// 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 minimum 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') {

// If there's not an alpha filter on the element already,
// add one
if (element.style.filter.indexOf("alpha") == -1) {

// 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;