/**
 * back-to-top: unobtrusive global 'back to top' link using mootools 1.2.x
 * 
 * copyright (c) 2007-2009 by gonchuki - http://blog.gonchuki.com
 *                   and Nicolas Sanguinetti - http://nicolassanguinetti.info
 * 
 * version:	1.2
 * released: November 11, 2007
 * last modified: February 27, 2009
 * 
 * This work is licensed under a Creative Commons Attribution-Share Alike 3.0 License.
 *   http://creativecommons.org/licenses/by-sa/3.0/
 */

// hide the effect from IE6, better not having it at all than being choppy.
if (!Browser.Engine.trident4) {
  // element added onload for IE to avoid the "operation aborted" bug. not yet verified for IE8 as it's still on beta as of this modification.
  window.addEvent((Browser.Engine.trident ? 'load' : 'domready'), function(){
    var target_opacity = 0.64;
    new Element('span', {
      'id': 'back-to-top', 
      'styles': {
        opacity: target_opacity,
        display: 'none',
        position: 'fixed',
        bottom: 0,
        right: 0,
        cursor: 'pointer'
      },
      'text': 'back to top',
      'tween': {
        duration: 200,
        onComplete: function(el) { if (el.get('opacity') == 0) el.setStyle('display', 'none')}
      },
      'events': {'click': function() {
        if (window.location.hash) { window.location.hash = '#top'; } 
        else { window.scrollTo(0, 0); }
      }}
    }).inject(document.body);
    
    window.addEvent('scroll', function() {
      var visible = window.getScroll().y > (window.getSize().y * 0.8);
      if (visible == arguments.callee.prototype.last_state) return;
      
      // fade if supported
      if (Fx && Fx.Tween) {
        if (visible) $('back-to-top').fade('hide').setStyle('display', 'inline').fade(target_opacity);
        else $('back-to-top').fade('out');
      } else {
        $('back-to-top').setStyle('display', (visible ? 'inline' : 'none'));
      }
      
      arguments.callee.prototype.last_state = visible
    });
  });
}