text: /**
   * @license
   * Copyright 2016 Google Inc.
   *
   * 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.
   */
  
  goog.provide('shaka.util.EventManager');
  
  goog.require('goog.asserts');
  goog.require('shaka.util.IDestroyable');
  goog.require('shaka.util.MultiMap');
  
  
  
  /**
   * Creates a new EventManager. An EventManager maintains a collection of "event
   * bindings" between event targets and event listeners.
   *
   * @struct
   * @constructor
   * @implements {shaka.util.IDestroyable}
   */
  shaka.util.EventManager = function() {
    /**
     * Maps an event type to an array of event bindings.
     * @private {shaka.util.MultiMap.<!shaka.util.EventManager.Binding_>}
     */
    this.bindingMap_ = new shaka.util.MultiMap();
  };
  
  
  /**
   * @typedef {function(!Event)}
   */
  shaka.util.EventManager.ListenerType;
  
  
  /**
   * Detaches all event listeners.
   * @override
   */
  shaka.util.EventManager.prototype.destroy = function() {
    this.removeAll();
    this.bindingMap_ = null;
    return Promise.resolve();
  };
  
  
  /**
   * Attaches an event listener to an event target.
   * @param {EventTarget} target The event target.
   * @param {string} type The event type.
   * @param {shaka.util.EventManager.ListenerType} listener The event listener.
   */
  shaka.util.EventManager.prototype.listen = function(target, type, listener) {
    if (!this.bindingMap_) return;
  
    var binding = new shaka.util.EventManager.Binding_(target, type, listener);
    this.bindingMap_.push(type, binding);
  };
  
  
  /**
   * Attaches an event listener to an event target.  The listener will be removed
   * when the first instance of the event is fired.
   * @param {EventTarget} target The event target.
   * @param {string} type The event type.
   * @param {shaka.util.EventManager.ListenerType} listener The event listener.
   */
  shaka.util.EventManager.prototype.listenOnce =
      function(target, type, listener) {
    // Install a shim listener that will stop listening after the first event.
    this.listen(target, type, function(event) {
      // Stop listening to this event.
      this.unlisten(target, type);
      // Call the original listener.
      listener(event);
    }.bind(this));
  };
  
  
  /**
   * Detaches an event listener from an event target.
   * @param {EventTarget} target The event target.
   * @param {string} type The event type.
   */
  shaka.util.EventManager.prototype.unlisten = function(target, type) {
    if (!this.bindingMap_) return;
  
    var list = this.bindingMap_.get(type) || [];
  
    for (var i = 0; i < list.length; ++i) {
      var binding = list[i];
  
      if (binding.target == target) {
        binding.unlisten();
        this.bindingMap_.remove(type, binding);
      }
    }
  };
  
  
  /**
   * Detaches all event listeners from all targets.
   */
  shaka.util.EventManager.prototype.removeAll = function() {
    if (!this.bindingMap_) return;
  
    var list = this.bindingMap_.getAll();
  
    for (var i = 0; i < list.length; ++i) {
      list[i].unlisten();
    }
  
    this.bindingMap_.clear();
  };
  
  
  
  /**
   * Creates a new Binding_ and attaches the event listener to the event target.
   * @param {EventTarget} target The event target.
   * @param {string} type The event type.
   * @param {shaka.util.EventManager.ListenerType} listener The event listener.
   * @constructor
   * @private
   */
  shaka.util.EventManager.Binding_ = function(target, type, listener) {
    /** @type {EventTarget} */
    this.target = target;
  
    /** @type {string} */
    this.type = type;
  
    /** @type {?shaka.util.EventManager.ListenerType} */
    this.listener = listener;
  
    this.target.addEventListener(type, listener, false);
  };
  
  
  /**
   * Detaches the event listener from the event target. This does nothing if the
   * event listener is already detached.
   */
  shaka.util.EventManager.Binding_.prototype.unlisten = function() {
    goog.asserts.assert(this.target, 'Missing target');
    this.target.removeEventListener(this.type, this.listener, false);
  
    this.target = null;
    this.listener = null;
  };
  
  