// Copyright 2005 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @fileoverview Implementation of EventTarget as defined by W3C DOM 2/3.
 *
 * @see ../demos/eventtarget.html
 */

/**
 * Namespace for events
 */
goog.provide('goog.events.EventTarget');

goog.require('goog.Disposable');
goog.require('goog.events');


/**
 * This implements the EventTarget interface as defined by W3C DOM 2/3. The
 * main difference from the spec is that the this does not know about event
 * propagation and therefore the flag whether to use bubbling or capturing is
 * not used.
 *
 * Another difference is that event objects do not really have to implement
 * the Event interface. An object is treated as an event object if it has a
 * type property.
 *
 * It also allows you to pass a string instead of an event object and in that
 * case an event like object is created with the type set to the string value.
 *
 * Unless propagation is stopped, events dispatched by an EventTarget bubble
 * to its parent event target, returned by <code>getParentEventTarget</code>.
 * To set the parent event target, call <code>setParentEventTarget</code> or
 * override <code>getParentEventTarget</code> in a subclass.  Subclasses that
 * don't support changing the parent event target should override the setter
 * to throw an error.
 *
 * Example usage:
 * <pre>
 *   var et = new goog.events.EventTarget;
 *   function f(e) {
 *      alert("Type: " + e.type + "\nTarget: " + e.target);
 *   }
 *   et.addEventListener("foo", f);
 *   ...
 *   et.dispatchEvent({type: "foo"}); // will call f
 *   // or et.dispatchEvent("foo");
 *   ...
 *   et.removeEventListener("foo", f);
 *
 *  // You can also use the EventHandler interface:
 *  var eh = {
 *    handleEvent: function(e) {
 *      ...
 *    }
 * @constructor
 * @extends {goog.Disposable}
 */
goog.events.EventTarget = function() {
  goog.Disposable.call(this);
};
goog.inherits(goog.events.EventTarget, goog.Disposable);


/**
 * Used to tell if an event is a real event in goog.events.listen() so we don't
 * get listen() calling addEventListener() and vice-versa.
 * @type {boolean}
 * @private
 */
goog.events.EventTarget.prototype.customEvent_ = true;


/**
 * Parent event target, used during event bubbling.
 * @type {goog.events.EventTarget?}
 * @private
 */
goog.events.EventTarget.prototype.parentEventTarget_ = null;


/**
 * Returns the parent of this event target to use for bubbling.
 *
 * @return {goog.events.EventTarget} The parent EventTarget or null if there
 * is no parent.
 */
goog.events.EventTarget.prototype.getParentEventTarget = function() {
  return this.parentEventTarget_;
};


/**
 * Sets the parent of this event target to use for bubbling.
 *
 * @param {goog.events.EventTarget?} parent Parent EventTarget (null if none).
 */
goog.events.EventTarget.prototype.setParentEventTarget = function(parent) {
  this.parentEventTarget_ = parent;
};


/**
 * Adds an event listener to the event target. The same handler can only be
 * added once per the type. Even if you add the same handler multiple times
 * using the same type then it will only be called once when the event is
 * dispatched.
 *
 * Supported for legacy but use goog.events.listen(src, type, handler) instead.
 *
 * @param {string} type The type of the event to listen for.
 * @param {Function|Object} handler The function to handle the event. The
 *     handler can also be an object that implements the handleEvent method
 *     which takes the event object as argument.
 * @param {boolean=} opt_capture In DOM-compliant browsers, this determines
 *     whether the listener is fired during the capture or bubble phase
 *     of the event.
 * @param {Object=} opt_handlerScope Object in whose scope to call the listener.
 */
goog.events.EventTarget.prototype.addEventListener = function(
    type, handler, opt_capture, opt_handlerScope) {
  goog.events.listen(this, type, handler, opt_capture, opt_handlerScope);
};


/**
 * Removes an event listener from the event target. The handler must be the
 * same object as the one added. If the handler has not been added then
 * nothing is done.
 * @param {string} type The type of the event to listen for.
 * @param {Function|Object} handler The function to handle the event. The
 *     handler can also be an object that implements the handleEvent method
 *     which takes the event object as argument.
 * @param {boolean=} opt_capture In DOM-compliant browsers, this determines
 *     whether the listener is fired during the capture or bubble phase
 *     of the event.
 * @param {Object=} opt_handlerScope Object in whose scope to call the listener.
 */
goog.events.EventTarget.prototype.removeEventListener = function(
    type, handler, opt_capture, opt_handlerScope) {
  goog.events.unlisten(this, type, handler, opt_capture, opt_handlerScope);
};


/**
 * Dispatches an event (or event like object) and calls all listeners
 * listening for events of this type. The type of the event is decided by the
 * type property on the event object.
 *
 * If any of the listeners returns false OR calls preventDefault then this
 * function will return false.  If one of the capture listeners calls
 * stopPropagation, then the bubble listeners won't fire.
 *
 * @param {string|Object|goog.events.Event} e Event object.
 * @return {boolean} If anyone called preventDefault on the event object (or
 *     if any of the handlers returns false this will also return false.
 */
goog.events.EventTarget.prototype.dispatchEvent = function(e) {
  return goog.events.dispatchEvent(this, e);
};


/**
 * Unattach listeners from this object.  Classes that extend EventTarget may
 * need to override this method in order to remove references to DOM Elements
 * and additional listeners, it should be something like this:
 * <pre>
 * MyClass.prototype.disposeInternal = function() {
 *   MyClass.superClass_.disposeInternal.call(this);
 *   // Dispose logic for MyClass
 * };
 * </pre>
 * @protected
 */
goog.events.EventTarget.prototype.disposeInternal = function() {
  goog.events.EventTarget.superClass_.disposeInternal.call(this);
  goog.events.removeAll(this);
  this.parentEventTarget_ = null;
};
 *  };
 *  et.addEventListener("bar", eh);
 * </pre>
 *