/*
 * Copyright 2000-2009 JetBrains s.r.o.
 *
 * Licensed 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.
 */
package com.intellij.openapi.editor.impl;

import javax.swing.*;
import javax.swing.border.Border;
import java.awt.*;

/**
 * This class is exact copy of javax.swing.ScrollPaneLayout except is does not ask component for orientation
 * and always assumes right-to-left.
 * 
 * @author max
 */
public class LeftHandScrollbarLayout extends ScrollPaneLayout {
  /**
   * The scrollpane's viewport child.
   * Default is an empty <code>JViewport</code>.
   * 
   * @see javax.swing.JScrollPane#setViewport
   */
  protected JViewport viewport;


  /**
   * The scrollpane's vertical scrollbar child.
   * Default is a <code>JScrollBar</code>.
   * 
   * @see javax.swing.JScrollPane#setVerticalScrollBar
   */
  protected JScrollBar vsb;


  /**
   * The scrollpane's horizontal scrollbar child.
   * Default is a <code>JScrollBar</code>.
   * 
   * @see javax.swing.JScrollPane#setHorizontalScrollBar
   */
  protected JScrollBar hsb;


  /**
   * The row header child.  Default is <code>null</code>.
   * 
   * @see javax.swing.JScrollPane#setRowHeader
   */
  protected JViewport rowHead;


  /**
   * The column header child.  Default is <code>null</code>.
   * 
   * @see javax.swing.JScrollPane#setColumnHeader
   */
  protected JViewport colHead;


  /**
   * The component to display in the lower left corner.
   * Default is <code>null</code>.
   * 
   * @see javax.swing.JScrollPane#setCorner
   */
  protected Component lowerLeft;


  /**
   * The component to display in the lower right corner.
   * Default is <code>null</code>.
   * 
   * @see javax.swing.JScrollPane#setCorner
   */
  protected Component lowerRight;


  /**
   * The component to display in the upper left corner.
   * Default is <code>null</code>.
   * 
   * @see javax.swing.JScrollPane#setCorner
   */
  protected Component upperLeft;


  /**
   * The component to display in the upper right corner.
   * Default is <code>null</code>.
   * 
   * @see javax.swing.JScrollPane#setCorner
   */
  protected Component upperRight;


  /**
   * The display policy for the vertical scrollbar.
   * The default is <code>JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED</code>.
   * <p/>
   * This field is obsolete, please use the <code>JScrollPane</code> field instead.
   * 
   * @see javax.swing.JScrollPane#setVerticalScrollBarPolicy
   */
  protected int vsbPolicy = VERTICAL_SCROLLBAR_AS_NEEDED;


  /**
   * The display policy for the horizontal scrollbar.
   * The default is <code>JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED</code>.
   * <p/>
   * This field is obsolete, please use the <code>JScrollPane</code> field instead.
   * 
   * @see javax.swing.JScrollPane#setHorizontalScrollBarPolicy
   */
  protected int hsbPolicy = HORIZONTAL_SCROLLBAR_AS_NEEDED;


  /**
   * This method is invoked after the ScrollPaneLayout is set as the
   * LayoutManager of a <code>JScrollPane</code>.
   * It initializes all of the internal fields that
   * are ordinarily set by <code>addLayoutComponent</code>.  For example:
   * <pre>
   * ScrollPaneLayout mySPLayout = new ScrollPanelLayout() {
   *     public void layoutContainer(Container p) {
   *         super.layoutContainer(p);
   *         // do some extra work here ...
   *     }
   * };
   * scrollpane.setLayout(mySPLayout):
   * </pre>
   */
  @Override
  public void syncWithScrollPane(JScrollPane sp) {
    viewport = sp.getViewport();
    vsb = sp.getVerticalScrollBar();
    hsb = sp.getHorizontalScrollBar();
    rowHead = sp.getRowHeader();
    colHead = sp.getColumnHeader();
    lowerLeft = sp.getCorner(LOWER_LEFT_CORNER);
    lowerRight = sp.getCorner(LOWER_RIGHT_CORNER);
    upperLeft = sp.getCorner(UPPER_LEFT_CORNER);
    upperRight = sp.getCorner(UPPER_RIGHT_CORNER);
    vsbPolicy = sp.getVerticalScrollBarPolicy();
    hsbPolicy = sp.getHorizontalScrollBarPolicy();
  }


  /**
   * Removes an existing component.  When a new component, such as
   * the left corner, or vertical scrollbar, is added, the old one,
   * if it exists, must be removed.
   * <p/>
   * This method returns <code>newC</code>. If <code>oldC</code> is
   * not equal to <code>newC</code> and is non-<code>null</code>,
   * it will be removed from its parent.
   * 
   * @param oldC the <code>Component</code> to replace
   * @param newC the <code>Component</code> to add
   * @return the <code>newC</code>
   */
  @Override
  protected Component addSingletonComponent(Component oldC, Component newC) {
    if ((oldC != null) && (oldC != newC)) {
      oldC.getParent().remove(oldC);
    }
    return newC;
  }


  /**
   * Adds the specified component to the layout. The layout is
   * identified using one of:
   * <ul>
   * <li>JScrollPane.VIEWPORT
   * <li>JScrollPane.VERTICAL_SCROLLBAR
   * <li>JScrollPane.HORIZONTAL_SCROLLBAR
   * <li>JScrollPane.ROW_HEADER
   * <li>JScrollPane.COLUMN_HEADER
   * <li>JScrollPane.LOWER_LEFT_CORNER
   * <li>JScrollPane.LOWER_RIGHT_CORNER
   * <li>JScrollPane.UPPER_LEFT_CORNER
   * <li>JScrollPane.UPPER_RIGHT_CORNER
   * </ul>
   * 
   * @param s the component identifier
   * @param c the component to be added
   * @throws IllegalArgumentException if <code>s</code> is an invalid key
   */
  @Override
  public void addLayoutComponent(String s, Component c) {
    if (s.equals(VIEWPORT)) {
      viewport = (JViewport)addSingletonComponent(viewport, c);
    }
    else if (s.equals(VERTICAL_SCROLLBAR)) {
      vsb = (JScrollBar)addSingletonComponent(vsb, c);
    }
    else if (s.equals(HORIZONTAL_SCROLLBAR)) {
      hsb = (JScrollBar)addSingletonComponent(hsb, c);
    }
    else if (s.equals(ROW_HEADER)) {
      rowHead = (JViewport)addSingletonComponent(rowHead, c);
    }
    else if (s.equals(COLUMN_HEADER)) {
      colHead = (JViewport)addSingletonComponent(colHead, c);
    }
    else if (s.equals(LOWER_LEFT_CORNER)) {
      lowerLeft = addSingletonComponent(lowerLeft, c);
    }
    else if (s.equals(LOWER_RIGHT_CORNER)) {
      lowerRight = addSingletonComponent(lowerRight, c);
    }
    else if (s.equals(UPPER_LEFT_CORNER)) {
      upperLeft = addSingletonComponent(upperLeft, c);
    }
    else if (s.equals(UPPER_RIGHT_CORNER)) {
      upperRight = addSingletonComponent(upperRight, c);
    }
    else {
      throw new IllegalArgumentException("invalid layout key " + s);
    }
  }


  /**
   * Removes the specified component from the layout.
   * 
   * @param c the component to remove
   */
  @Override
  public void removeLayoutComponent(Component c) {
    if (c == viewport) {
      viewport = null;
    }
    else if (c == vsb) {
      vsb = null;
    }
    else if (c == hsb) {
      hsb = null;
    }
    else if (c == rowHead) {
      rowHead = null;
    }
    else if (c == colHead) {
      colHead = null;
    }
    else if (c == lowerLeft) {
      lowerLeft = null;
    }
    else if (c == lowerRight) {
      lowerRight = null;
    }
    else if (c == upperLeft) {
      upperLeft = null;
    }
    else if (c == upperRight) {
      upperRight = null;
    }
  }


  /**
   * Returns the vertical scrollbar-display policy.
   * 
   * @return an integer giving the display policy
   * @see #setVerticalScrollBarPolicy
   */
  @Override
  public int getVerticalScrollBarPolicy() {
    return vsbPolicy;
  }


  /**
   * Sets the vertical scrollbar-display policy. The options
   * are:
   * <ul>
   * <li>JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED
   * <li>JScrollPane.VERTICAL_SCROLLBAR_NEVER
   * <li>JScrollPane.VERTICAL_SCROLLBAR_ALWAYS
   * </ul>
   * Note: Applications should use the <code>JScrollPane</code> version
   * of this method.  It only exists for backwards compatibility
   * with the Swing 1.0.2 (and earlier) versions of this class.
   * 
   * @param x an integer giving the display policy
   * @throws IllegalArgumentException if <code>x</code> is an invalid
   *                                  vertical scroll bar policy, as listed above
   */
  @Override
  public void setVerticalScrollBarPolicy(int x) {
    switch (x) {
      case VERTICAL_SCROLLBAR_AS_NEEDED:
      case VERTICAL_SCROLLBAR_NEVER:
      case VERTICAL_SCROLLBAR_ALWAYS:
        vsbPolicy = x;
        break;
      default:
        throw new IllegalArgumentException("invalid verticalScrollBarPolicy");
    }
  }


  /**
   * Returns the horizontal scrollbar-display policy.
   * 
   * @return an integer giving the display policy
   * @see #setHorizontalScrollBarPolicy
   */
  @Override
  public int getHorizontalScrollBarPolicy() {
    return hsbPolicy;
  }

  /**
   * Sets the horizontal scrollbar-display policy.
   * The options are:<ul>
   * <li>JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED
   * <li>JScrollPane.HOTRIZONTAL_SCROLLBAR_NEVER
   * <li>JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS
   * </ul>
   * Note: Applications should use the <code>JScrollPane</code> version
   * of this method.  It only exists for backwards compatibility
   * with the Swing 1.0.2 (and earlier) versions of this class.
   * 
   * @param x an int giving the display policy
   * @throws IllegalArgumentException if <code>x</code> is not a valid
   *                                  horizontal scrollbar policy, as listed above
   */
  @Override
  public void setHorizontalScrollBarPolicy(int x) {
    switch (x) {
      case HORIZONTAL_SCROLLBAR_AS_NEEDED:
      case HORIZONTAL_SCROLLBAR_NEVER:
      case HORIZONTAL_SCROLLBAR_ALWAYS:
        hsbPolicy = x;
        break;
      default:
        throw new IllegalArgumentException("invalid horizontalScrollBarPolicy");
    }
  }


  /**
   * Returns the <code>JViewport</code> object that displays the
   * scrollable contents.
   * 
   * @return the <code>JViewport</code> object that displays the scrollable contents
   * @see javax.swing.JScrollPane#getViewport
   */
  @Override
  public JViewport getViewport() {
    return viewport;
  }


  /**
   * Returns the <code>JScrollBar</code> object that handles horizontal scrolling.
   * 
   * @return the <code>JScrollBar</code> object that handles horizontal scrolling
   * @see javax.swing.JScrollPane#getHorizontalScrollBar
   */
  @Override
  public JScrollBar getHorizontalScrollBar() {
    return hsb;
  }

  /**
   * Returns the <code>JScrollBar</code> object that handles vertical scrolling.
   * 
   * @return the <code>JScrollBar</code> object that handles vertical scrolling
   * @see javax.swing.JScrollPane#getVerticalScrollBar
   */
  @Override
  public JScrollBar getVerticalScrollBar() {
    return vsb;
  }


  /**
   * Returns the <code>JViewport</code> object that is the row header.
   * 
   * @return the <code>JViewport</code> object that is the row header
   * @see javax.swing.JScrollPane#getRowHeader
   */
  @Override
  public JViewport getRowHeader() {
    return rowHead;
  }


  /**
   * Returns the <code>JViewport</code> object that is the column header.
   * 
   * @return the <code>JViewport</code> object that is the column header
   * @see javax.swing.JScrollPane#getColumnHeader
   */
  @Override
  public JViewport getColumnHeader() {
    return colHead;
  }


  /**
   * Returns the <code>Component</code> at the specified corner.
   * 
   * @param key the <code>String</code> specifying the corner
   * @return the <code>Component</code> at the specified corner, as defined in
   *         {@link ScrollPaneConstants}; if <code>key</code> is not one of the
   *         four corners, <code>null</code> is returned
   * @see javax.swing.JScrollPane#getCorner
   */
  @Override
  public Component getCorner(String key) {
    if (key.equals(LOWER_LEFT_CORNER)) {
      return lowerLeft;
    }
    else if (key.equals(LOWER_RIGHT_CORNER)) {
      return lowerRight;
    }
    else if (key.equals(UPPER_LEFT_CORNER)) {
      return upperLeft;
    }
    else if (key.equals(UPPER_RIGHT_CORNER)) {
      return upperRight;
    }
    else {
      return null;
    }
  }


  /**
   * The preferred size of a <code>ScrollPane</code> is the size of the insets,
   * plus the preferred size of the viewport, plus the preferred size of
   * the visible headers, plus the preferred size of the scrollbars
   * that will appear given the current view and the current
   * scrollbar displayPolicies.
   * <p>Note that the rowHeader is calculated as part of the preferred width
   * and the colHeader is calculated as part of the preferred size.
   * 
   * @param parent the <code>Container</code> that will be laid out
   * @return a <code>Dimension</code> object specifying the preferred size of the
   *         viewport and any scrollbars
   * @see ViewportLayout
   * @see LayoutManager
   */
  @Override
  public Dimension preferredLayoutSize(Container parent) {
    /* Sync the (now obsolete) policy fields with the
     * JScrollPane.
     */
    JScrollPane scrollPane = (JScrollPane)parent;
    vsbPolicy = scrollPane.getVerticalScrollBarPolicy();
    hsbPolicy = scrollPane.getHorizontalScrollBarPolicy();

    Insets insets = parent.getInsets();
    int prefWidth = insets.left + insets.right;
    int prefHeight = insets.top + insets.bottom;

    /* Note that viewport.getViewSize() is equivalent to
     * viewport.getView().getPreferredSize() modulo a null
     * view or a view whose size was explicitly set.
     */

    Dimension extentSize = null;
    Dimension viewSize = null;
    Component view = null;

    if (viewport != null) {
      extentSize = viewport.getPreferredSize();
      viewSize = viewport.getViewSize();
      view = viewport.getView();
    }

    /* If there's a viewport add its preferredSize.
     */

    if (extentSize != null) {
      prefWidth += extentSize.width;
      prefHeight += extentSize.height;
    }

    /* If there's a JScrollPane.viewportBorder, add its insets.
     */

    Border viewportBorder = scrollPane.getViewportBorder();
    if (viewportBorder != null) {
      Insets vpbInsets = viewportBorder.getBorderInsets(parent);
      prefWidth += vpbInsets.left + vpbInsets.right;
      prefHeight += vpbInsets.top + vpbInsets.bottom;
    }

    /* If a header exists and it's visible, factor its
     * preferred size in.
     */

    if ((rowHead != null) && rowHead.isVisible()) {
      prefWidth += rowHead.getPreferredSize().width;
    }

    if ((colHead != null) && colHead.isVisible()) {
      prefHeight += colHead.getPreferredSize().height;
    }

    /* If a scrollbar is going to appear, factor its preferred size in.
     * If the scrollbars policy is AS_NEEDED, this can be a little
     * tricky:
     *
     * - If the view is a Scrollable then scrollableTracksViewportWidth
     * and scrollableTracksViewportHeight can be used to effectively
     * disable scrolling (if they're true) in their respective dimensions.
     *
     * - Assuming that a scrollbar hasn't been disabled by the
     * previous constraint, we need to decide if the scrollbar is going
     * to appear to correctly compute the JScrollPanes preferred size.
     * To do this we compare the preferredSize of the viewport (the
     * extentSize) to the preferredSize of the view.  Although we're
     * not responsible for laying out the view we'll assume that the
     * JViewport will always give it its preferredSize.
     */

    if ((vsb != null) && (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {
      if (vsbPolicy == VERTICAL_SCROLLBAR_ALWAYS) {
        prefWidth += vsb.getPreferredSize().width;
      }
      else if ((viewSize != null) && (extentSize != null)) {
        boolean canScroll = true;
        if (view instanceof Scrollable) {
          canScroll = !((Scrollable)view).getScrollableTracksViewportHeight();
        }
        if (canScroll && (viewSize.height > extentSize.height)) {
          prefWidth += vsb.getPreferredSize().width;
        }
      }
    }

    if ((hsb != null) && (hsbPolicy != HORIZONTAL_SCROLLBAR_NEVER)) {
      if (hsbPolicy == HORIZONTAL_SCROLLBAR_ALWAYS) {
        prefHeight += hsb.getPreferredSize().height;
      }
      else if ((viewSize != null) && (extentSize != null)) {
        boolean canScroll = true;
        if (view instanceof Scrollable) {
          canScroll = !((Scrollable)view).getScrollableTracksViewportWidth();
        }
        if (canScroll && (viewSize.width > extentSize.width)) {
          prefHeight += hsb.getPreferredSize().height;
        }
      }
    }

    return new Dimension(prefWidth, prefHeight);
  }


  /**
   * The minimum size of a <code>ScrollPane</code> is the size of the insets
   * plus minimum size of the viewport, plus the scrollpane's
   * viewportBorder insets, plus the minimum size
   * of the visible headers, plus the minimum size of the
   * scrollbars whose displayPolicy isn't NEVER.
   * 
   * @param parent the <code>Container</code> that will be laid out
   * @return a <code>Dimension</code> object specifying the minimum size
   */
  @Override
  public Dimension minimumLayoutSize(Container parent) {
    /* Sync the (now obsolete) policy fields with the
     * JScrollPane.
     */
    JScrollPane scrollPane = (JScrollPane)parent;
    vsbPolicy = scrollPane.getVerticalScrollBarPolicy();
    hsbPolicy = scrollPane.getHorizontalScrollBarPolicy();

    Insets insets = parent.getInsets();
    int minWidth = insets.left + insets.right;
    int minHeight = insets.top + insets.bottom;

    /* If there's a viewport add its minimumSize.
     */

    if (viewport != null) {
      Dimension size = viewport.getMinimumSize();
      minWidth += size.width;
      minHeight += size.height;
    }

    /* If there's a JScrollPane.viewportBorder, add its insets.
     */

    Border viewportBorder = scrollPane.getViewportBorder();
    if (viewportBorder != null) {
      Insets vpbInsets = viewportBorder.getBorderInsets(parent);
      minWidth += vpbInsets.left + vpbInsets.right;
      minHeight += vpbInsets.top + vpbInsets.bottom;
    }

    /* If a header exists and it's visible, factor its
     * minimum size in.
     */

    if ((rowHead != null) && rowHead.isVisible()) {
      Dimension size = rowHead.getMinimumSize();
      minWidth += size.width;
      minHeight = Math.max(minHeight, size.height);
    }

    if ((colHead != null) && colHead.isVisible()) {
      Dimension size = colHead.getMinimumSize();
      minWidth = Math.max(minWidth, size.width);
      minHeight += size.height;
    }

    /* If a scrollbar might appear, factor its minimum
     * size in.
     */

    if ((vsb != null) && (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {
      Dimension size = vsb.getMinimumSize();
      minWidth += size.width;
      minHeight = Math.max(minHeight, size.height);
    }

    if ((hsb != null) && (hsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {
      Dimension size = hsb.getMinimumSize();
      minWidth = Math.max(minWidth, size.width);
      minHeight += size.height;
    }

    return new Dimension(minWidth, minHeight);
  }


  /**
   * Lays out the scrollpane. The positioning of components depends on
   * the following constraints:
   * <ul>
   * <li> The row header, if present and visible, gets its preferred
   * width and the viewport's height.
   * <p/>
   * <li> The column header, if present and visible, gets its preferred
   * height and the viewport's width.
   * <p/>
   * <li> If a vertical scrollbar is needed, i.e. if the viewport's extent
   * height is smaller than its view height or if the <code>displayPolicy</code>
   * is ALWAYS, it's treated like the row header with respect to its
   * dimensions and is made visible.
   * <p/>
   * <li> If a horizontal scrollbar is needed, it is treated like the
   * column header (see the paragraph above regarding the vertical scrollbar).
   * <p/>
   * <li> If the scrollpane has a non-<code>null</code>
   * <code>viewportBorder</code>, then space is allocated for that.
   * <p/>
   * <li> The viewport gets the space available after accounting for
   * the previous constraints.
   * <p/>
   * <li> The corner components, if provided, are aligned with the
   * ends of the scrollbars and headers. If there is a vertical
   * scrollbar, the right corners appear; if there is a horizontal
   * scrollbar, the lower corners appear; a row header gets left
   * corners, and a column header gets upper corners.
   * </ul>
   * 
   * @param parent the <code>Container</code> to lay out
   */
  @Override
  public void layoutContainer(Container parent) {
    /* Sync the (now obsolete) policy fields with the
     * JScrollPane.
     */
    JScrollPane scrollPane = (JScrollPane)parent;
    vsbPolicy = scrollPane.getVerticalScrollBarPolicy();
    hsbPolicy = scrollPane.getHorizontalScrollBarPolicy();

    Rectangle availR = scrollPane.getBounds();
    availR.x = availR.y = 0;

    Insets insets = parent.getInsets();
    availR.x = insets.left;
    availR.y = insets.top;
    availR.width -= insets.left + insets.right;
    availR.height -= insets.top + insets.bottom;

    /* Get the scrollPane's orientation.
     */
    boolean leftToRight = false;

    /* If there's a visible column header remove the space it
     * needs from the top of availR.  The column header is treated
     * as if it were fixed height, arbitrary width.
     */

    Rectangle colHeadR = new Rectangle(0, availR.y, 0, 0);

    if ((colHead != null) && (colHead.isVisible())) {
      int colHeadHeight = Math.min(availR.height,
                                   colHead.getPreferredSize().height);
      colHeadR.height = colHeadHeight;
      availR.y += colHeadHeight;
      availR.height -= colHeadHeight;
    }

    /* If there's a visible row header remove the space it needs
     * from the left or right of availR.  The row header is treated
     * as if it were fixed width, arbitrary height.
     */

    Rectangle rowHeadR = new Rectangle(0, 0, 0, 0);

    if ((rowHead != null) && (rowHead.isVisible())) {
      int rowHeadWidth = Math.min(availR.width,
                                  rowHead.getPreferredSize().width);
      rowHeadR.width = rowHeadWidth;
      availR.width -= rowHeadWidth;
      if (leftToRight) {
        rowHeadR.x = availR.x;
        availR.x += rowHeadWidth;
      }
      else {
        rowHeadR.x = availR.x + availR.width;
      }
    }

    /* If there's a JScrollPane.viewportBorder, remove the
     * space it occupies for availR.
     */

    Border viewportBorder = scrollPane.getViewportBorder();
    Insets vpbInsets;
    if (viewportBorder != null) {
      vpbInsets = viewportBorder.getBorderInsets(parent);
      availR.x += vpbInsets.left;
      availR.y += vpbInsets.top;
      availR.width -= vpbInsets.left + vpbInsets.right;
      availR.height -= vpbInsets.top + vpbInsets.bottom;
    }
    else {
      vpbInsets = new Insets(0, 0, 0, 0);
    }


    /* At this point availR is the space available for the viewport
     * and scrollbars. rowHeadR is correct except for its height and y
     * and colHeadR is correct except for its width and x.  Once we're
     * through computing the dimensions  of these three parts we can
     * go back and set the dimensions of rowHeadR.height, rowHeadR.y,
     * colHeadR.width, colHeadR.x and the bounds for the corners.
     *
     * We'll decide about putting up scrollbars by comparing the
     * viewport views preferred size with the viewports extent
     * size (generally just its size).  Using the preferredSize is
     * reasonable because layout proceeds top down - so we expect
     * the viewport to be laid out next.  And we assume that the
     * viewports layout manager will give the view it's preferred
     * size.  One exception to this is when the view implements
     * Scrollable and Scrollable.getViewTracksViewport{Width,Height}
     * methods return true.  If the view is tracking the viewports
     * width we don't bother with a horizontal scrollbar, similarly
     * if view.getViewTracksViewport(Height) is true we don't bother
     * with a vertical scrollbar.
     */

    Component view = (viewport != null) ? viewport.getView() : null;
    Dimension viewPrefSize =
      (view != null) ? view.getPreferredSize()
      : new Dimension(0, 0);

    Dimension extentSize =
      (viewport != null) ? viewport.toViewCoordinates(availR.getSize())
      : new Dimension(0, 0);

    boolean viewTracksViewportWidth = false;
    boolean viewTracksViewportHeight = false;
    boolean isEmpty = (availR.width < 0 || availR.height < 0);
    Scrollable sv;
    // Don't bother checking the Scrollable methods if there is no room
    // for the viewport, we aren't going to show any scrollbars in this
    // case anyway.
    if (!isEmpty && view instanceof Scrollable) {
      sv = (Scrollable)view;
      viewTracksViewportWidth = sv.getScrollableTracksViewportWidth();
      viewTracksViewportHeight = sv.getScrollableTracksViewportHeight();
    }
    else {
      sv = null;
    }

    /* If there's a vertical scrollbar and we need one, allocate
     * space for it (we'll make it visible later). A vertical
     * scrollbar is considered to be fixed width, arbitrary height.
     */

    Rectangle vsbR = new Rectangle(0, availR.y - vpbInsets.top, 0, 0);

    boolean vsbNeeded;
    if (isEmpty) {
      vsbNeeded = false;
    }
    else if (vsbPolicy == VERTICAL_SCROLLBAR_ALWAYS) {
      vsbNeeded = true;
    }
    else if (vsbPolicy == VERTICAL_SCROLLBAR_NEVER) {
      vsbNeeded = false;
    }
    else {  // vsbPolicy == VERTICAL_SCROLLBAR_AS_NEEDED
      vsbNeeded = !viewTracksViewportHeight && (viewPrefSize.height > extentSize.height);
    }


    if ((vsb != null) && vsbNeeded) {
      adjustForVSB(true, availR, vsbR, vpbInsets, leftToRight);
      extentSize = viewport.toViewCoordinates(availR.getSize());
    }

    /* If there's a horizontal scrollbar and we need one, allocate
     * space for it (we'll make it visible later). A horizontal
     * scrollbar is considered to be fixed height, arbitrary width.
     */

    Rectangle hsbR = new Rectangle(availR.x - vpbInsets.left, 0, 0, 0);
    boolean hsbNeeded;
    if (isEmpty) {
      hsbNeeded = false;
    }
    else if (hsbPolicy == HORIZONTAL_SCROLLBAR_ALWAYS) {
      hsbNeeded = true;
    }
    else if (hsbPolicy == HORIZONTAL_SCROLLBAR_NEVER) {
      hsbNeeded = false;
    }
    else {  // hsbPolicy == HORIZONTAL_SCROLLBAR_AS_NEEDED
      hsbNeeded = !viewTracksViewportWidth && (viewPrefSize.width > extentSize.width);
    }

    if ((hsb != null) && hsbNeeded) {
      adjustForHSB(true, availR, hsbR, vpbInsets);

      /* If we added the horizontal scrollbar then we've implicitly
       * reduced  the vertical space available to the viewport.
       * As a consequence we may have to add the vertical scrollbar,
       * if that hasn't been done so already.  Of course we
       * don't bother with any of this if the vsbPolicy is NEVER.
       */
      if ((vsb != null) && !vsbNeeded &&
          (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {

        extentSize = viewport.toViewCoordinates(availR.getSize());
        vsbNeeded = viewPrefSize.height > extentSize.height;

        if (vsbNeeded) {
          adjustForVSB(true, availR, vsbR, vpbInsets, leftToRight);
        }
      }
    }

    /* Set the size of the viewport first, and then recheck the Scrollable
     * methods. Some components base their return values for the Scrollable
     * methods on the size of the Viewport, so that if we don't
     * ask after resetting the bounds we may have gotten the wrong
     * answer.
     */

    if (viewport != null) {
      viewport.setBounds(availR);

      if (sv != null) {
        extentSize = viewport.toViewCoordinates(availR.getSize());

        boolean oldHSBNeeded = hsbNeeded;
        boolean oldVSBNeeded = vsbNeeded;
        viewTracksViewportWidth = sv.
          getScrollableTracksViewportWidth();
        viewTracksViewportHeight = sv.
          getScrollableTracksViewportHeight();
        if (vsb != null && vsbPolicy == VERTICAL_SCROLLBAR_AS_NEEDED) {
          boolean newVSBNeeded = !viewTracksViewportHeight &&
                                 (viewPrefSize.height > extentSize.height);
          if (newVSBNeeded != vsbNeeded) {
            vsbNeeded = newVSBNeeded;
            adjustForVSB(vsbNeeded, availR, vsbR, vpbInsets,
                         leftToRight);
            extentSize = viewport.toViewCoordinates
              (availR.getSize());
          }
        }
        if (hsb != null && hsbPolicy == HORIZONTAL_SCROLLBAR_AS_NEEDED) {
          boolean newHSBbNeeded = !viewTracksViewportWidth &&
                                  (viewPrefSize.width > extentSize.width);
          if (newHSBbNeeded != hsbNeeded) {
            hsbNeeded = newHSBbNeeded;
            adjustForHSB(hsbNeeded, availR, hsbR, vpbInsets);
            if ((vsb != null) && !vsbNeeded &&
                (vsbPolicy != VERTICAL_SCROLLBAR_NEVER)) {

              extentSize = viewport.toViewCoordinates
                (availR.getSize());
              vsbNeeded = viewPrefSize.height >
                          extentSize.height;

              if (vsbNeeded) {
                adjustForVSB(true, availR, vsbR, vpbInsets,
                             leftToRight);
              }
            }
          }
        }
        if (oldHSBNeeded != hsbNeeded ||
            oldVSBNeeded != vsbNeeded) {
          viewport.setBounds(availR);
          // You could argue that we should recheck the
          // Scrollable methods again until they stop changing,
          // but they might never stop changing, so we stop here
          // and don't do any additional checks.
        }
      }
    }

    /* We now have the final size of the viewport: availR.
     * Now fixup the header and scrollbar widths/heights.
     */
    vsbR.height = availR.height + vpbInsets.top + vpbInsets.bottom;
    hsbR.width = availR.width + vpbInsets.left + vpbInsets.right;
    rowHeadR.height = availR.height + vpbInsets.top + vpbInsets.bottom;
    rowHeadR.y = availR.y - vpbInsets.top;
    colHeadR.width = availR.width + vpbInsets.left + vpbInsets.right;
    colHeadR.x = availR.x - vpbInsets.left;

    /* Set the bounds of the remaining components.  The scrollbars
     * are made invisible if they're not needed.
     */

    if (rowHead != null) {
      rowHead.setBounds(rowHeadR);
    }

    if (colHead != null) {
      colHead.setBounds(colHeadR);
    }

    if (vsb != null) {
      if (vsbNeeded) {
        vsb.setVisible(true);
        vsb.setBounds(vsbR);
      }
      else {
        vsb.setVisible(false);
      }
    }

    if (hsb != null) {
      if (hsbNeeded) {
        hsb.setVisible(true);
        hsb.setBounds(hsbR);
      }
      else {
        hsb.setVisible(false);
      }
    }

    if (lowerLeft != null) {
      lowerLeft.setBounds(leftToRight ? rowHeadR.x : vsbR.x,
                          hsbR.y,
                          leftToRight ? rowHeadR.width : vsbR.width,
                          hsbR.height);
    }

    if (lowerRight != null) {
      lowerRight.setBounds(leftToRight ? vsbR.x : rowHeadR.x,
                           hsbR.y,
                           leftToRight ? vsbR.width : rowHeadR.width,
                           hsbR.height);
    }

    if (upperLeft != null) {
      upperLeft.setBounds(leftToRight ? rowHeadR.x : vsbR.x,
                          colHeadR.y,
                          leftToRight ? rowHeadR.width : vsbR.width,
                          colHeadR.height);
    }

    if (upperRight != null) {
      upperRight.setBounds(leftToRight ? vsbR.x : rowHeadR.x,
                           colHeadR.y,
                           leftToRight ? vsbR.width : rowHeadR.width,
                           colHeadR.height);
    }
  }

  /**
   * Adjusts the <code>Rectangle</code> <code>available</code> based on if
   * the vertical scrollbar is needed (<code>wantsVSB</code>).
   * The location of the vsb is updated in <code>vsbR</code>, and
   * the viewport border insets (<code>vpbInsets</code>) are used to offset
   * the vsb. This is only called when <code>wantsVSB</code> has
   * changed, eg you shouldn't invoke adjustForVSB(true) twice.
   */
  private void adjustForVSB(boolean wantsVSB, Rectangle available,
                            Rectangle vsbR, Insets vpbInsets,
                            boolean leftToRight) {
    int oldWidth = vsbR.width;
    if (wantsVSB) {
      int vsbWidth = Math.max(0, Math.min(vsb.getPreferredSize().width,
                                          available.width));

      available.width -= vsbWidth;
      vsbR.width = vsbWidth;

      if (leftToRight) {
        vsbR.x = available.x + available.width + vpbInsets.right;
      }
      else {
        vsbR.x = available.x - vpbInsets.left;
        available.x += vsbWidth;
      }
    }
    else {
      available.width += oldWidth;
    }
  }

  /**
   * Adjusts the <code>Rectangle</code> <code>available</code> based on if
   * the horizontal scrollbar is needed (<code>wantsHSB</code>).
   * The location of the hsb is updated in <code>hsbR</code>, and
   * the viewport border insets (<code>vpbInsets</code>) are used to offset
   * the hsb.  This is only called when <code>wantsHSB</code> has
   * changed, eg you shouldn't invoked adjustForHSB(true) twice.
   */
  private void adjustForHSB(boolean wantsHSB, Rectangle available,
                            Rectangle hsbR, Insets vpbInsets) {
    int oldHeight = hsbR.height;
    if (wantsHSB) {
      int hsbHeight = Math.max(0, Math.min(available.height,
                                           hsb.getPreferredSize().height));

      available.height -= hsbHeight;
      hsbR.y = available.y + available.height + vpbInsets.bottom;
      hsbR.height = hsbHeight;
    }
    else {
      available.height += oldHeight;
    }
  }


  /**
   * Returns the bounds of the border around the specified scroll pane's
   * viewport.
   * 
   * @return the size and position of the viewport border
   * @deprecated As of JDK version Swing1.1
   *             replaced by <code>JScrollPane.getViewportBorderBounds()</code>.
   */
  @Override
  public Rectangle getViewportBorderBounds(JScrollPane scrollpane) {
    return scrollpane.getViewportBorderBounds();
  }

}