var Timer = function(millis, callback){
	return this._init(millis, callback);
}

Timer.prototype = {
	_init: function(millis, callback){
		this._interval = 1000;
		this._timer = null;
		this._cbs = [];
		this._multipliers = [];
		this._tickCounts = [];
		this._canRun = [];
		this._stoppedThreads = 0;
		this._runOnce = false;
		this._startedAt = -1;
		this._pausedAt = -1;

		if(typeof(millis)=='number') this._interval = millis;
		this.addCallback(callback);
		return this;
	},

	_preset: function(){
		this._stoppedThreads = 0;
		this._startedAt = -1;
		this._pausedAt = -1;
		for(var i=0; i<this._cbs.length; i++){
			this._canRun[i] = true;
			this._tickCounts[i] = 0;
		}
	},

	_ticks: function(initInterval){
		var me = this;
		for(var i=0; i<this._cbs.length; i++){
			if(typeof(this._cbs[i])=='function' && this._canRun[i]){
				this._tickCounts[i]++;
				if(this._tickCounts[i] == this._multipliers[i]){
					this._tickCounts[i] = 0;
					if(this.runOnce()){
						this._canRun[i] = false;
						this._stoppedThreads++;
					}
					window.setTimeout(me._cbs[i], 0);
				}
			}
		}

		if(this.runOnce() && this._stoppedThreads == this._cbs.length)
			this.stop();
		if(typeof(initInterval)=='number') {
			this.stop().start(null, true);
		}
	},

	runOnce: function(isRunOnce){
		if(typeof(isRunOnce)=='undefined') return this._runOnce;
		else if(typeof(isRunOnce)=='boolean') this._runOnce = isRunOnce;
		else alert("Invalid argument for runOnce(...).\n\nUsage: runOnce(true | false) /*Default value: false*/\nor, runOnce() to get status");
		return this;
	},

	interval: function(millis){

		if(typeof(millis)=='undefined') return this._interval;

		else if(typeof(millis)=='number') this._interval = Math.floor(millis);

		return this;

	},

	stop: function(isPausing){

		if(this._timer){
			if(!isPausing) this._pausedAt = -1;
			try {
				window.clearInterval(this._timer);
			} catch(ex) {
			}
			this._timer = null;
		}
		return this;
	},

	isStopped: function(){
		return ((this._timer == null) && !this.isPaused());
	},

	start: function(_initialInterval, _withoutPreset){
		if(this.isPaused())
			return this.resume();
		if(!this.isStopped())
			return this;
		if(!_withoutPreset)
			this._preset();
		var tmpInterval = this._interval;
		if(typeof(_initialInterval)=='number') tmpInterval = _initialInterval;
		
		var me = this;

		this._timer = window.setInterval(function(){me._ticks(_initialInterval);}, tmpInterval);
		this._startedAt = (new Date()).getTime();
		this._startedAt -= (this._interval - tmpInterval);
		return this;
	},

	pause: function(){
		if(this._timer){
			this._pausedAt = (new Date()).getTime();
			this.stop(true);
		}
		return this;
	},

	isPaused: function(){
		return (this._pausedAt >= 0);	
	},

	resume: function(){
		if(this.isPaused()){
			var tempInterval = this._interval - ((this._pausedAt - this._startedAt)%this._interval);
			this._pausedAt = -1;
			this.start(tempInterval, true);
		}
		return this;
	},

	restart: function(){
		return this.stop().start();
	},

	addCallback: function(callback, N){
		if(typeof(callback)=='function'){
			this._cbs.push(callback);
			if(typeof(N)=='number'){
				N = Math.floor(N)
				this._multipliers.push((N < 1 ? 1 : N));
			} else
				this._multipliers.push(1);

			this._tickCounts.push(0);
			this._canRun.push(true);
		}
		return this;
	},

	clearCallbacks: function(){
		this._cbs.length = 0;
		this._multipliers.length = 0;
		this._canRun.length = 0;
		this._tickCounts.length = 0;
		this._stoppedThreads = 0;
		return this;
	}
};