function Range() {
    this._value = 0;
    this._minimum = 0;
    this._maximum = 100;
    this._extent = 0;
    
    this._isChanging = false;
}

Range.prototype.setValue = function (value) {
    value = parseInt(value);
    if (isNaN(value)) return;
    if (this._value != value) {
        if (value + this._extent > this._maximum)
            this._value = this._maximum - this._extent;
        else if (value < this._minimum)
            this._value = this._minimum;
        else
            this._value = value;
        if (!this._isChanging && typeof this.onchange == "function")
             this.onchange();
    }
};

Range.prototype.getValue = function () {
    return this._value;
};

Range.prototype.setExtent = function (extent) {
    if (this._extent != extent) {
        if (extent < 0)
            this._extent = 0;
        else if (this._value + extent > this._maximum)
            this._extent = this._maximum - this._value;
        else
            this._extent = extent;
        if (!this._isChanging && typeof this.onchange == "function")
            this.onchange();
    }
};

Range.prototype.getExtent = function () {
    return this._extent;
};

Range.prototype.setMinimum = function (minimum) {
    if (this._minimum != minimum) {
        var oldIsChanging = this._isChanging;
        this._isChanging = true;

        this._minimum = minimum;
        
        if (minimum > this._value)
            this.setValue(minimum);
        if (minimum > this._maximum) {
            this._extent = 0;
            this.setMaximum(minimum);
            this.setValue(minimum)
        }
        if (minimum + this._extent > this._maximum)
            this._extent = this._maximum - this._minimum;

        this._isChanging = oldIsChanging;
        if (!this._isChanging && typeof this.onchange == "function")
            this.onchange();
    }
};

Range.prototype.getMinimum = function () {
    return this._minimum;
};

Range.prototype.setMaximum = function (maximum) {
    if (this._maximum != maximum) {
        var oldIsChanging = this._isChanging;
        this._isChanging = true;

        this._maximum = maximum;        
        
        if (maximum < this._value)
            this.setValue(maximum - this._extent);
        if (maximum < this._minimum) {
            this._extent = 0;
            this.setMinimum(maximum);
            this.setValue(this._maximum);
        }       
        if (maximum < this._minimum + this._extent)
            this._extent = this._maximum - this._minimum;
        if (maximum < this._value + this._extent)
            this._extent = this._maximum - this._value;
        
        this._isChanging = oldIsChanging;
        if (!this._isChanging && typeof this.onchange == "function")
            this.onchange();
    }
};

Range.prototype.getMaximum = function () {
    return this._maximum;
};