/**

 * Copyright (c) 2009-2010 Symbian Foundation and/or its subsidiary(-ies).

 * All rights reserved.

 * This component and the accompanying materials are made available

 * under the terms of the License "Eclipse Public License v1.0"

 * which accompanies this distribution, and is available

 * at the URL "http://www.eclipse.org/legal/epl-v10.html".

 *

 * Initial Contributors:

 * Contributors:

 */

///////////////////////////////////////////////////////////////////////////////

// The Scrollbar class is an implementation of a user interface element that

// indicates the current viewport position in a document.

// Constructor.

function Scrollbar(parentElement) {

    uiLogger.debug("Scrollbar(" + parentElement + ")");

    // get the parent element

    this.parentElement = parentElement;

    // create the root element

    this.rootElement = document.createElement("div");

    this.rootElement.className = "Scrollbar";

    this.rootElement.style.visibility = "hidden";

    // create the scrollbar

    // the scrollbar consists of a root element with six children

    // (three track elements and three thumb elements)

    // track

    this.trackTopElement = document.createElement("div");

    this.trackTopElement.className = "ScrollbarTrackTop";

    this.trackMiddleElement = document.createElement("div");

    this.trackMiddleElement.className = "ScrollbarTrackMiddle";

    this.trackBottomElement = document.createElement("div");

    this.trackBottomElement.className = "ScrollbarTrackBottom";

    // thumb

    this.thumbTopElement = document.createElement("div");

    this.thumbTopElement.className = "ScrollbarThumbTop";

    this.thumbMiddleElement = document.createElement("div");

    this.thumbMiddleElement.className = "ScrollbarThumbMiddle";

    this.thumbBottomElement = document.createElement("div");

    this.thumbBottomElement.className = "ScrollbarThumbBottom";

    // assemble and attach the scrollbar

    this.rootElement.appendChild(this.trackTopElement);

    this.rootElement.appendChild(this.trackMiddleElement);

    this.rootElement.appendChild(this.trackBottomElement);

    this.rootElement.appendChild(this.thumbTopElement);

    this.rootElement.appendChild(this.thumbMiddleElement);

    this.rootElement.appendChild(this.thumbBottomElement);

    this.parentElement.appendChild(this.rootElement);

    // bring the scrollbar up to date

    this.update(0, 100, 100);

}

// Parent element for the scrollbar.

Scrollbar.prototype.parentElement = null;

// Root HTML element in the scrollbar.

Scrollbar.prototype.rootElement = null;

// Scrollbar track top element.

Scrollbar.prototype.trackTopElement = null;

// Scrollbar track middle element.

Scrollbar.prototype.trackMiddleElement = null;

// Scrollbar track bottom element.

Scrollbar.prototype.trackBottomElement = null;

// Scrollbar thumb top element.

Scrollbar.prototype.thumbTopElement = null;

// Scrollbar thumb middle element.

Scrollbar.prototype.thumbMiddleElement = null;

// Scrollbar thumb bottom element.

Scrollbar.prototype.thumbBottomElement = null;

// Is the scrollbar needed?

Scrollbar.prototype.scrollbarNeeded = false;

// Updates the scrollbar.

Scrollbar.prototype.update = function(scrollY, viewportHeight, documentHeight) {

    // figure out current heights

    var scrollbarHeight = this.rootElement.clientHeight;

    var trackTopHeight = this.trackTopElement.clientHeight;

    var trackBottomHeight = this.trackBottomElement.clientHeight;

    var thumbTopHeight = this.thumbTopElement.clientHeight;

    var thumbBottomHeight = this.thumbBottomElement.clientHeight;

    // scrollable height is the larger of document and viewport heights

    var scrollableHeight = documentHeight;

    var scrollbarNeeded = true;

    if (viewportHeight >= documentHeight) {

        scrollableHeight = viewportHeight;

        scrollbarNeeded = false;

    }

    // show or hide scrollbar?

    if (scrollbarNeeded != this.scrollbarNeeded) {

        this.scrollbarNeeded = scrollbarNeeded;

        this.rootElement.style.visibility = scrollbarNeeded ? "visible" : "hidden";

    }

    // calculate thumb top position...

    var thumbTopPct = scrollY / scrollableHeight;

    var thumbTop = scrollbarHeight * thumbTopPct;

    // ...and bottom position...

    var thumbBottomPct = (scrollY + viewportHeight) / scrollableHeight;

    var thumbBottom = scrollbarHeight * thumbBottomPct;

    // ...and thumb height

    var thumbHeight = thumbBottom - thumbTop;

    // ensure that the thumb is not too small

    var thumbMinHeight = thumbTopHeight + thumbBottomHeight;

    if (thumbHeight < thumbMinHeight) {

        var underflow = thumbMinHeight - thumbHeight;

        // adjust thumb top pos assuming a shorter scrollbar track

        var thumbMid = (scrollbarHeight - underflow) * ((thumbTopPct + thumbBottomPct) / 2) + (underflow / 2);

        thumbTop = thumbMid - (thumbMinHeight / 2);

        thumbBottom = thumbTop + thumbMinHeight;

        thumbHeight = thumbBottom - thumbTop;

    }

    // position and size track element (add 1 to the middle section height for rounding errors)

    this.trackTopElement.style.top = "0px";

    this.trackMiddleElement.style.top = Math.round(trackTopHeight) + "px";

    this.trackMiddleElement.style.height = Math.round(scrollbarHeight - trackTopHeight - trackBottomHeight + 1) + "px";

    this.trackBottomElement.style.top = Math.round(scrollbarHeight - trackTopHeight) + "px";

    // position and size thumb element (add 1 to the middle section height for rounding errors)

    this.thumbTopElement.style.top = Math.round(thumbTop) + "px";

    this.thumbMiddleElement.style.top = Math.round(thumbTop + thumbTopHeight) + "px";

    this.thumbMiddleElement.style.height = Math.round(thumbHeight - thumbTopHeight - thumbBottomHeight + 1) + "px";

    this.thumbBottomElement.style.top = Math.round(thumbBottom - thumbBottomHeight) + "px";

};