define(
    [
        'jquery'
    ], function ($) {

        var parallaxElements = $('.para');

        var ticking = false;
        lastScrollY = $(window).scrollTop();

        function onResize() {
            updateElements();
            lastScrollY = $(window).scrollTop();
        }

        function onScroll(evt) {

            if (!ticking) {
                ticking = true;
                requestAnimFrame(updateElements);
                lastScrollY = $(window).scrollTop();
            }
        }

        function updateElements() {

            if (parallaxElements !== null) {
                parallaxElements.each(function (){

                    var limitMax = lastScrollY + $(window).height() + 50;
                    var limitMin = lastScrollY + $(window).height()/3;

                    if( $(this).offset().top > limitMin){
                        var pos = ($(this).offset().top - limitMin)/(limitMax - limitMin) * 35;
                        prefix($(this), "Transform", "translate3d(0, " + pos + "px, 0)");
                    }else{
                        prefix($(this), "Transform", "translate3d(0, 0, 0)");
                    }

                });
            }

            ticking = false;
        }


        function prefix(obj, prop, value) {
            var prefs = ['webkit', 'Moz', 'o', 'ms'];
            for (var pref in prefs) {
                obj.css( prefs[pref] + prop , value);
            }
        }

        // shim layer with setTimeout fallback
        window.requestAnimFrame = (function() {
            return window.requestAnimationFrame ||
                window.webkitRequestAnimationFrame ||
                window.mozRequestAnimationFrame ||
                window.oRequestAnimationFrame ||
                window.msRequestAnimationFrame ||
                function(callback) {
                    window.setTimeout(callback, 1000 / 60);
                };
        })();


        function initParallax() {
            updateElements();
            lastScrollY = $(window).scrollTop();
        }

        window.addEventListener('resize', onResize, false);
        window.addEventListener('scroll', onScroll, false);


        return {
            init: initParallax
        }
    });