// 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;