//First the variables our app is going to use need to be declared

	//References to DOM elements
	var $window = $(window);
	var $document = $(document);
	//Only links that starts with #
	var $navButtons = $("nav a").filter("[href^=#]");
	var $navGoPrev = $(".go-prev");
	var $navGoNext = $(".go-next");
	var $slidesContainer = $(".slides-container");
	var $slides = $(".slide");
	var $currentSlide = $slides.first();

	//Animating flag - is our app animating
	var isAnimating = false;

	//The height of the window
	var pageHeight = $window.innerHeight();

	//Key codes for up and down arrows on keyboard. We'll be using this to navigate change slides using the keyboard
	var keyCodes = {
		UP  : 38,
		DOWN: 40
	}
  

var circles = $(".circle");

// Create animation for each element
var animations = circles.map(createAnimation);

function playAnimation(target) {
  
  // Cycle through list of animations
  animations.each(function(i, animate) {
    animate(target);
  });
}

function createAnimation(i, element) {
  
  var tween = TweenLite.to(element, 2, { x: 400, backgroundColor: "#673AB7", paused: true });
    
  return function(target) {
    
    if (element !== target) {
      tween.pause(0);
    } else {
      tween.play(0);      
    }
  }
}


	//Going to the first slide
	goToSlide($currentSlide);


	/*
	*   Adding event listeners
	* */

	$window.on("resize", onResize).resize();
	$window.on("mousewheel DOMMouseScroll", onMouseWheel);
	$document.on("keydown", onKeyDown);
	$navButtons.on("click", onNavButtonClick);
	$navGoPrev.on("click", goToPrevSlide);
	$navGoNext.on("click", goToNextSlide);



	/*
	*   Internal functions
	* */


	/*
	*   When a button is clicked - first get the button href, and then slide to the container, if there's such a container
	* */
	function onNavButtonClick(event)
	{
		//The clicked button
		var $button = $(this);

		//The slide the button points to
		var $slide = $($button.attr("href"));

		//If the slide exists, we go to it
		if($slide.length)
		{
			goToSlide($slide);
			event.preventDefault();
		}
	}

	/*
	*   Getting the pressed key. Only if it's up or down arrow, we go to prev or next slide and prevent default behaviour
	*   This way, if there's text input, the user is still able to fill it
	* */
	function onKeyDown(event)
	{

		var PRESSED_KEY = event.keyCode;

		if(PRESSED_KEY == keyCodes.UP)
		{
			goToPrevSlide();
			event.preventDefault();
		}
		else if(PRESSED_KEY == keyCodes.DOWN)
		{
			goToNextSlide();
			event.preventDefault();
		}

	}

	/*
	*   When user scrolls with the mouse, we have to change slides
	* */
	function onMouseWheel(event)
	{
		//Normalize event wheel delta
		var delta = event.originalEvent.wheelDelta / 30 || -event.originalEvent.detail;

		//If the user scrolled up, it goes to previous slide, otherwise - to next slide
		if(delta < -1)
		{
			goToNextSlide();
		}
		else if(delta > 1)
		{
			goToPrevSlide();
		}

		event.preventDefault();
	}

	/*
	*   If there's a previous slide, slide to it
	* */
	function goToPrevSlide()
	{
		if($currentSlide.prev().length)
		{
			goToSlide($currentSlide.prev());
		}
	}

	/*
	*   If there's a next slide, slide to it
	* */
	function goToNextSlide()
	{
		if($currentSlide.next().length)
		{
			goToSlide($currentSlide.next());
		}
	}

	/*
	*   Actual transition between slides
	* */
	function goToSlide($slide)
	{
		//If the slides are not changing and there's such a slide
		if(!isAnimating && $slide.length)
		{
           
			//setting animating flag to true
			isAnimating = true;
			$currentSlide = $slide;
      
      // Get the circle to animate
      var circle = circles.get($currentSlide.index());

			//Sliding to current slide
			TweenLite.to($slidesContainer, 1, {scrollTo: {y: pageHeight * $currentSlide.index() }, onComplete: onSlideChangeEnd, onCompleteScope: this, onCompleteParams: [circle]});

			//Animating menu items
			TweenLite.to($navButtons.filter(".active"), 0.5, {className: "-=active"});

			TweenLite.to($navButtons.filter("[href=#" + $currentSlide.attr("id") + "]"), 0.5, {className: "+=active"});

		}
	}

	/*
	*   Once the sliding is finished, we need to restore "isAnimating" flag.
	*   You can also do other things in this function, such as changing page title
	* */
	function onSlideChangeEnd(target)
	{
    
    playAnimation(target);
    
		isAnimating = false;
	}

	/*
	*   When user resize it's browser we need to know the new height, so we can properly align the current slide
	* */
	function onResize(event)
	{

		//This will give us the new height of the window
		var newPageHeight = $window.innerHeight();

		/*
		*   If the new height is different from the old height ( the browser is resized vertically ), the slides are resized
		* */
		if(pageHeight !== newPageHeight)
		{
			pageHeight = newPageHeight;

			//This can be done via CSS only, but fails into some old browsers, so I prefer to set height via JS
			TweenLite.set([$slidesContainer, $slides], {height: pageHeight + "px"});

			//The current slide should be always on the top
			TweenLite.set($slidesContainer, {scrollTo: {y: pageHeight * $currentSlide.index() }});
		}

	}