/*======================================================================
EventManager.js - Keith Gaughan
http://talideon.com/weblog/2005/03/js-memory-leaks.cfm

This allows event handlers to be registered unobtrusively, and cleans
them up on unload to prevent memory leaks.
======================================================================*/
//**************************************************
//
// Dependencies: mm.js, utils.js
//
//**************************************************

// 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 = getDOMElementByID(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;
    }
};