/* 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 = document.id(this.options.container);
    this.enters = this.leaves = 0;
    
    /* fix max */
    if(this.options.max === 0) 
    { 
      var ss = this.container.getScrollSize();
      this.options.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((this.options.min===false || xy >= this.options.min) && (this.options.max===false || xy <= this.options.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));
  }
});