/*
Script: Fx.js
	Contains the basic animation logic to be extended by all other Fx Classes.

License:
	MIT-style license.
*/

var Fx = new Class({

	Implements: [Chain, Events, Options],

	options: {
		/*
		onStart: $empty,
		onCancel: $empty,
		onComplete: $empty,
		*/
		fps: 50,
		unit: false,
		duration: 500,
		link: 'ignore',
		transition: function(p){
			return -(Math.cos(Math.PI * p) - 1) / 2;
		}
	},

	initialize: function(options){
		this.subject = this.subject || this;
		this.setOptions(options);
		this.options.duration = Fx.Durations[this.options.duration] || this.options.duration.toInt();
		var wait = this.options.wait;
		if (wait === false) this.options.link = 'cancel';
	},

	step: function(){
		var time = $time();
		if (time < this.time + this.options.duration){
			var delta = this.options.transition((time - this.time) / this.options.duration);
			this.set(this.compute(this.from, this.to, delta));
		} else {
			this.set(this.compute(this.from, this.to, 1));
			this.complete();
		}
	},

	set: function(now){
		return now;
	},

	compute: function(from, to, delta){
		return Fx.compute(from, to, delta);
	},

	check: function(caller){
		if (!this.timer) return true;
		switch (this.options.link){
			case 'cancel': this.cancel(); return true;
			case 'chain': this.chain(caller.bind(this, Array.slice(arguments, 1))); return false;
		}
		return false;
	},

	start: function(from, to){
		if (!this.check(arguments.callee, from, to)) return this;
		this.from = from;
		this.to = to;
		this.time = 0;
		this.startTimer();
		this.onStart();
		return this;
	},

	complete: function(){
		if (this.stopTimer()) this.onComplete();
		return this;
	},

	cancel: function(){
		if (this.stopTimer()) this.onCancel();
		return this;
	},

	onStart: function(){
		this.fireEvent('start', this.subject);
	},

	onComplete: function(){
		this.fireEvent('complete', this.subject);
		if (!this.callChain()) this.fireEvent('chainComplete', this.subject);
	},

	onCancel: function(){
		this.fireEvent('cancel', this.subject).clearChain();
	},

	pause: function(){
		this.stopTimer();
		return this;
	},

	resume: function(){
		this.startTimer();
		return this;
	},

	stopTimer: function(){
		if (!this.timer) return false;
		this.time = $time() - this.time;
		this.timer = $clear(this.timer);
		return true;
	},

	startTimer: function(){
		if (this.timer) return false;
		this.time = $time() - this.time;
		this.timer = this.step.periodical(Math.round(1000 / this.options.fps), this);
		return true;
	}

});

Fx.compute = function(from, to, delta){
	return (to - from) * delta + from;
};

Fx.Durations = {'short': 250, 'normal': 500, 'long': 1000};