var imageCount = 0;
var imageWidth = 700;
var increment = 35;
var curPos = 0;
var curImg = 0;
var slideInterval;
var fadeInterval;
var out = true;
var textOpacity = 1;
var currentText = 0;
var textOptions;

function getImageCount() {
	var full = new Image();
	
	full.src = 'images/events.jpg';
	
	imageCount = full.width / imageWidth;
}

function getTextOptions() {
	textOptions = document.getElementById("information").children;
	document.getElementById("eventInfo").innerHTML = textOptions[0].innerHTML;
}

function moveImage(back) {
	var image = document.getElementById("slider");
	
	if (back) {
		curPos -= increment;
	} else {
		curPos += increment;
	}
	image.style.backgroundPosition = curPos + "px 0px";
	
	if (curPos % imageWidth == 0) {
		clearInterval(slideInterval)
		slideInterval = null;
	}
		
}

function fadeText() {
	var paragraph = document.getElementById("eventInfo");
	
	if (out) {
		textOpacity -= 0.1;
	} else {
		textOpacity += 0.1
	}
	
	paragraph.style.opacity = textOpacity;
	paragraph.style.filter = "alpha(opacity=" + textOpacity * 100 + ")";
	
	if (textOpacity <= -0.3) {
		paragraph.innerHTML = textOptions[currentText].innerHTML;
		out = false;
	}
	
	if (textOpacity > 1) {
		clearInterval(fadeInterval);
		fadeInterval = null;
		out = true;
	}
}

function startAnimation(back) {
	if (!slideInterval && !fadeInterval) {
		slideInterval = setInterval(function() {moveImage(back);}, 20);
		fadeInterval = setInterval(fadeText, 20);
	
			if (back) {
				currentText++;
				if (currentText == textOptions.length)
					currentText = 0;	
				curImg++;
				if (curImg == imageCount - 1)
					document.getElementById("nextButton").style.visibility = "hidden";
				document.getElementById("backButton").style.visibility = "visible";
			} else {
				currentText--;
				if (currentText < 0)
					currentText = textOptions.length - 1;
				curImg--;
				if (curImg == 0)
					document.getElementById("backButton").style.visibility = "hidden";				
				document.getElementById("nextButton").style.visibility = "visible";
			}
		}
}