$(document).ready(function() { //when the document is ready...


	//save selectors as variables to increase performance
	var $window = $(window);
	var $firstBG = $('#intro');
	var $secondBG = $('#connect');
	var $thirdBG = $('#work');
	var $fourthBG = $('#process');
	var $fifthBG = $('#contact');
	var $sixthBG = $('#location');
	var trainers = $("#intro .bg");
	var trainers1 = $("#connect .bg");
	var trainers3 = $("#work .bg");
	var trainers4 = $("#process .bg");
	
	var windowHeight = $window.height(); //get the height of the window
	
	
	//apply the class "inview" to a section that is in the viewport
	$('#intro, #connect, #work, #process, #contact, #location').bind('inview', function (event, visible) {
			if (visible == true) {
			$(this).addClass("inview");
			} else {
			$(this).removeClass("inview");
			}
		});
	
	//loader
	
	
	//function that places the toghead at top of the window
	function RepositionNav(){
		var windowHeight = $window.height(); //get the height of the window
		var navHeight = $('#nav').height() / 2;
		var windowCenter = (windowHeight / 2); 
		var newtop = windowCenter - navHeight;
		$('#nav').css({"top": newtop}); //set the new top position of the navigation list
	}
	
	//function that is called for every pixel the user scrolls. Determines the position of the background
	/*arguments: 
		x = horizontal position of background
		windowHeight = height of the viewport
		pos = position of the scrollbar
		adjuster = adjust the position of the background
		inertia = how fast the background moves in relation to scrolling
	*/
	function newPos(x, windowHeight, pos, adjuster, inertia){
		return x + "% " + (-((windowHeight + pos) - adjuster) * inertia)  + "px";
	}
	
	//function to be called whenever the window is scrolled or resized
	function Move(){ 
		var pos = $window.scrollTop(); //position of the scrollbar

		//if the first section is in view...
		if($firstBG.hasClass("inview")){
			//call the newPos function and change the background position
			$firstBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 500, 0.3)}); 
			trainers.css({'backgroundPosition': newPos(50, windowHeight, pos, 1000, 0.6)});
		}
		
		//if the second section is in view...
		if($secondBG.hasClass("inview")){
			//call the newPos function and change the background position
			$secondBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 1500, 0.3)});
			//call the newPos function and change the secnond background position
			trainers1.css({'backgroundPosition': newPos(50, windowHeight, pos, 2000, 0.6)});
		}
		
		//if the third section is in view...
		if($thirdBG.hasClass("inview")){
			//call the newPos function and change the background position
			$thirdBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 2500, 0.3)});
			//call the newPos function and change the secnond background position
			//trainers3.css({'backgroundPosition': newPos(50, windowHeight, pos, 2500, 0.6)});
		}
		
		//if the fourth section is in view...
		if($fourthBG.hasClass("inview")){
			//call the newPos function and change the background position for CSS3 multiple backgrounds
			$fourthBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 3800, 0.3)});
			//call the newPos function and change the secnond background position
			//trainers4.css({'backgroundPosition': newPos(50, windowHeight, pos, 3800, 0.6)});
		}
		
		//if the fifth section is in view...
		if($fifthBG.hasClass("inview")){
			//call the newPos function and change the background position for CSS3 multiple backgrounds
			$fifthBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 4800, 0.3)});
		}
			//if the fifth section is in view...
		if($sixthBG.hasClass("inview")){
			//call the newPos function and change the background position for CSS3 multiple backgrounds
			$sixthBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 5800, 0.3)});
		}
		
		$('#pixels').html(pos); //display the number of pixels scrolled at the bottom of the page
	}
		
	RepositionNav(); //Reposition the Navigation to center it in the window when the script loads
	
	$window.resize(function(){ //if the user resizes the window...
		Move(); //move the background images in relation to the movement of the scrollbar
		RepositionNav(); //reposition the navigation list so it remains vertically central
	});		
	
	$window.bind('scroll', function(){ //when the user is scrolling...
		Move(); //move the background images in relation to the movement of the scrollbar
	});
	
});