var nextPrev = {
	screens: new Array(),
	current: 0,
	nextBtn: null,
	prevBtn: null,
	done: null,
	
	init: function(screensLength, nextBtnID, prevBtnID, doneID){
		if(!screensLength || !nextBtnID || !prevBtnID || !doneID){
			alert('nextPrev.init error: args missing');
			return
		}
		nextPrev.screens = new Array();
		for(var i=0; i<screensLength; i++){
			nextPrev.screens[i] = $('next_prev_'+i);
		}
		nextPrev.current = 0;
		nextPrev.nextBtn = $(nextBtnID);
		nextPrev.prevBtn = $(prevBtnID);
		nextPrev.done = $(doneID);
		
		nextPrev.nextBtn.href="javascript:nextPrev.next()";
		nextPrev.prevBtn.href="javascript:nextPrev.previous()";
	},
	
	next: function(){
		if(!nextPrev.check()){
			alert2('Please make your choice.');
			return;
		}
		nextPrev.current++;
		nextPrev.hide();
		if(nextPrev.current < nextPrev.screens.length){
			nextPrev.screens[nextPrev.current].style.display = 'inline';
		}
	},
	
	previous: function(){
		nextPrev.current--;
		nextPrev.hide();
		if(nextPrev.current >= 0){
			nextPrev.screens[nextPrev.current].style.display = 'inline';
		}
	},
	
	check: function(){
		var choices = nextPrev.screens[nextPrev.current].select('input[type="radio"]');
		for(var i=0; i<choices.length; i++){
			if(choices[i].checked){
				return true;
			}
		} 
		return false;
	},
	
	hide: function(){
		for(var i = 0; i<nextPrev.screens.length; i++){
			nextPrev.screens[i].style.display = 'none';
		}
		
		nextPrev.nextBtn.style.display = 'inline';
		nextPrev.prevBtn.style.display = 'inline';
		
		if(nextPrev.current == nextPrev.screens.length){
			nextPrev.nextBtn.style.display = 'none';
			nextPrev.done.style.display = 'inline';
		}
		else{
			nextPrev.done.style.display = 'none';
		}
		
		if(nextPrev.current == 0){
			nextPrev.prevBtn.style.display = 'none';
		}
	}
};