/*****
Very nifty script from http://chimpen.com/fadomatic/

Thanks very much for making this public.

From that page:

To use it, first construct a new Fadomatic instance, passing in the element you want to change the opacity of, and the rate of fading you want.

eg: var fader = new Fadomatic(someElement, 5);

The rate parameter is a floating point number between 0 and 100. The fade effects are applied 20 times a second, so setting the rate to 5 means a complete fade from transparent to opaque will take 1 second.

An optional third parameter specifies the initial opacity of the element, where 0 is transparent, and 100 is opaque. The default value is 100.

eg: new Fadomatic(someElement, 5, 0) will make the element transparent initially.

Optional fourth and fifth parameters allow you to specify the minimum and maximum opacities to use, again from 0 to 100.

eg: new Fadomatic(someElement, 5, 0, 40, 60) will constrain fades to the range 40-60%. Note that if you set the minumum to a non-zero value, the element will always remain opaque in browsers that don't support variable opacity.

Note that it's up to you to take care of sizing and positioning the elements you want to fade, via markup, script or whatever. Fadomatic only takes care of fading them in and out.

methods

There are six public methods on the Fadomatic object, which are fairly self-explanatory:

fadeOut() - Initiates a fade toward transparency.

fadeIn() - Initiates a fade toward opacity.

haltFade() - Stops the current fade transition.

resumeFade() - Continues the current fade transition.

show() - Sets the element's opacity to the maximum value.

hide() - Makes the element transparent.

*****/


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

// Creates a fader
// element - The element to fade
// speed - 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 maximum opacity, 0 to 100
function Fadomatic (element, rate, initialOpacity, minOpacity, maxOpacity) {
  this._element = element;
  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 element.style.opacity != 'undefined') {

    this._updateOpacity = this._updateOpacityW3c;

  } else if(typeof element.style.filter != 'undefined') {

    // Attempt to preserve existing filters
    var existingFilters="";
    if (element.style.filter) {
      existingFilters = element.style.filter+" ";
    }
    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;