Override it with your own
       * initialization logic.
       */
      initialize: function(){},
  
     /**
       * Set whether to enable fetchWhenSave option when updating object.
       * When set true, SDK would fetch the latest object after saving.
       * Default is false.
       *
       * @deprecated use AV.Object#save with options.fetchWhenSave instead
       * @param {boolean} enable  true to enable fetchWhenSave option.
       */
      fetchWhenSave: function(enable){
        console.warn('AV.Object#fetchWhenSave is deprecated, use AV.Object#save with options.fetchWhenSave instead.');
        if (!_.isBoolean(enable)) {
          throw new Error('Expect boolean value for fetchWhenSave');
        }
        this._fetchWhenSave = enable;
      },
  
     /**
      * Returns the object's objectId.
      * @return {String} the objectId.
      */
      getObjectId: function() {
        return this.id;
      },
  
     /**
      * Returns the object's createdAt attribute.
      * @return {Date}
      */
      getCreatedAt: function() {
        return this.createdAt || this.get('createdAt');
      },
  
     /**
      * Returns the object's updatedAt attribute.
      * @return {Date}
      */
      getUpdatedAt: function() {
        return this.updatedAt || this.get('updatedAt');
      },
  
      /**
       * Returns a JSON version of the object.
       * @return {Object}
       */
      toJSON: function(key, holder, seenObjects = []) {
        return this._toFullJSON(seenObjects, false);
      },
  
      /**
       * Returns a JSON version of the object with meta data.
       * Inverse to {@link AV.parseJSON}
       * @since 2.0.0
       * @return {Object}
       */
      toFullJSON(seenObjects = []) {
        return this._toFullJSON(seenObjects);
      },
  
      _toFullJSON: function(seenObjects, full = true) {
        var json = _.clone(this.attributes);
        if (_.isArray(seenObjects)) {
          var newSeenObjects = seenObjects.concat(this);
        }
        AV._objectEach(json, function(val, key) {
          json[key] = AV._encode(val, newSeenObjects, undefined, full);
        });
        AV._objectEach(this._operations, function(val, key) {
          json[key] = val;
        });
  
        if (_.has(this, "id")) {
          json.objectId = this.id;
        }
        _(['createdAt', 'updatedAt']).each((key) => {
          if (_.has(this, key)) {
            const val = this[key];
            json[key] = _.isDate(val) ? val.toJSON() : val;
          }
        });
        if (full) {
          json.__type = "Object";
          if (_.isArray(seenObjects) && seenObjects.length) json.__type = "Pointer";
          json.className = this.className;
        }
        return json;
      },
  
      /**
       * Updates _hashedJSON to reflect the current state of this object.
       * Adds any changed hash values to the set of pending changes.
       * @private
       */
      _refreshCache: function() {
        var self = this;
        if (self._refreshingCache) {
          return;
        }
        self._refreshingCache = true;
        AV._objectEach(this.attributes, function(value, key) {
          if (value instanceof AV.Object) {
            value._refreshCache();
          } else if (_.isObject(value)) {
            if (self._resetCacheForKey(key)) {
              self.set(key, new AV.Op.Set(value), { silent: true });
            }
          }
        });
        delete self._refreshingCache;
      },
  
      /**
       * Returns true if this object has been modified since its last
       * save/refresh.  If an attribute is specified, it returns true only if that
       * particular attribute has been modified since the last save/refresh.
       * @param {String} attr An attribute name (optional).
       * @return {Boolean}
       */
      dirty: function(attr) {
        this._refreshCache();
  
        return this._dirty();
      },
  
      _dirty: function(attr) {
        var currentChanges = _.last(this._opSetQueue);
  
        if (attr) {
          return (currentChanges[attr] ? true : false);
        }
        if (!this.id) {
          return true;
        }
        if (_.keys(currentChanges).length > 0) {
          return true;
        }
        return false;
      },
  
      /**
       * Gets a Pointer referencing this Object.
       * @private
       */
      _toPointer: function() {
        // if (!this.id) {
        //   throw new Error("Can't serialize an unsaved AV.Object");
        // }
        return { __type: "Pointer",
                 className: this.className,
                 objectId: this.id };
      },
  
      /**
       * Gets the value of an attribute.
       * @param {String} attr The string name of an attribute.
       */
      get: function(attr) {
        switch (attr) {
          case 'objectId':
            return this.id;
          case 'createdAt':
          case 'updatedAt':
            return this[attr];
          default:
            return this.attributes[attr];
        }
      },
  
      /**
       * Gets a relation on the given class for the attribute.
       * @param {String} attr The attribute to get the relation for.
       * @return {AV.Relation}
       */
      relation: function(attr) {
        var value = this.get(attr);
        if (value) {
          if (!(value instanceof AV.Relation)) {
            throw new Error("Called relation() on non-relation field " + attr);
          }
          value._ensureParentAndKey(this, attr);
          return value;
        } else {
          return new AV.Relation(this, attr);
        }
      },
  
      /**
       * Gets the HTML-escaped value of an attribute.
       */
      escape: function(attr) {
        var html = this._escapedAttributes[attr];
        if (html) {
          return html;
        }
        var val = this.attributes[attr];
        var escaped;
        if (isNullOrUndefined(val)) {
          escaped = '';
        } else {
          escaped = _.escape(val.toString());
        }
        this._escapedAttributes[attr] = escaped;
        return escaped;
      },
  
      /**
       * Returns <code>true</code> if the attribute contains a value that is not
       * null or undefined.
       * @param {String} attr The string name of the attribute.
       * @return {Boolean}
       */
      has: function(attr) {
        return !isNullOrUndefined(this.attributes[attr]);
      },
  
      /**
       * Pulls "special" fields like objectId, createdAt, etc. out of attrs
       * and puts them on "this" directly.  Removes them from attrs.
       * @param attrs - A dictionary with the data for this AV.Object.
       * @private
       */
      _mergeMagicFields: function(attrs) {
        // Check for changes of magic fields.
        var model = this;
        var specialFields = ["objectId", "createdAt", "updatedAt"];
        AV._arrayEach(specialFields, function(attr) {
          if (attrs[attr]) {
            if (attr === "objectId") {
              model.id = attrs[attr];
            } else if ((attr === "createdAt" || attr === "updatedAt") &&
                       !_.isDate(attrs[attr])) {
              model[attr] = AV._parseDate(attrs[attr]);
            } else { 
              model[attr] = attrs[attr]; 
            }
            delete attrs[attr];
          }
        });
        return attrs;
      },
  
      /**
       * Returns the json to be sent to the server.
       * @private
       */
      _startSave: function() {
        this._opSetQueue.push({});
      },
  
      /**
       * Called when a save fails because of an error. Any changes that were part
       * of the save need to be merged with changes made after the save. This
       * might throw an exception is you do conflicting operations. For example,
       * if you do:
       *   object.set("foo", "bar");
       *   object.set("invalid field name", "baz");
       *   object.save();
       *   object.increment("foo");
       * then this will throw when the save fails and the client tries to merge
       * "bar" with the +1.
       * @private
       */
      _cancelSave: function() {
        var self = this;
        var failedChanges = _.first(this._opSetQueue);
        this._opSetQueue = _.rest(this._opSetQueue);
        var nextChanges = _.first(this._opSetQueue);
        AV._objectEach(failedChanges, function(op, key) {
          var op1 = failedChanges[key];
          var op2 = nextChanges[key];
          if (op1 && op2) {
            nextChanges[key] = op2._mergeWithPrevious(op1);
          } else if (op1) {
            nextChanges[key] = op1;
          }
        });
        this._saving = this._saving - 1;
      },
  
      /**
       * Called when a save completes successfully. This merges the changes that
       * were saved into the known server data, and overrides it with any data
       * sent directly from the server.
       * @private
       */
      _finishSave: function(serverData) {
        // Grab a copy of any object referenced by this object. These instances
        // may have already been fetched, and we don't want to lose their data.
        // Note that doing it like this means we will unify separate copies of the
        // same object, but that's a risk we have to take.
        var fetchedObjects = {};
        AV._traverse(this.attributes, function(object) {
          if (object instanceof AV.Object && object.id && object._hasData) {
            fetchedObjects[object.id] = object;
          }
        });
  
        var savedChanges = _.first(this._opSetQueue);
        this._opSetQueue = _.rest(this._opSetQueue);
        this._applyOpSet(savedChanges, this._serverData);
        this._mergeMagicFields(serverData);
        var self = this;
        AV._objectEach(serverData, function(value, key) {
          self._serverData[key] = AV._decode(value, key);
  
          // Look for any objects that might have become unfetched and fix them
          // by replacing their values with the previously observed values.
          var fetched = AV._traverse(self._serverData[key], function(object) {
            if (object instanceof AV.Object && fetchedObjects[object.id]) {
              return fetchedObjects[object.id];
            }
          });
          if (fetched) {
            self._serverData[key] = fetched;
          }
        });
        this._rebuildAllEstimatedData();
        this._saving = this._saving - 1;
      },
  
      /**
       * Called when a fetch or login is complete to set the known server data to
       * the given object.
       * @private
       */
      _finishFetch: function(serverData, hasData) {
        // Clear out any changes the user might have made previously.
        this._opSetQueue = [{}];
  
        // Bring in all the new server data.
        this._mergeMagicFields(serverData);
        var self = this;
        AV._objectEach(serverData, function(value, key) {
          self._serverData[key] = AV._decode(value, key);
        });
  
        // Refresh the attributes.
        this._rebuildAllEstimatedData();
  
        // Clear out the cache of mutable containers.
        this._refreshCache();
        this._opSetQueue = [{}];
  
        this._hasData = hasData;
      },
  
      /**
       * Applies the set of AV.Op in opSet to the object target.
       * @private
       */
      _applyOpSet: function(opSet, target) {
        var self = this;
        AV._objectEach(opSet, function(change, key) {
          const [value, actualTarget, actualKey] = findValue(target, key);
          setValue(target, key, change._estimate(value, self, key));
          if (actualTarget && actualTarget[actualKey] === AV.Op._UNSET) {
            delete actualTarget[actualKey];
          }
        });
      },
  
      /**
       * Replaces the cached value for key with the current value.
       * Returns true if the new value is different than the old value.
       * @private
       */
      _resetCacheForKey: function(key) {
        var value = this.attributes[key];
        if (_.isObject(value) &&
            !(value instanceof AV.Object) &&
            !(value instanceof AV.File)) {
  
          value = value.toJSON ? value.toJSON() : value;
          var json = JSON.stringify(value);
          if (this._hashedJSON[key] !== json) {
            var wasSet = !! this._hashedJSON[key];
            this._hashedJSON[key] = json;
            return wasSet;
          }
        }
        return false;
      },
  
      /**
       * Populates attributes[key] by starting with the last known data from the
       * server, and applying all of the local changes that have been made to that
       * key since then.
       * @private
       */
      _rebuildEstimatedDataForKey: function(key) {
        var self = this;
        delete this.attributes[key];
        if (this._serverData[key]) {
          this.attributes[key] = this._serverData[key];
        }
        AV._arrayEach(this._opSetQueue, function(opSet) {
          var op = opSet[key];
          if (op) {
            const [value, actualTarget, actualKey] = findValue(self.attributes, key);
            setValue(self.attributes, key, op._estimate(value, self, key));
            if (actualTarget && actualTarget[actualKey] === AV.Op._UNSET) {
              delete actualTarget[actualKey];
            } else {
              self._resetCacheForKey(key);
            }
          }
        });
      },
  
      /**
       * Populates attributes by starting with the last known data from the
       * server, and applying all of the local changes that have been made since
       * then.
       * @private
       */
      _rebuildAllEstimatedData: function() {
        var self = this;
  
        var previousAttributes = _.clone(this.attributes);
  
        this.attributes = _.clone(this._serverData);
        AV._arrayEach(this._opSetQueue, function(opSet) {
          self._applyOpSet(opSet, self.attributes);
          AV._objectEach(opSet, function(op, key) {
            self._resetCacheForKey(key);
          });
        });
  
        // Trigger change events for anything that changed because of the fetch.
        AV._objectEach(previousAttributes, function(oldValue, key) {
          if (self.attributes[key] !== oldValue) {
            self.trigger('change:' + key, self, self.attributes[key], {});
          }
        });
        AV._objectEach(this.attributes, function(newValue, key) {
          if (!_.has(previousAttributes, key)) {
            self.trigger('change:' + key, self, newValue, {});
          }
        });
      },
  
      /**
       * Sets a hash of model attributes on the object, firing
       * <code>"change"</code> unless you choose to silence it.
       *
       * <p>You can call it with an object containing keys and values, or with one
       * key and value.  For example:</p>
       *
       * @example
       * gameTurn.set({
       *   player: player1,
       *   diceRoll: 2
       * }, {
       *   error: function(gameTurnAgain, error) {
       *     // The set failed validation.
       *   }
       * });
       *
       * game.set("currentPlayer", player2, {
       *   error: function(gameTurnAgain, error) {
       *     // The set failed validation.
       *   }
       * });
       *
       * game.set("finished", true);
       *
       * @param {String} key The key to set.
       * @param {Any} value The value to give it.
       * @param {Object} [options]
       * @param {Boolean} [options.silent]
       * @return {AV.Object} self if succeeded, throws if the value is not valid.
       * @see AV.Object#validate
       */
      set: function(key, value, options) {
        var attrs;
        if (_.isObject(key) || isNullOrUndefined(key)) {
          attrs = _.mapObject(key, function(v, k) {
            checkReservedKey(k);
            return AV._decode(v, k);
          });
          options = value;
        } else {
          attrs = {};
          checkReservedKey(key);
          attrs[key] = AV._decode(value, key);
        }
  
        // Extract attributes and options.
        options = options || {};
        if (!attrs) {
          return this;
        }
        if (attrs instanceof AV.Object) {
          attrs = attrs.attributes;
        }
  
        // If the unset option is used, every attribute should be a Unset.
        if (options.unset) {
          AV._objectEach(attrs, function(unused_value, key) {
            attrs[key] = new AV.Op.Unset();
          });
        }
  
        // Apply all the attributes to get the estimated values.
        var dataToValidate = _.clone(attrs);
        var self = this;
        AV._objectEach(dataToValidate, function(value, key) {
          if (value instanceof AV.Op) {
            dataToValidate[key] = value._estimate(self.attributes[key],
                                                  self, key);
            if (dataToValidate[key] === AV.Op._UNSET) {
              delete dataToValidate[key];
            }
          }
        });
  
        // Run validation.
        this._validate(attrs, options);
  
        options.changes = {};
        var escaped = this._escapedAttributes;
        var prev = this._previousAttributes || {};
  
        // Update attributes.
        AV._arrayEach(_.keys(attrs), function(attr) {
          var val = attrs[attr];
  
          // If this is a relation object we need to set the parent correctly,
          // since the location where it was parsed does not have access to
          // this object.
          if (val instanceof AV.Relation) {
            val.parent = self;
          }
  
          if (!(val instanceof AV.Op)) {
            val = new AV.Op.Set(val);
          }
  
          // See if this change will actually have any effect.
          var isRealChange = true;
          if (val instanceof AV.Op.Set &&
              _.isEqual(self.attributes[attr], val.value)) {
            isRealChange = false;
          }
  
          if (isRealChange) {
            delete escaped[attr];
            if (options.silent) {
              self._silent[attr] = true;
            } else {
              options.changes[attr] = true;
            }
          }
  
          var currentChanges = _.last(self._opSetQueue);
          currentChanges[attr] = val._mergeWithPrevious(currentChanges[attr]);
          self._rebuildEstimatedDataForKey(attr);
  
          if (isRealChange) {
            self.changed[attr] = self.attributes[attr];
            if (!options.silent) {
              self._pending[attr] = true;
            }
          } else {
            delete self.changed[attr];
            delete self._pending[attr];
          }
        });
  
        if (!options.silent) {
          this.change(options);
        }
        return this;
      },
  
      /**
       * Remove an attribute from the model, firing <code>"change"</code> unless
       * you choose to silence it. This is a noop if the attribute doesn't
       * exist.
       */
      unset: function(attr, options) {
        options = options || {};
        options.unset = true;
        return this.set(attr, null, options);
      },
  
      /**
       * Atomically increments the value of the given attribute the next time the
       * object is saved. If no amount is specified, 1 is used by default.
       *
       * @param attr {String} The key.
       * @param amount {Number} The amount to increment by.
       */
      increment: function(attr, amount) {
        if (_.isUndefined(amount) || _.isNull(amount)) {
          amount = 1;
        }
        return this.set(attr, new AV.Op.Increment(amount));
      },
  
      /**
       * Atomically add an object to the end of the array associated with a given
       * key.
       * @param attr {String} The key.
       * @param item {} The item to add.
       */
      add: function(attr, item) {
        return this.set(attr, new AV.Op.Add(ensureArray(item)));
      },
  
      /**
       * Atomically add an object to the array associated with a given key, only
       * if it is not already present in the array. The position of the insert is
       * not guaranteed.
       *
       * @param attr {String} The key.
       * @param item {} The object to add.
       */
      addUnique: function(attr, item) {
        return this.set(attr, new AV.Op.AddUnique(ensureArray(item)));
      },
  
      /**
       * Atomically remove all instances of an object from the array associated
       * with a given key.
       *
       * @param attr {String} The key.
       * @param item {} The object to remove.
       */
      remove: function(attr, item) {
        return this.set(attr, new AV.Op.Remove(ensureArray(item)));
      },
  
      /**
       * Atomically apply a "bit and" operation on the value associated with a
       * given key.
       *
       * @param attr {String} The key.
       * @param value {Number} The value to apply.
       */
      bitAnd(attr, value) {
        return this.set(attr, new AV.Op.BitAnd(value));
      },
  
      /**
       * Atomically apply a "bit or" operation on the value associated with a
       * given key.
       *
       * @param attr {String} The key.
       * @param value {Number} The value to apply.
       */
      bitOr(attr, value) {
        return this.set(attr, new AV.Op.BitOr(value));
      },
  
      /**
       * Atomically apply a "bit xor" operation on the value associated with a
       * given key.
       *
       * @param attr {String} The key.
       * @param value {Number} The value to apply.
       */
      bitXor(attr, value) {
        return this.set(attr, new AV.Op.BitXor(value));
      },
  
      /**
       * Returns an instance of a subclass of AV.Op describing what kind of
       * modification has been performed on this field since the last time it was
       * saved. For example, after calling object.increment("x"), calling
       * object.op("x") would return an instance of AV.Op.Increment.
       *
       * @param attr {String} The key.
       * @returns {AV.Op} The operation, or undefined if none.
       */
      op: function(attr) {
        return _.last(this._opSetQueue)[attr];
      },
  
      /**
       * Clear all attributes on the model, firing <code>"change"</code> unless
       * you choose to silence it.
       */
      clear: function(options) {
        options = options || {};
        options.unset = true;
        var keysToClear = _.extend(this.attributes, this._operations);
        return this.set(keysToClear, options);
      },
  
      /**
       * Returns a JSON-encoded set of operations to be sent with the next save
       * request.
       * @private
       */
      _getSaveJSON: function() {
        var json = _.clone(_.first(this._opSetQueue));
        AV._objectEach(json, function(op, key) {
          json[key] = op.toJSON();
        });
        return json;
      },
  
      /**
       * Returns true if this object can be serialized for saving.
       * @private
       */
      _canBeSerialized: function() {
        return AV.Object._canBeSerializedAsValue(this.attributes);
      },
  
      /**
       * Fetch the model from the server. If the server's representation of the
       * model differs from its current attributes, they will be overriden,
       * triggering a <code>"change"</code> event.
       * @param {Object} fetchOptions Optional options to set 'keys',
       *      'include' and 'includeACL' option.
       * @param {AuthOptions} options
       * @return {Promise} A promise that is fulfilled when the fetch
       *     completes.
       */
      fetch: function(fetchOptions, options) {
  
        var self = this;
        var request = _request('classes', this.className, this.id, 'GET',
                                  transformFetchOptions(fetchOptions), options);
        return request.then(function(response) {
          self._finishFetch(self.parse(response), true);
          return self;
        });
      },
  
      /**
       * Set a hash of model attributes, and save the model to the server.
       * updatedAt will be updated when the request returns.
       * You can either call it as:<pre>
       *   object.save();</pre>
       * or<pre>
       *   object.save(null, options);</pre>
       * or<pre>
       *   object.save(attrs, options);</pre>
       * or<pre>
       *   object.save(key, value, options);</pre>
       *
       * @example
       * gameTurn.save({
       *   player: "Jake Cutter",
       *   diceRoll: 2
       * }).then(function(gameTurnAgain) {
       *   // The save was successful.
       * }, function(error) {
       *   // The save failed.  Error is an instance of AVError.
       * });
       *
       * @param {AuthOptions} options AuthOptions plus:
       * @param {Boolean} options.fetchWhenSave fetch and update object after save succeeded
       * @param {AV.Query} options.query Save object only when it matches the query
       * @return {AV.Promise} A promise that is fulfilled when the save
       *     completes.
       * @see AVError
       */
      save: function(arg1, arg2, arg3) {
        var i, attrs, current, options, saved;
        if (_.isObject(arg1) || isNullOrUndefined(arg1)) {
          attrs = arg1;
          options = arg2;
        } else {
          attrs = {};
          attrs[arg1] = arg2;
          options = arg3;
        }
  
        options = _.clone(options) || {};
        if (options.wait) {
          current = _.clone(this.attributes);
        }
  
        var setOptions = _.clone(options) || {};
        if (setOptions.wait) {
          setOptions.silent = true;
        }
        if (attrs) {
          this.set(attrs, setOptions);
        }
  
        var model = this;
  
        var unsavedChildren = [];
        var unsavedFiles = [];
        AV.Object._findUnsavedChildren(model,
                                          unsavedChildren,
                                          unsavedFiles);
        if (unsavedChildren.length + unsavedFiles.length > 1) {
          return AV.Object._deepSaveAsync(this, model, options);
        }
  
        this._startSave();
        this._saving = (this._saving || 0) + 1;
  
        this._allPreviousSaves = this._allPreviousSaves || AV.Promise.resolve();
        this._allPreviousSaves = this._allPreviousSaves.catch(e => {}).then(function() {
          var method = model.id ? 'PUT' : 'POST';
  
          var json = model._getSaveJSON();
          var query = {};
  
          if(model._fetchWhenSave || options.fetchWhenSave){
            query['new'] = 'true';
          }
  
          if (options.query) {
            var queryJSON;
            if (typeof options.query.toJSON === 'function') {
              queryJSON = options.query.toJSON();
              if (queryJSON) {
                query.where = queryJSON.where;
              }
            }
            if (!query.where) {
              var error = new Error('options.query is not an AV.Query');
              throw error;
            }
          }
  
          _.extend(json, model._flags);
  
          var route = "classes";
          var className = model.className;
          if (model.className === "_User" && !model.id) {
            // Special-case user sign-up.
            route = "users";
            className = null;
          }
          //hook makeRequest in options.
          var makeRequest = options._makeRequest || _request;
          var requestPromise = makeRequest(route, className, model.id, method, json, options, query);
  
          requestPromise = requestPromise.then(function(resp) {
            var serverAttrs = model.parse(resp);
            if (options.wait) {
              serverAttrs = _.extend(attrs || {}, serverAttrs);
            }
            model._finishSave(serverAttrs);
            if (options.wait) {
              model.set(current, setOptions);
            }
            return model;
  
          }, function(error) {
            model._cancelSave();
            throw error;
          });
  
          return requestPromise;
        });
        return this._allPreviousSaves;
      },
  
      /**
       * Destroy this model on the server if it was already persisted.
       * Optimistically removes the model from its collection, if it has one.
       * @param {AuthOptions} options AuthOptions plus:
       * @param {Boolean} [options.wait] wait for the server to respond
       * before removal.
       *
       * @return {Promise} A promise that is fulfilled when the destroy
       *     completes.
       */
      destroy: function(options) {
        options = options || {};
        var model = this;
  
        var triggerDestroy = function() {
          model.trigger('destroy', model, model.collection, options);
        };
  
        if (!this.id) {
          return triggerDestroy();
        }
  
        if (!options.wait) {
          triggerDestroy();
        }
  
        var request =
            _request('classes', this.className, this.id, 'DELETE', this._flags, options);
        return request.then(function() {
          if (options.wait) {
            triggerDestroy();
          }
          return model;
        });
      },
  
      /**
       * Converts a response into the hash of attributes to be set on the model.
       * @ignore
       */
      parse: function(resp) {
        var output = _.clone(resp);
        _(["createdAt", "updatedAt"]).each(function(key) {
          if (output[key]) {
            output[key] = AV._parseDate(output[key]);
          }
        });
        if (output.createdAt && !output.updatedAt) {
          output.updatedAt = output.createdAt;
        }
        return output;
      },
  
      /**
       * Creates a new model with identical attributes to this one.
       * @return {AV.Object}
       */
      clone: function() {
        return new this.constructor(this.attributes);
      },
  
      /**
       * Returns true if this object has never been saved to AV.
       * @return {Boolean}
       */
      isNew: function() {
        return !this.id;
      },
  
      /**
       * Call this method to manually fire a `"change"` event for this model and
       * a `"change:attribute"` event for each changed attribute.
       * Calling this will cause all objects observing the model to update.
       */
      change: function(options) {
        options = options || {};
        var changing = this._changing;
        this._changing = true;
  
        // Silent changes become pending changes.
        var self = this;
        AV._objectEach(this._silent, function(attr) {
          self._pending[attr] = true;
        });
  
        // Silent changes are triggered.
        var changes = _.extend({}, options.changes, this._silent);
        this._silent = {};
        AV._objectEach(changes, function(unused_value, attr) {
          self.trigger('change:' + attr, self, self.get(attr), options);
        });
        if (changing) {
          return this;
        }
  
        // This is to get around lint not letting us make a function in a loop.
        var deleteChanged = function(value, attr) {
          if (!self._pending[attr] && !self._silent[attr]) {
            delete self.changed[attr];
          }
        };
  
        // Continue firing `"change"` events while there are pending changes.
        while (!_.isEmpty(this._pending)) {
          this._pending = {};
          this.trigger('change', this, options);
          // Pending and silent changes still remain.
          AV._objectEach(this.changed, deleteChanged);
          self._previousAttributes = _.clone(this.attributes);
        }
  
        this._changing = false;
        return this;
      },
  
      /**
       * Determine if the model has changed since the last <code>"change"</code>
       * event.  If you specify an attribute name, determine if that attribute
       * has changed.
       * @param {String} attr Optional attribute name
       * @return {Boolean}
       */
      hasChanged: function(attr) {
        if (!arguments.length) {
          return !_.isEmpty(this.changed);
        }
        return this.changed && _.has(this.changed, attr);
      },
  
      /**
       * Returns an object containing all the attributes that have changed, or
       * false if there are no changed attributes. Useful for determining what
       * parts of a view need to be updated and/or what attributes need to be
       * persisted to the server. Unset attributes will be set to undefined.
       * You can also pass an attributes object to diff against the model,
       * determining if there *would be* a change.
       */
      changedAttributes: function(diff) {
        if (!diff) {
          return this.hasChanged() ? _.clone(this.changed) : false;
        }
        var changed = {};
        var old = this._previousAttributes;
        AV._objectEach(diff, function(diffVal, attr) {
          if (!_.isEqual(old[attr], diffVal)) {
            changed[attr] = diffVal;
          }
        });
        return changed;
      },
  
      /**
       * Gets the previous value of an attribute, recorded at the time the last
       * <code>"change"</code> event was fired.
       * @param {String} attr Name of the attribute to get.
       */
      previous: function(attr) {
        if (!arguments.length || !this._previousAttributes) {
          return null;
        }
        return this._previousAttributes[attr];
      },
  
      /**
       * Gets all of the attributes of the model at the time of the previous
       * <code>"change"</code> event.
       * @return {Object}
       */
      previousAttributes: function() {
        return _.clone(this._previousAttributes);
      },
  
      /**
       * Checks if the model is currently in a valid state. It's only possible to
       * get into an *invalid* state if you're using silent changes.
       * @return {Boolean}
       */
      isValid: function() {
        try {
          this.validate(this.attributes);
        } catch (error) {
          return false;
        }
        return true;
      },
  
      /**
       * You should not call this function directly unless you subclass
       * <code>AV.Object</code>, in which case you can override this method
       * to provide additional validation on <code>set</code> and
       * <code>save</code>.  Your implementation should throw an Error if
       * the attrs is invalid
       *
       * @param {Object} attrs The current data to validate.
       * @see AV.Object#set
       */
      validate: function(attrs) {
        if (_.has(attrs, "ACL") && !(attrs.ACL instanceof AV.ACL)) {
          throw new AVError(AVError.OTHER_CAUSE,
                                 "ACL must be a AV.ACL.");
        }
      },
  
      /**
       * Run validation against a set of incoming attributes, returning `true`
       * if all is well. If a specific `error` callback has been passed,
       * call that instead of firing the general `"error"` event.
       * @private
       */
      _validate: function(attrs, options) {
        if (options.silent || !this.validate) {
          return;
        }
        attrs = _.extend({}, this.attributes, attrs);
        this.validate(attrs);
      },
  
      /**
       * Returns the ACL for this object.
       * @returns {AV.ACL} An instance of AV.ACL.
       * @see AV.Object#get
       */
      getACL: function() {
        return this.get("ACL");
      },
  
      /**
       * Sets the ACL to be used for this object.
       * @param {AV.ACL} acl An instance of AV.ACL.
       * @param {Object} options Optional Backbone-like options object to be
       *     passed in to set.
       * @return {AV.Object} self
       * @see AV.Object#set
       */
      setACL: function(acl, options) {
        return this.set("ACL", acl, options);
      },
  
      disableBeforeHook: function() {
        this.ignoreHook('beforeSave');
        this.ignoreHook('beforeUpdate');
        this.ignoreHook('beforeDelete');
      },
  
      disableAfterHook: function() {
        this.ignoreHook('afterSave');
        this.ignoreHook('afterUpdate');
        this.ignoreHook('afterDelete');
      },
  
      ignoreHook: function(hookName) {
        if (!_.contains(['beforeSave', 'afterSave', 'beforeUpdate', 'afterUpdate', 'beforeDelete', 'afterDelete'], hookName)) {
          console.trace('Unsupported hookName: ' + hookName);
        }
  
        if (!AV.hookKey) {
          console.trace('ignoreHook required hookKey');
        }
  
        if (!this._flags.__ignore_hooks) {
          this._flags.__ignore_hooks = [];
        }
  
        this._flags.__ignore_hooks.push(hookName);
      }
    });
  
     /**
      * Creates an instance of a subclass of AV.Object for the give classname
      * and id.
      * @param  {String} className The name of the AV class backing this model.
      * @param {String} id The object id of this model.
      * @return {AV.Object} A new subclass instance of AV.Object.
      */
     AV.Object.createWithoutData = function(className, id, hasData){
       var result = new AV.Object(className);
       result.id = id;
       result._hasData = hasData;
       return result;
     };
     /**
      * Delete objects in batch.
      * @param {AV.Object[]} objects The <code>AV.Object</code> array to be deleted.
      * @param {AuthOptions} options
      * @return {Promise} A promise that is fulfilled when the save
      *     completes.
      */
    AV.Object.destroyAll = function(objects, options = {}){
      if (!objects || objects.length === 0){
        return AV.Promise.resolve();
      }
      const objectsByClassNameAndFlags = _.groupBy(objects, object => JSON.stringify({
        className: object.className,
        flags: object._flags
      }));
      const body = {
        requests: _.map(objectsByClassNameAndFlags, objects => {
          const ids = _.map(objects, 'id').join(',');
          return {
            method: 'DELETE',
            path: `/1.1/classes/${objects[0].className}/${ids}`,
            body: objects[0]._flags
          }
        })
      };
      return _request('batch', null, null, 'POST', body, options).then(response => {
        const firstError = _.find(response, result => !result.success);
        if (firstError) throw new AVError(firstError.error.code, firstError.error.error);
        return undefined;
      });
    };
  
    /**
     * Returns the appropriate subclass for making new instances of the given
     * className string.
     * @private
     */
    AV.Object._getSubclass = function(className) {
      if (!_.isString(className)) {
        throw new Error('AV.Object._getSubclass requires a string argument.');
      }
      var ObjectClass = AV.Object._classMap[className];
      if (!ObjectClass) {
        ObjectClass = AV.Object.extend(className);
        AV.Object._classMap[className] = ObjectClass;
      }
      return ObjectClass;
    };
  
    /**
     * Creates an instance of a subclass of AV.Object for the given classname.
     * @private
     */
    AV.Object._create = function(className, attributes, options) {
      var ObjectClass = AV.Object._getSubclass(className);
      return new ObjectClass(attributes, options);
    };
  
    // Set up a map of className to class so that we can create new instances of
    // AV Objects from JSON automatically.
    AV.Object._classMap = {};
  
    AV.Object._extend = AV._extend;
  
    /**
     * Creates a new model with defined attributes,
     * It's the same with
     * <pre>
     *   new AV.Object(attributes, options);
     *  </pre>
     * @param {Object} attributes The initial set of data to store in the object.
     * @param {Object} options A set of Backbone-like options for creating the
     *     object.  The only option currently supported is "collection".
     * @return {AV.Object}
     * @since v0.4.4
     * @see AV.Object
     * @see AV.Object.extend
     */
    AV.Object['new'] = function(attributes, options){
      return new AV.Object(attributes, options);
    };
  
    /**
     * Creates a new subclass of AV.Object for the given AV class name.
     *
     * <p>Every extension of a AV class will inherit from the most recent
     * previous extension of that class. When a AV.Object is automatically
     * created by parsing JSON, it will use the most recent extension of that
     * class.</p>
     *
     * @example
     * var MyClass = AV.Object.extend("MyClass", {
     *     // Instance properties
     * }, {
     *     // Class properties
     * });
     *
     * @param {String} className The name of the AV class backing this model.
     * @param {Object} protoProps Instance properties to add to instances of the
     *     class returned from this method.
     * @param {Object} classProps Class properties to add the class returned from
     *     this method.
     * @return {Class} A new subclass of AV.Object.
     */
    AV.Object.extend = function(className, protoProps, classProps) {
      // Handle the case with only two args.
      if (!_.isString(className)) {
        if (className && _.has(className, "className")) {
          return AV.Object.extend(className.className, className, protoProps);
        } else {
          throw new Error(
              "AV.Object.extend's first argument should be the className.");
        }
      }
  
      // If someone tries to subclass "User", coerce it to the right type.
      if (className === "User") {
        className = "_User";
      }
  
      var NewClassObject = null;
      if (_.has(AV.Object._classMap, className)) {
        var OldClassObject = AV.Object._classMap[className];
        // This new subclass has been told to extend both from "this" and from
        // OldClassObject. This is multiple inheritance, which isn't supported.
        // For now, let's just pick one.
        if (protoProps || classProps) {
          NewClassObject = OldClassObject._extend(protoProps, classProps);
        } else {
          return OldClassObject;
        }
      } else {
        protoProps = protoProps || {};
        protoProps._className = className;
        NewClassObject = this._extend(protoProps, classProps);
      }
      // Extending a subclass should reuse the classname automatically.
      NewClassObject.extend = function(arg0) {
        if (_.isString(arg0) || (arg0 && _.has(arg0, "className"))) {
          return AV.Object.extend.apply(NewClassObject, arguments);
        }
        var newArguments = [className].concat(_.toArray(arguments));
        return AV.Object.extend.apply(NewClassObject, newArguments);
      };
      // Add the query property descriptor.
      Object.defineProperty(NewClassObject, 'query', Object.getOwnPropertyDescriptor(AV.Object, 'query'));
      NewClassObject['new'] = function (attributes, options) {
        return new NewClassObject(attributes, options);
      };
      AV.Object._classMap[className] = NewClassObject;
      return NewClassObject;
    };
  
    // ES6 class syntax support
    Object.defineProperty(AV.Object.prototype, 'className', {
      get: function() {
        const className = this._className || this.constructor._LCClassName || this.constructor.name;
        // If someone tries to subclass "User", coerce it to the right type.
        if (className === "User") {
          return "_User";
        }
        return className;
      },
    });
  
    /**
     * Register a class.
     * If a subclass of <code>AV.Object</code> is defined with your own implement
     * rather then <code>AV.Object.extend</code>, the subclass must be registered.
     * @param {Function} klass A subclass of <code>AV.Object</code>
     * @param {String} [name] Specify the name of the class. Useful when the class might be uglified.
     * @example
     * class Person extend AV.Object {}
     * AV.Object.register(Person);
     */
    AV.Object.register = (klass, name) => {
      if (!(klass.prototype instanceof AV.Object)) {
        throw new Error('registered class is not a subclass of AV.Object');
      }
      const className = name || klass.name;
      if (!className.length) {
        throw new Error('registered class must be named');
      }
      if (name) {
        klass._LCClassName = name;
      }
      AV.Object._classMap[className] = klass;
    };
  
    /**
     * Get a new Query of the current class
     * @name query
     * @memberof AV.Object
     * @type AV.Query
     * @readonly
     * @since v3.1.0
     * @example
     * const Post = AV.Object.extend('Post');
     * Post.query.equalTo('author', 'leancloud').find().then();
     */
    Object.defineProperty(AV.Object, 'query', {
      get() {
        return new AV.Query(this.prototype.className);
      },
    });
  
    AV.Object._findUnsavedChildren = function(objects, children, files) {
      AV._traverse(objects, function(object) {
        if (object instanceof AV.Object) {
          if (object._dirty()) {
            children.push(object);
          }
          return;
        }
  
        if (object instanceof AV.File) {
          if (!object.url() && !object.id) {
            files.push(object);
          }
          return;
        }
      });
    };
  
    AV.Object._canBeSerializedAsValue = function(object) {
      var canBeSerializedAsValue = true;
  
      if (object instanceof AV.Object || object instanceof AV.File) {
        canBeSerializedAsValue = !!object.id;
  
      } else if (_.isArray(object)) {
        AV._arrayEach(object, function(child) {
          if (!AV.Object._canBeSerializedAsValue(child)) {
            canBeSerializedAsValue = false;
          }
        });
  
      } else if (_.isObject(object)) {
        AV._objectEach(object, function(child) {
          if (!AV.Object._canBeSerializedAsValue(child)) {
            canBeSerializedAsValue = false;
          }
        });
      }
  
      return canBeSerializedAsValue;
    };
  
    AV.Object._deepSaveAsync = function(object, model, options) {
      var unsavedChildren = [];
      var unsavedFiles = [];
      AV.Object._findUnsavedChildren(object, unsavedChildren, unsavedFiles);
  
      var promise = AV.Promise.resolve();
      _.each(unsavedFiles, function(file) {
        promise = promise.then(function() {
          return file.save();
        });
      });
  
      var objects = _.uniq(unsavedChildren);
      var remaining = _.uniq(objects);
  
      return promise.then(function() {
        return AV.Promise._continueWhile(function() {
          return remaining.length > 0;
        }, function() {
  
          // Gather up all the objects that can be saved in this batch.
          var batch = [];
          var newRemaining = [];
          AV._arrayEach(remaining, function(object) {
            // Limit batches to 20 objects.
            if (batch.length > 20) {
              newRemaining.push(object);
              return;
            }
  
            if (object._canBeSerialized()) {
              batch.push(object);
            } else {
              newRemaining.push(object);
            }
          });
          remaining = newRemaining;
  
          // If we can't save any objects, there must be a circular reference.
          if (batch.length === 0) {
            return AV.Promise.reject(
              new AVError(AVError.OTHER_CAUSE,
                              "Tried to save a batch with a cycle."));
          }
  
          // Reserve a spot in every object's save queue.
          var readyToStart = AV.Promise.resolve(_.map(batch, function(object) {
            return object._allPreviousSaves || AV.Promise.resolve();
          }));
  
          // Save a single batch, whether previous saves succeeded or failed.
          const bathSavePromise = readyToStart.then(() =>
            _request("batch", null, null, "POST", {
              requests: _.map(batch, function(object) {
  
                var method = object.id ? 'PUT' : 'POST';
                
                var json = object._getSaveJSON();
                var query = {};
                    
                _.extend(json, object._flags);
        
                var route = "classes";
                var className = object.className;
                var path = `/${route}/${className}`;
                if (object.className === "_User" && !object.id) {
                  // Special-case user sign-up.
                  path = '/users';
                }
                
                var path = `/1.1${path}`;
                if (object.id) {
                  path = path + "/" + object.id;
                }
  
                object._startSave();
  
                return {
                  method: method,
                  path: path,
                  body: json
                };
              })
  
            }, options).then(function(response) {
              const results = _.map(batch, function(object, i) {
                if (response[i].success) {
                  object._finishSave(object.parse(response[i].success));
                  return object;
                }
                object._cancelSave();
                return new AVError(response[i].error.code, response[i].error.error);
              });
              return handleBatchResults(results);
            })
          );
          AV._arrayEach(batch, function(object) {
            object._allPreviousSaves = bathSavePromise;
          });
          return bathSavePromise;
        });
      }).then(function() {
        return object;
      });
    };
  
  };
  