/**
 * JSTWEEN - TERMS OF USE
 * Copyright (c) 2008 Weston Pearce All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided the following conditions are 
 * met:
 *
 * Redistributions of source code must retain the above copyright 
 * notice, this list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright 
 * notice, this list of conditions and the following disclaimer in the 
 * documentation and/or other materials provided with the distribution.
 *
 * Neither the name of the author nor the names of contributors may be 
 * used to endorse or promote products derived from this software 
 * without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 
 * SUCH DAMAGE.
 */

/**
 * @projectDescription 	Javascript tween library.
 * @author				Weston Pearce wespear@gmail.com
 * @version				1.0
 */

/**
 * This class changes object properties over a period of frames using 
 * tweening formulae.
 * 
 * @param	{Object}	obj			The object to be manipulated.
 * @param	{String}	prop		The property to tween.
 * @param	{Function}	ease		The easing formula to use.
 * @param	{Number}	begin		The initial value of the tween.
 * @param	{Number}	end			The final value of the tween.
 * @param	{Number}	frames		The number of frames to animate over.
 * @param	{Function}	callback	A function to call on completion.
 * 
 * @return {JSTween} Returns a new JSTween.
 * @constructor
 */
Tween = function(obj, prop, ease, begin, end, frames, callback){

	/**
	 * The frame of the current animation.
	 * @alias Tween.frame
	 * @type {Integer}
	 */
	this.frame = 0;

	/** 
	 * The Interval running the animation.
	 * @alias Tween.running
	 * @type {Interval}
	 */
	this.running = null;

	/** 
	 * This method plays the animation.
	 * @alias Tween.play
	 * @method
	 */
	this.play = function(){
		this.running = setInterval(this.mechanism,5);
	}

	/** 
	 * This method stops the animation.
	 * @alias Tween.stop
	 * @method
	 */
	this.stop = function(){
		clearInterval(this.running);
		if(callback) callback();
	}

	// Closure variable
	var tween = this;

	/**
	 * This function progresses the animation 1 frame
	 * @alias Tween.mechanism
	 * @type {Function}
	 */
	this.mechanism = function(){
		obj[prop] = ease(tween.frame++, begin, end, frames);
		if(tween.frame > frames) tween.stop();
	}
}