/*
 * EventManager.js
 * by Keith Gaughan
 *
 * This allows event handlers to be registered unobtrusively, and cleans
 * them up on unload to prevent memory leaks.
 *
 * Copyright (c) Keith Gaughan, 2005.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Common Public License v1.0
 * (CPL) which accompanies this distribution, and is available at
 * http://www.opensource.org/licenses/cpl.php
 *
 * This software is covered by a modified version of the Common Public License
 * (CPL), where Keith Gaughan is the Agreement Steward, and the licensing
 * agreement is covered by the laws of the Republic of Ireland.
 */

// For implementations that don't include the push() methods for arrays.
if (!Array.prototype.push)
{
	 Array.prototype.push = function(elem)
	 {
		  this[this.length] = elem;
	 }
}

var EventManager =
{
	 _registry: null,

	 Initialise: function()
	 {
		  if (this._registry == null)
		  {
				this._registry = [];

				// Register the cleanup handler on page unload.
				EventManager.Add(window, "unload", this.CleanUp);
		  }
	 },

	 /**
	  * Registers an event and handler with the manager.
	  *
	  * @param  obj         Object handler will be attached to.
	  * @param  type        Name of event handler responds to.
	  * @param  fn          Handler function.
	  * @param  useCapture  Use event capture. False by default.
	  *                     If you don't understand this, ignore it.
	  *
	  * @return True if handler registered, else false.
	  */
	 Add: function(obj, type, fn, useCapture)
	 {
		  this.Initialise();

		  // If a string was passed in, it's an id.
		  if (typeof obj == "string")
				obj = document.getElementById(obj);
		  if (obj == null || fn == null)
				return false;

		  // Mozilla/W3C listeners?
		  if (obj.addEventListener)
		  {
				obj.addEventListener(type, fn, useCapture);
				this._registry.push({obj: obj, type: type, fn: fn, useCapture: useCapture});
				return true;
		  }

		  // IE-style listeners?
		  if (obj.attachEvent && obj.attachEvent("on" + type, fn))
		  {
				this._registry.push({obj: obj, type: type, fn: fn, useCapture: false});
				return true;
		  }

		  return false;
	 },

	 /**
	  * Cleans up all the registered event handlers.
	  */
	 CleanUp: function()
	 {
		  for (var i = 0; i < EventManager._registry.length; i++)
		  {
				with (EventManager._registry[i])
				{
					 // Mozilla/W3C listeners?
					 if (obj.removeEventListener)
						  obj.removeEventListener(type, fn, useCapture);
					 // IE-style listeners?
					 else if (obj.detachEvent)
						  obj.detachEvent("on" + type, fn);
				}
		  }

		  // Kill off the registry itself to get rid of the last remaining
		  // references.
		  EventManager._registry = null;
	 }
};