/* scroll spy plugin / class */
	var ScrollSpy = new Class({
		
		/* implements */
		Implements: [Options,Events],
	
		/* options */
		options: {
			min: 0,
			mode: 'vertical',
			max: 0,
			container: window,
			onEnter: $empty,
			onLeave: $empty,
			onTick: $empty
		},
		
		/* initialization */
		initialize: function(options) {
			/* set options */
			this.setOptions(options);
			this.container = $(this.options.container);
			this.enters = this.leaves = 0;
			this.max = this.options.max;
			
			/* fix max */
			if(this.max == 0) 
			{ 
				var ss = this.container.getScrollSize();
				this.max = this.options.mode == 'vertical' ? ss.y : ss.x;
			}
			/* make it happen */
			this.addListener();
		},
		
		/* a method that does whatever you want */
		addListener: function() {
			/* state trackers */
			this.inside = false;
			this.container.addEvent('scroll',function() {
				/* if it has reached the level */
				var position = this.container.getScroll();
				var xy = this.options.mode == 'vertical' ? position.y : position.x;
				/* if we reach the minimum and are still below the max... */
				if(xy >= this.options.min && xy <= this.max) {
						/* trigger Enter event if necessary */
						if(!this.inside) {
							/* record as inside */
							this.inside = true;
							this.enters++;
							/* fire enter event */
							this.fireEvent('enter',[position,this.enters]);
						}
						/* trigger the "tick", always */
						this.fireEvent('tick',[position,this.inside,this.enters,this.leaves]);
				}
				else {
					/* trigger leave */
					if(this.inside) 
					{
						this.inside = false;
						this.leaves++;
						this.fireEvent('leave',[position,this.leaves]);
					}
				}
			}.bind(this));
		}
	});