var ScrollSidebar = new Class({
  
  Implements: [Options],
  
  options: {
    offsets: { x:0, y:0 },
    mode: 'vertical',
    positionVertical: 'top',
    positionHorizontal: 'right',
    speed: 400
  },
  
  initialize: function(menu,options) {
    /* initial options */
    this.setOptions(options);
    this.menu = $(menu);
    this.move = this.options.mode == 'vertical' ? 'y' : 'x';
    this.property = this.move == 'y' ? 'positionVertical' : 'positionHorizontal';
    /* ensure a few things */
    var css = { position: 'absolute', display:'block' };
    css[this.options.positionVertical] = this.options.offsets.y;
    css[this.options.positionHorizontal] = this.options.offsets.x;
    this.menu.setStyles(css).set('tween',{ duration: this.options.speed });
    /* start listening */
    this.startListeners();
  },
  
  startListeners: function() {
    var action = function() {
	     this.setPosition($(document.body).getScroll()[this.move] + this.options.offsets[this.move]-380);
    }.bind(this);
    window.addEvent('scroll',action);
    window.addEvent('load',action);
  },
  
  setPosition: function(move) {
	move=(move>0) ? move : 0;
		this.menu.tween(this.options[this.property],move);
    return this;
  }
});