// Fade interval in milliseconds
// Make this larger if you experience performance issues
Fadomatic.INTERVAL_MILLIS=50;

// Creates a fader
// element - The element to fade
// rate - The speed to fade at, from 0.0 to 100.0
// initialOpacity (optional, default 100) - element's starting opacity, 0 to 100
// minOpacity (optional, default 0) - element's minimum opacity, 0 to 100
// maxOpacity (optional, default 0) - element's minimum opacity, 0 to 100
function Fadomatic(idElement, rate, initialOpacity, minOpacity, maxOpacity){
  this._element=d.getElementById(idElement);
  this._intervalId=null;
  this._rate=rate;
  this._isFadeOut=true;

  // Set initial opacity and bounds
  // NB use 99 instead of 100 to avoid flicker at start of fade
  this._minOpacity=0;
  this._maxOpacity=99;
  this._opacity=99;

  if(typeof minOpacity!='undefined'){
   if(minOpacity<0) this._minOpacity=0;
   else if(minOpacity>99) this._minOpacity=99;
        else this._minOpacity=minOpacity;
  }

  if(typeof maxOpacity!='undefined'){
   if(maxOpacity<0) this._maxOpacity=0;
   else if(maxOpacity>99) this._maxOpacity=99;
        else this._maxOpacity=maxOpacity;
				
   if(this._maxOpacity<this._minOpacity) this._maxOpacity=this._minOpacity;
  }
  
  if(typeof initialOpacity!='undefined'){
   if (initialOpacity>this._maxOpacity) this._opacity=this._maxOpacity;
   else if(initialOpacity<this._minOpacity) this._opacity=this._minOpacity;
        else this._opacity=initialOpacity;
  }

  // See if we're using W3C opacity, MSIE filter, or just
  // toggling visiblity
  if(typeof this._element.style.opacity!='undefined') this._updateOpacity=this._updateOpacityW3c;
  else{
	 if(typeof this._element.style.filter!='undefined'){
    // If there's not an alpha filter on the element already,
    // add one
    if(this._element.style.filter.indexOf("alpha")==-1){
     // Attempt to preserve existing filters
     var existingFilters="";
     if(this._element.style.filter) existingFilters=this._element.style.filter+" ";
     this._element.style.filter=existingFilters+"alpha(opacity="+this._opacity+")";
    }
    this._updateOpacity=this._updateOpacityMSIE;
   }
	 else this._updateOpacity=this._updateVisibility;
  }
  this._updateOpacity();
}

// Initiates a fade out
Fadomatic.prototype.fadeOut=function(){
 this._isFadeOut=true;
 this._beginFade();
}

// Initiates a fade in
Fadomatic.prototype.fadeIn=function(){
 this._isFadeOut=false;
 this._beginFade();
}

// Makes the element completely opaque, stops any fade in progress
Fadomatic.prototype.show=function(){
 this.haltFade();
 this._opacity=this._maxOpacity;
 this._updateOpacity();
}

// Makes the element completely transparent, stops any fade in progress
Fadomatic.prototype.hide=function(){
 this.haltFade();
 this._opacity=0;
 this._updateOpacity();
}

// Halts any fade in progress
Fadomatic.prototype.haltFade=function(){
 clearInterval(this._intervalId);
}

// Resumes a fade where it was halted
Fadomatic.prototype.resumeFade=function(){
 this._beginFade();
}

// Pseudo-private members
Fadomatic.prototype._beginFade=function(){
 this.haltFade();
 var objref=this;
 this._intervalId=setInterval(function(){objref._tickFade();},Fadomatic.INTERVAL_MILLIS);
}

Fadomatic.prototype._tickFade=function(){
 if(this._isFadeOut){
  this._opacity-=this._rate;
  if(this._opacity<this._minOpacity){
   this._opacity=this._minOpacity;
   this.haltFade();
  }
 }
 else{
  this._opacity+=this._rate;
  if(this._opacity>this._maxOpacity){
   this._opacity=this._maxOpacity;
   this.haltFade();
  }
 }
 this._updateOpacity();
}

Fadomatic.prototype._updateVisibility=function(){
 if(this._opacity>0) this._element.style.visibility='visible';
 else this._element.style.visibility='hidden';
}

Fadomatic.prototype._updateOpacityW3c=function(){
 this._element.style.opacity=this._opacity/100;
 this._updateVisibility();
}

Fadomatic.prototype._updateOpacityMSIE=function(){
 this._element.filters.alpha.opacity=this._opacity;
 this._updateVisibility();
}

Fadomatic.prototype._updateOpacity=null;