/**
 * ImageSwitcher
 *  画像の名前を*_off.jpgとすれば、自動で*_on.jpgを読み込み、マウスオーバー設定を行う。a要素直下のimgに限る。
 *  require: prototype.js
 */
ImageSwitcher = {
  onImagePostfix: '_on',
  offImagePostfix: '_off',
  extension: '(jpe?g|png|gif)',
  load: function(){
    var offImagePostfix = this.offImagePostfix;
    var onImagePostfix  = this.onImagePostfix;
    var extension       = this.extension;
    
    if (typeof(Prototype) == 'undefined'){
      return;
    }
    Event.observe(window, 'load', function(){
      var images = [];
      var reg = new RegExp('^(.*)' + offImagePostfix + '\.' + extension, 'i');
      var imgTags = $A(document.getElementsByTagName('img'));
      imgTags.each(function(img){
        if (img.parentNode.tagName == 'A' && reg.match(img.src)){
          images.push({
            base: img,
            baseSrc: img.src + "", // new string
            onImage: function(){ var n = new Image(); n.src = RegExp.$1 + onImagePostfix + '.' + RegExp.$2; return n;}()
          });
        }
      });
      $A(images).each(function(p){
        var base = p.base;
        base.onmouseover = function(){
          base.src = p.onImage.src;
        }
        base.onmouseout = function(){
          base.src = p.baseSrc;
        }
      });
    });
  }
};
ImageSwitcher.load();