/**
 * @namespace fabric.Collection
 */
fabric.Collection = {

  _objects: [],

  /**
   * Adds objects to collection, Canvas or Group, then renders canvas
   * (if `renderOnAddRemove` is not `false`).
   * in case of Group no changes to bounding box are made.
   * Objects should be instances of (or inherit from) fabric.Object
   * Use of this function is highly discouraged for groups.
   * you can add a bunch of objects with the add method but then you NEED
   * to run a addWithUpdate call for the Group class or position/bbox will be wrong.
   * @param {...fabric.Object} object Zero or more fabric instances
   * @return {Self} thisArg
   * @chainable
   */
  add: function () {
    this._objects.push.apply(this._objects, arguments);
    if (this._onObjectAdded) {
      for (var i = 0, length = arguments.length; i < length; i++) {
        this._onObjectAdded(arguments[i]);
      }
    }
    this.renderOnAddRemove && this.requestRenderAll();
    return this;
  },

  /**
   * Inserts an object into collection at specified index, then renders canvas (if `renderOnAddRemove` is not `false`)
   * An object should be an instance of (or inherit from) fabric.Object
   * Use of this function is highly discouraged for groups.
   * you can add a bunch of objects with the insertAt method but then you NEED
   * to run a addWithUpdate call for the Group class or position/bbox will be wrong.
   * @param {Object} object Object to insert
   * @param {Number} index Index to insert object at
   * @param {Boolean} nonSplicing When `true`, no splicing (shifting) of objects occurs
   * @return {Self} thisArg
   * @chainable
   */
  insertAt: function (object, index, nonSplicing) {
    var objects = this._objects;
    if (nonSplicing) {
      objects[index] = object;
    }
    else {
      objects.splice(index, 0, object);
    }
    this._onObjectAdded && this._onObjectAdded(object);
    this.renderOnAddRemove && this.requestRenderAll();
    return this;
  },

  /**
   * Removes objects from a collection, then renders canvas (if `renderOnAddRemove` is not `false`)
   * @param {...fabric.Object} object Zero or more fabric instances
   * @return {Self} thisArg
   * @chainable
   */
  remove: function() {
    var objects = this._objects,
        index, somethingRemoved = false;

    for (var i = 0, length = arguments.length; i < length; i++) {
      index = objects.indexOf(arguments[i]);

      // only call onObjectRemoved if an object was actually removed
      if (index !== -1) {
        somethingRemoved = true;
        objects.splice(index, 1);
        this._onObjectRemoved && this._onObjectRemoved(arguments[i]);
      }
    }

    this.renderOnAddRemove && somethingRemoved && this.requestRenderAll();
    return this;
  },

  /**
   * Executes given function for each object in this group
   * @param {Function} callback
   *                   Callback invoked with current object as first argument,
   *                   index - as second and an array of all objects - as third.
   *                   Callback is invoked in a context of Global Object (e.g. `window`)
   *                   when no `context` argument is given
   *
   * @param {Object} context Context (aka thisObject)
   * @return {Self} thisArg
   * @chainable
   */
  forEachObject: function(callback, context) {
    var objects = this.getObjects();
    for (var i = 0, len = objects.length; i < len; i++) {
      callback.call(context, objects[i], i, objects);
    }
    return this;
  },

  /**
   * Returns an array of children objects of this instance
   * Type parameter introduced in 1.3.10
   * since 2.3.5 this method return always a COPY of the array;
   * @param {String} [type] When specified, only objects of this type are returned
   * @return {Array}
   */
  getObjects: function(type) {
    if (typeof type === 'undefined') {
      return this._objects.concat();
    }
    return this._objects.filter(function(o) {
      return o.type === type;
    });
  },

  /**
   * Returns object at specified index
   * @param {Number} index
   * @return {Self} thisArg
   */
  item: function (index) {
    return this._objects[index];
  },

  /**
   * Returns true if collection contains no objects
   * @return {Boolean} true if collection is empty
   */
  isEmpty: function () {
    return this._objects.length === 0;
  },

  /**
   * Returns a size of a collection (i.e: length of an array containing its objects)
   * @return {Number} Collection size
   */
  size: function() {
    return this._objects.length;
  },

  /**
   * Returns true if collection contains an object
   * @param {Object} object Object to check against
   * @return {Boolean} `true` if collection contains an object
   */
  contains: function(object) {
    return this._objects.indexOf(object) > -1;
  },

  /**
   * Returns number representation of a collection complexity
   * @return {Number} complexity
   */
  complexity: function () {
    return this._objects.reduce(function (memo, current) {
      memo += current.complexity ? current.complexity() : 0;
      return memo;
    }, 0);
  }
};