var currentRow = 10;
var n = 0;
function next(fx){
	if(currentRow < $('inner').getHeight() - $('selector').getHeight()){
		fx.cancel();
		n = currentRow + 50;
		fx.start("margin-top", -n);
		currentRow = n;
	}
}
function prev(fx){
	if(currentRow >= 60){
		fx.cancel();
		n = currentRow - 50;
		fx.start("margin-top", -n);
		currentRow = n;
	}
}

window.addEvent('domready', function(){
	var el = $('inner');
	if(el.getHeight() < 277){
		$('nav').setStyle('opacity', 0);
	}else{
		var fx = new Fx.Tween(el, {duration: 500, transition: Fx.Transitions.Sine.easeOut});
		$('next').addEvent('click', function(ev){ev = new Event(ev).stop(); next(fx);});
		$('prev').addEvent('click', function(ev){ev = new Event(ev).stop(); prev(fx);});
		$('selector').addEvent('mousewheel', function(ev){
			ev = new Event(ev).stop();
			if(ev.wheel == 1){
				prev(fx);
			}else{
				next(fx);
			}
		});
	}
});