/* rAF
 * ----------------------------------------------------------------------------
 * cross-browser (IE 8+) animation framework with easings
 *
 * url     : https://gist.github.com/imthenachoman/d19dc4cf6e53ad3664ea
 * author  : Anchal Nigam
 * e-mail  : imthenachoman@gmail.com
 *
 * Copyright (c) 2015 Anchal Nigam (imthenachoman@gmail.com)
 * Licensed under the MIT license: http://opensource.org/licenses/MIT
 * ----------------------------------------------------------------------------
 */
var animate = (function()
{
    // store each animation so we can cancel them later
    var animationCounter = 0, animationIDTracker = {};
    var lastTime = 0, vendors = ['ms', 'moz', 'webkit', 'o'];
    
    // easing functions
    var easingFunctions = {
        linear: function (t) { return t },
        easeInQuad: function (t) { return t*t },
        easeOutQuad: function (t) { return t*(2-t) },
        easeInOutQuad: function (t) { return t<.5 ? 2*t*t : -1+(4-2*t)*t },
        easeInCubic: function (t) { return t*t*t },
        easeOutCubic: function (t) { return (--t)*t*t+1 },
        easeInOutCubic: function (t) { return t<.5 ? 4*t*t*t : (t-1)*(2*t-2)*(2*t-2)+1 },
        easeInQuart: function (t) { return t*t*t*t },
        easeOutQuart: function (t) { return 1-(--t)*t*t*t },
        easeInOutQuart: function (t) { return t<.5 ? 8*t*t*t*t : 1-8*(--t)*t*t*t },
        easeInQuint: function (t) { return t*t*t*t*t },
        easeOutQuint: function (t) { return 1+(--t)*t*t*t*t },
        easeInOutQuint: function (t) { return t<.5 ? 16*t*t*t*t*t : 1+16*(--t)*t*t*t*t }
    };
    
    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x)
    {
        window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
        window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
    }
    
    if(!window.requestAnimationFrame)
        window.requestAnimationFrame = function(callback, element)
        {
            var currTime = new Date().getTime();
            var timeToCall = Math.max(0, 16 - (currTime - lastTime));
            var id = window.setTimeout(function()
            {
                callback(currTime + timeToCall);
            }, timeToCall);
            lastTime = currTime + timeToCall;
            return id;
        };
        
    if(!window.cancelAnimationFrame)
        window.cancelAnimationFrame = function(id)
        {
            clearTimeout(id);
        };
    
    // to animate
    return {
        // stop an animation
        "stop" : function(id)
        {
            cancelAnimationFrame(animationIDTracker[id]);
        },
        // start an animation
        // duration = time in milliseconds
        // action = function to call on each iteration; will be passed a rate paramater which equals to the percent complete (0 = starting; 1 = done)
        // easing is an optional easing function
        "start" : function(duration, action, easing)
        {
            var currentAnimationID = animationCounter++;
            var end = +new Date() + duration;
            var step = function()
            {
                var remaining = end - (+new Date());
                if( remaining < 60)
                {
                    action(1);
                    delete animationIDTracker[currentAnimationID];
                    return;
                }
                else
                {
                    action(1 - easingFunctions[easing || "linear"](remaining/duration));
                }
                animationIDTracker[currentAnimationID] = requestAnimationFrame(step);
            };
            step();
            return currentAnimationID;
        }
    };
})();

/*
 * References:
 *     - jquery style animations using requestAnimationFrame with easing
 *     - requestAnimationFrame - https://gist.github.com/paulirish/1579671
 *     - animations - http://www.sitepoint.com/simple-animations-using-requestanimationframe/
 *     - easing functions - https://gist.github.com/gre/1650294
 */