var interval = 8000;
var visibleClassName = '';
var hiddenClassName = 'hidden';
var intervalId = '';
var mainDirection = 'right';

function changeElement (direction) {
	var dir;
	var children = document.getElementById('container').getElementsByTagName('li');
	var count = children.length;
	
	switch (direction) {
		case 'left':
			dir = -1;
			break;
		case 'right':
			dir = 1;
			break;
		case 'random':
			var key = Math.floor(count * Math.random())
			children[key].className = '';
			autoRotate(true, mainDirection);
			return true;
			break;
		default:
			return false;
			break;
	}
		
	for (var i = 0; i < count; i++) {		
		if (children[i].className == '') {
			switchElementKey = i + dir;
			children[i].className = hiddenClassName;
			if (switchElementKey < 0) {
				switchElementKey = count - 1;
			} else if (switchElementKey >= count) {
				switchElementKey = 0
			} 
			children[switchElementKey].className = visibleClassName;
			break;
		}
	} 
}

function autoRotate (modifier, direction) {
	
	if (modifier == true) {
		intervalId = setInterval ( "changeElement('"+direction+"')", interval );
	} else if (modifier == false ) {
		if (intervalId != '') {
			clearInterval(intervalId);
			intervalId = '';
		} 
	}	
}