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/*

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

var svgNS = "http://www.w3.org/2000/svg";
var xlinkNS = "http://www.w3.org/1999/xlink";

function ScrollBar(contentId, 
                   steps,
                   scrollBarX,
                   scrollBarY,
                   scrollBarHeight,
                   scrolledHeight,
                   arrowWidth,
                   upArrowId, downArrowId, 
                   cursorId, cursorHeight){
    this.content = document.getElementById(contentId);
    this.steps = steps;
    this.curStep = 0;
    this.scrollBarHeight = scrollBarHeight;
    this.scrolledHeight = scrolledHeight;
    this.arrowWidth = arrowWidth;
    this.cursorHeight = cursorHeight;

    //
    // First, add the elements which make up the scroll bar
    //
    var insertAt = this.content.getParentNode().getParentNode();

    //
    // Add the up arrow
    //
    var upArrow = document.createElementNS(svgNS, 'use');
    upArrow.setAttributeNS(xlinkNS, 'href', upArrowId);
    upArrow.setAttributeNS(null, 'x', scrollBarX);
    upArrow.setAttributeNS(null, 'y', scrollBarY);
    insertAt.appendChild(upArrow);
        
    //
    // Add the down arrow
    //
    var downArrow = document.createElementNS(svgNS, 'use');
    downArrow.setAttributeNS(xlinkNS, 'href', downArrowId);
    downArrow.setAttributeNS(null, 'x', scrollBarX);
    downArrow.setAttributeNS(null, 'y', scrollBarY + scrollBarHeight - arrowWidth);
    insertAt.appendChild(downArrow);

    //
    // Add the cursor
    //
    var cursor = document.createElementNS(svgNS, 'use');
    cursor.setAttributeNS(xlinkNS, 'href', cursorId);
    cursor.setAttributeNS(null, 'x', scrollBarX);
    cursor.setAttributeNS(null, 'y', scrollBarY + arrowWidth);

    this.cursor = document.createElementNS(svgNS, 'g');
    this.cursor.appendChild(cursor);
    insertAt.appendChild(this.cursor);

    //
    // Now, add event handling to scroll the content 
    //

    // Scrolling down means moving the cursor up and 
    // content down (i.e., towards the positive side
    // of the Y axis).          


    this.scrollToStep = function(newStep){
        //
        // Compute new position for cursor
        //
        var cursorPos = newStep*((this.scrollBarHeight - 2*this.arrowWidth - this.cursorHeight) / this.steps);
        this.cursor.setAttributeNS(null, "transform", "translate(0," + cursorPos + ")");
       
        //
        // Compute new content position
        //
        var contentPos = - newStep*(this.scrolledHeight / this.steps);
        this.content.setAttributeNS(null, "transform", "translate(0," + contentPos + ")");

        this.curStep = newStep;
    }


    // Scrolling up means moving the cursor down and
    // the content up (i.e., towards the negative side
    // of the Y axis).
    this.handleScrollUp = function(evt) {
        if (this.curStep < (this.steps - 1)){
            this.scrollToStep(this.curStep + 1);
        }
    }

    this.handleScrollDown = function(evt) {
        if (this.curStep > 0){
            this.scrollToStep(this.curStep - 1);
        }
    }

    this.getHandleScrollDownFunction = function() {
        var thisObject = this;
        return function(evt) { thisObject.handleScrollDown(evt); }
    }

    this.getHandleScrollUpFunction = function() {
        var thisObject = this;
        return function(evt) { thisObject.handleScrollUp(evt); }
    }

    upArrow.addEventListener('click', this.getHandleScrollDownFunction(), false);
    downArrow.addEventListener('click', this.getHandleScrollUpFunction(), false);

}