var TractBehavior = Class.create();

TractBehavior.Apply = function() {

	var page = 1;
	var maxpage = 8;
	
	var lnkNext = $('tract').down('.next');
	lnkNext.onclick = function() {
		if (page == maxpage) {
			page = 1;
	    }
		else {
			page++;
		}
		
		// Insert new pic
		var ePic = $('tract').down('.pic');
		Element.update(ePic, '<img src="images/tract/tract'+page+'.jpg" />');
		
		checkPrevNext();

	};
	
	var lnkPrev = $('tract').down('.prev');
	if (page == 1) {
		Element.addClassName(lnkPrev, 'hidden');
	}
	lnkPrev.onclick = function() {
		if (page == 1) {
			page = maxpage;
	    }
		else {
			page--;
		}
		
		// Insert new pic
		var ePic = $('tract').down('.pic');
		Element.update(ePic, '<img src="images/tract/tract'+page+'.jpg" />');
		
		checkPrevNext();

	};
	
	function checkPrevNext() {
		// Check if need next link
		var lnkNext = $('tract').down('.next');
		if (page == maxpage) {
			Element.addClassName(lnkNext, 'hidden');
		}
		else {
			Element.removeClassName(lnkNext, 'hidden');
		}
		
		// Check if need prev link
		var lnkPrev = $('tract').down('.prev');
		if (page == 1) {
			Element.addClassName(lnkPrev, 'hidden');
		}
		else {
			Element.removeClassName(lnkPrev, 'hidden');
		}
	}
	
};