/**
 * |-------------------|
 * | Backbone-Mediator |
 * |-------------------|
 *  Backbone-Mediator is freely distributable under the MIT license.
 *
 *  <a href="https://github.com/chalbert/Backbone-Mediator">More details & documentation</a>
 *
 * @author Nicolas Gilbert
 *
 * @requires _
 * @requires Backbone
 */
(function(factory){
  'use strict';

  if (typeof define === 'function' && define.amd) {
    define(['underscore', 'backbone'], factory);
  } else {
    factory(_, Backbone);
  }

})(function (_, Backbone){
  'use strict';

  /**
   * @static
   */
  var channels = {},
      Subscriber,
      /** @borrows Backbone.View#delegateEvents */
      delegateEvents = Backbone.View.prototype.delegateEvents,
      /** @borrows Backbone.View#delegateEvents */
      undelegateEvents = Backbone.View.prototype.undelegateEvents;

  /**
   * @class
   */
  Backbone.Mediator = {

    /**
     * Subscribe to a channel
     *
     * @param channel
     */
    subscribe: function(channel, subscription, context, once) {
      if (!channels[channel]) channels[channel] = [];
      channels[channel].push({fn: subscription, context: context || this, once: once});
    },

    /**
     * Trigger all callbacks for a channel
     *
     * @param channel
     * @params N Extra parametter to pass to handler
     */
    publish: function(channel) {
      if (!channels[channel]) return;

      var args = [].slice.call(arguments, 1),
          subscription;

      for (var i = 0; i < channels[channel].length; i++) {
        subscription = channels[channel][i];
        subscription.fn.apply(subscription.context, args);
        if (subscription.once) {
          Backbone.Mediator.unsubscribe(channel, subscription.fn, subscription.context);
          i--;
        }
      }
    },

    /**
     * Cancel subscription
     *
     * @param channel
     * @param fn
     * @param context
     */

    unsubscribe: function(channel, fn, context){
      if (!channels[channel]) return;

      var subscription;
      for (var i = 0; i < channels[channel].length; i++) {
        subscription = channels[channel][i];
        if (subscription.fn === fn && subscription.context === context) {
          channels[channel].splice(i, 1);
          i--;
        }
      }
    },

    /**
     * Subscribing to one event only
     *
     * @param channel
     * @param subscription
     * @param context
     */
    subscribeOnce: function (channel, subscription, context) {
      Backbone.Mediator.subscribe(channel, subscription, context, true);
    }

  };
  
  Backbone.Mediator.channels = channels;

  /**
   * Allow to define convention-based subscriptions
   * as an 'subscriptions' hash on a view. Subscriptions
   * can then be easily setup and cleaned.
   *
   * @class
   */


  Subscriber = {

    /**
     * Extend delegateEvents() to set subscriptions
     */
    delegateEvents: function(){
      delegateEvents.apply(this, arguments);
      this.setSubscriptions();
    },

    /**
     * Extend undelegateEvents() to unset subscriptions
     */
    undelegateEvents: function(){
      undelegateEvents.apply(this, arguments);
      this.unsetSubscriptions();
    },

    /** @property {Object} List of subscriptions, to be defined */
    subscriptions: {},

    /**
     * Subscribe to each subscription
     * @param {Object} [subscriptions] An optional hash of subscription to add
     */

    setSubscriptions: function(subscriptions){
      if (subscriptions) _.extend(this.subscriptions || {}, subscriptions);
      subscriptions = subscriptions || this.subscriptions;
      if (!subscriptions || _.isEmpty(subscriptions)) return;
      // Just to be sure we don't set duplicate
      this.unsetSubscriptions(subscriptions);

      _.each(subscriptions, function(subscription, channel){
        var once;
        if (subscription.$once) {
          subscription = subscription.$once;
          once = true;
        }
        if (_.isString(subscription)) {
          subscription = this[subscription];
        }
        Backbone.Mediator.subscribe(channel, subscription, this, once);
      }, this);
    },

    /**
     * Unsubscribe to each subscription
     * @param {Object} [subscriptions] An optional hash of subscription to remove
     */
    unsetSubscriptions: function(subscriptions){
      subscriptions = subscriptions || this.subscriptions;
      if (!subscriptions || _.isEmpty(subscriptions)) return;
      _.each(subscriptions, function(subscription, channel){
        if (_.isString(subscription)) {
          subscription = this[subscription];
        }
        Backbone.Mediator.unsubscribe(channel, subscription.$once || subscription, this);
      }, this);
    }
  };

  /**
   * @lends Backbone.View.prototype
   */
  _.extend(Backbone.View.prototype, Subscriber);

  /**
   * @lends Backbone.Mediator
   */
  _.extend(Backbone.Mediator, {
    /**
     * Shortcut for publish
     * @function
     */
    pub: Backbone.Mediator.publish,
    /**
     * Shortcut for subscribe
     * @function
     */
    sub: Backbone.Mediator.subscribe
  });

  return Backbone;

});