(function(){
    // Back to Top - by CodyHouse.co
	var backTop = document.getElementsByClassName('js-cd-top')[0],
		// browser window scroll (in pixels) after which the "back to top" link is shown
		offset = 300,
		//browser window scroll (in pixels) after which the "back to top" link opacity is reduced
		offsetOpacity = 1200,
		scrollDuration = 700,
		scrolling = false;
	if( backTop ) {
		//update back to top visibility on scrolling
		window.addEventListener("scroll", function(event) {
			if( !scrolling ) {
				scrolling = true;
				(!window.requestAnimationFrame) ? setTimeout(checkBackToTop, 250) : window.requestAnimationFrame(checkBackToTop);
			}
		});
		//smooth scroll to top
		backTop.addEventListener('click', function(event) {
			event.preventDefault();
			(!window.requestAnimationFrame) ? window.scrollTo(0, 0) : scrollTop(scrollDuration);
		});
	}

	function checkBackToTop() {
		var windowTop = window.scrollY || document.documentElement.scrollTop;
		( windowTop > offset ) ? addClass(backTop, 'cd-top--show') : removeClass(backTop, 'cd-top--show', 'cd-top--fade-out');
		( windowTop > offsetOpacity ) && addClass(backTop, 'cd-top--fade-out');
		scrolling = false;
	}
	
	function scrollTop(duration) {
	    var start = window.scrollY || document.documentElement.scrollTop,
	        currentTime = null;
	        
	    var animateScroll = function(timestamp){
	    	if (!currentTime) currentTime = timestamp;        
	        var progress = timestamp - currentTime;
	        var val = Math.max(Math.easeInOutQuad(progress, start, -start, duration), 0);
	        window.scrollTo(0, val);
	        if(progress < duration) {
	            window.requestAnimationFrame(animateScroll);
	        }
	    };

	    window.requestAnimationFrame(animateScroll);
	}

	Math.easeInOutQuad = function (t, b, c, d) {
 		t /= d/2;
		if (t < 1) return c/2*t*t + b;
		t--;
		return -c/2 * (t*(t-2) - 1) + b;
	};

	//class manipulations - needed if classList is not supported
	function hasClass(el, className) {
	  	if (el.classList) return el.classList.contains(className);
	  	else return !!el.className.match(new RegExp('(\\s|^)' + className + '(\\s|$)'));
	}
	function addClass(el, className) {
		var classList = className.split(' ');
	 	if (el.classList) el.classList.add(classList[0]);
	 	else if (!hasClass(el, classList[0])) el.className += " " + classList[0];
	 	if (classList.length > 1) addClass(el, classList.slice(1).join(' '));
	}
	function removeClass(el, className) {
		var classList = className.split(' ');
	  	if (el.classList) el.classList.remove(classList[0]);	
	  	else if(hasClass(el, classList[0])) {
	  		var reg = new RegExp('(\\s|^)' + classList[0] + '(\\s|$)');
	  		el.className=el.className.replace(reg, ' ');
	  	}
	  	if (classList.length > 1) removeClass(el, classList.slice(1).join(' '));
	}
})();