PubSub.js

define(['cluster/util'], function(util) {


  var PubSub = function() {
    this.listeners_ = [];
    this.listenersById_ = {};
    this.lastId_ = 0;
  };


  var shared_;
  PubSub.sharedPubSub = function() {
    if (!shared_) {
      shared_ = new PubSub();
    }
    return shared_;
  };


  PubSub.prototype.subscribe = function(eventName, callback, opt_context) {
    if (!(eventName in this.listeners_)) {
      this.listeners_[eventName] = [];
    }

    var id = this.lastId_++;
    this.listeners_[eventName].push(id);
    this.listenersById_[id] = [callback, opt_context || null];

    return id;
  };


  PubSub.prototype.unsubscribe = function(subscriptionId) {
    delete this.listenersById_[subscriptionId];
  };


  PubSub.prototype.publish = function(eventName, var_args) {
    var args = Array.prototype.slice.call(arguments, 1);
    var listeners = this.listeners_[eventName] || [];

    var cleanedListeners = [];
    util.forEach(listeners, function(subscriptionId) {
      var listenerAndContext = this.listenersById_[subscriptionId];
      if (!listenerAndContext) {
        return;
      }

      var listener = listenerAndContext[0];
      var context = listenerAndContext[1];
      listener.apply(context, args);

      cleanedListeners.push(subscriptionId);
    }, this);
    this.listeners_[eventName] = cleanedListeners;
  };


  return PubSub;
});