/**
 * A class that provides scrolling capabilities to a long menu dropdown or
 * popup menu.  A number of items can optionally be frozen at the top and/or
 * bottom of the menu.
 * <P>
 * <B>Implementation note:</B>  The default number of items to display
 * at a time is 15, and the default scrolling interval is 125 milliseconds.
 * <P>
 *
 * @version 1.5.0 04/05/12
 * @author Darryl
 * https://tips4java.wordpress.com/2009/02/01/menu-scroller/
 */
 
import javax.swing.Icon;

sclass JMenuScroller {

  VF1<JPopupMenu> fillMenu;
  private JPopupMenu menu;
  private Component[] menuItems;
  private MenuScrollItem upItem;
  private MenuScrollItem downItem;
  private final MenuScrollListener menuListener = new MenuScrollListener();
  private int scrollCount;
  private int interval;
  private int topFixedCount;
  private int bottomFixedCount;
  private int firstIndex = 0;
  private int keepVisibleIndex = -1;

  /**
   * Registers a menu to be scrolled with the default number of items to
   * display at a time and the default scrolling interval.
   * 
   * @param menu the menu
   * @return the JMenuScroller
   */
  public static JMenuScroller setScrollerFor(JMenu menu) {
    return new JMenuScroller(menu);
  }

  /**
   * Registers a popup menu to be scrolled with the default number of items to
   * display at a time and the default scrolling interval.
   * 
   * @param menu the popup menu
   * @return the JMenuScroller
   */
  public static JMenuScroller setScrollerFor(JPopupMenu menu) {
    return new JMenuScroller(menu);
  }

  /**
   * Registers a menu to be scrolled with the default number of items to
   * display at a time and the specified scrolling interval.
   * 
   * @param menu the menu
   * @param scrollCount the number of items to display at a time
   * @return the JMenuScroller
   * @throws IllegalArgumentException if scrollCount is 0 or negative
   */
  public static JMenuScroller setScrollerFor(JMenu menu, int scrollCount) {
    return new JMenuScroller(menu, scrollCount);
  }

  /**
   * Registers a popup menu to be scrolled with the default number of items to
   * display at a time and the specified scrolling interval.
   * 
   * @param menu the popup menu
   * @param scrollCount the number of items to display at a time
   * @return the JMenuScroller
   * @throws IllegalArgumentException if scrollCount is 0 or negative
   */
  public static JMenuScroller setScrollerFor(JPopupMenu menu, int scrollCount) {
    return new JMenuScroller(menu, scrollCount);
  }

  /**
   * Registers a menu to be scrolled, with the specified number of items to
   * display at a time and the specified scrolling interval.
   * 
   * @param menu the menu
   * @param scrollCount the number of items to be displayed at a time
   * @param interval the scroll interval, in milliseconds
   * @return the JMenuScroller
   * @throws IllegalArgumentException if scrollCount or interval is 0 or negative
   */
  public static JMenuScroller setScrollerFor(JMenu menu, int scrollCount, int interval) {
    return new JMenuScroller(menu, scrollCount, interval);
  }

  /**
   * Registers a popup menu to be scrolled, with the specified number of items to
   * display at a time and the specified scrolling interval.
   * 
   * @param menu the popup menu
   * @param scrollCount the number of items to be displayed at a time
   * @param interval the scroll interval, in milliseconds
   * @return the JMenuScroller
   * @throws IllegalArgumentException if scrollCount or interval is 0 or negative
   */
  public static JMenuScroller setScrollerFor(JPopupMenu menu, int scrollCount, int interval) {
    return new JMenuScroller(menu, scrollCount, interval);
  }

  /**
   * Registers a menu to be scrolled, with the specified number of items
   * to display in the scrolling region, the specified scrolling interval,
   * and the specified numbers of items fixed at the top and bottom of the
   * menu.
   * 
   * @param menu the menu
   * @param scrollCount the number of items to display in the scrolling portion
   * @param interval the scroll interval, in milliseconds
   * @param topFixedCount the number of items to fix at the top.  May be 0.
   * @param bottomFixedCount the number of items to fix at the bottom. May be 0
   * @throws IllegalArgumentException if scrollCount or interval is 0 or
   * negative or if topFixedCount or bottomFixedCount is negative
   * @return the JMenuScroller
   */
  public static JMenuScroller setScrollerFor(JMenu menu, int scrollCount, int interval,
          int topFixedCount, int bottomFixedCount) {
    return new JMenuScroller(menu, scrollCount, interval,
            topFixedCount, bottomFixedCount);
  }

  /**
   * Registers a popup menu to be scrolled, with the specified number of items
   * to display in the scrolling region, the specified scrolling interval,
   * and the specified numbers of items fixed at the top and bottom of the
   * popup menu.
   * 
   * @param menu the popup menu
   * @param scrollCount the number of items to display in the scrolling portion
   * @param interval the scroll interval, in milliseconds
   * @param topFixedCount the number of items to fix at the top.  May be 0
   * @param bottomFixedCount the number of items to fix at the bottom.  May be 0
   * @throws IllegalArgumentException if scrollCount or interval is 0 or
   * negative or if topFixedCount or bottomFixedCount is negative
   * @return the JMenuScroller
   */
  public static JMenuScroller setScrollerFor(JPopupMenu menu, int scrollCount, int interval,
          int topFixedCount, int bottomFixedCount) {
    return new JMenuScroller(menu, scrollCount, interval,
            topFixedCount, bottomFixedCount);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a menu with the
   * default number of items to display at a time, and default scrolling
   * interval.
   * 
   * @param menu the menu
   */
  public JMenuScroller(JMenu menu) {
    this(menu, 15);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a popup menu with the
   * default number of items to display at a time, and default scrolling
   * interval.
   * 
   * @param menu the popup menu
   */
  public JMenuScroller(JPopupMenu menu) {
    this(menu, 15);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a menu with the
   * specified number of items to display at a time, and default scrolling
   * interval.
   * 
   * @param menu the menu
   * @param scrollCount the number of items to display at a time
   * @throws IllegalArgumentException if scrollCount is 0 or negative
   */
  public JMenuScroller(JMenu menu, int scrollCount) {
    this(menu, scrollCount, 150);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a popup menu with the
   * specified number of items to display at a time, and default scrolling
   * interval.
   * 
   * @param menu the popup menu
   * @param scrollCount the number of items to display at a time
   * @throws IllegalArgumentException if scrollCount is 0 or negative
   */
  public JMenuScroller(JPopupMenu menu, int scrollCount) {
    this(menu, scrollCount, 150);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a menu with the
   * specified number of items to display at a time, and specified scrolling
   * interval.
   * 
   * @param menu the menu
   * @param scrollCount the number of items to display at a time
   * @param interval the scroll interval, in milliseconds
   * @throws IllegalArgumentException if scrollCount or interval is 0 or negative
   */
  public JMenuScroller(JMenu menu, int scrollCount, int interval) {
    this(menu, scrollCount, interval, 0, 0);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a popup menu with the
   * specified number of items to display at a time, and specified scrolling
   * interval.
   * 
   * @param menu the popup menu
   * @param scrollCount the number of items to display at a time
   * @param interval the scroll interval, in milliseconds
   * @throws IllegalArgumentException if scrollCount or interval is 0 or negative
   */
  public JMenuScroller(JPopupMenu menu, int scrollCount, int interval) {
    this(menu, scrollCount, interval, 0, 0);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a menu with the
   * specified number of items to display in the scrolling region, the
   * specified scrolling interval, and the specified numbers of items fixed at
   * the top and bottom of the menu.
   * 
   * @param menu the menu
   * @param scrollCount the number of items to display in the scrolling portion
   * @param interval the scroll interval, in milliseconds
   * @param topFixedCount the number of items to fix at the top.  May be 0
   * @param bottomFixedCount the number of items to fix at the bottom.  May be 0
   * @throws IllegalArgumentException if scrollCount or interval is 0 or
   * negative or if topFixedCount or bottomFixedCount is negative
   */
  public JMenuScroller(JMenu menu, int scrollCount, int interval,
          int topFixedCount, int bottomFixedCount) {
    this(menu.getPopupMenu(), scrollCount, interval, topFixedCount, bottomFixedCount);
  }

  /**
   * Constructs a <code>JMenuScroller</code> that scrolls a popup menu with the
   * specified number of items to display in the scrolling region, the
   * specified scrolling interval, and the specified numbers of items fixed at
   * the top and bottom of the popup menu.
   * 
   * @param menu the popup menu
   * @param scrollCount the number of items to display in the scrolling portion
   * @param interval the scroll interval, in milliseconds
   * @param topFixedCount the number of items to fix at the top.  May be 0
   * @param bottomFixedCount the number of items to fix at the bottom.  May be 0
   * @throws IllegalArgumentException if scrollCount or interval is 0 or
   * negative or if topFixedCount or bottomFixedCount is negative
   */
  public JMenuScroller(JPopupMenu menu, int scrollCount, int interval,
          int topFixedCount, int bottomFixedCount) {
    if (scrollCount <= 0 || interval <= 0) {
      throw new IllegalArgumentException("scrollCount and interval must be greater than 0");
    }
    if (topFixedCount < 0 || bottomFixedCount < 0) {
      throw new IllegalArgumentException("topFixedCount and bottomFixedCount cannot be negative");
    }

    upItem = new MenuScrollItem(UP, -1);
    downItem = new MenuScrollItem(DOWN, +1);
    setScrollCount(scrollCount);
    setInterval(interval);
    setTopFixedCount(topFixedCount);
    setBottomFixedCount(bottomFixedCount);

    this.menu = menu;
    menu.addPopupMenuListener(menuListener);
  }

  /**
   * Returns the scroll interval in milliseconds
   * 
   * @return the scroll interval in milliseconds
   */
  public int getInterval() {
    return interval;
  }

  /**
   * Sets the scroll interval in milliseconds
   * 
   * @param interval the scroll interval in milliseconds
   * @throws IllegalArgumentException if interval is 0 or negative
   */
  public void setInterval(int interval) {
    if (interval <= 0) {
      throw new IllegalArgumentException("interval must be greater than 0");
    }
    upItem.setInterval(interval);
    downItem.setInterval(interval);
    this.interval = interval;
  }

  /**
   * Returns the number of items in the scrolling portion of the menu.
   *
   * @return the number of items to display at a time
   */
  public int getscrollCount() {
    return scrollCount;
  }

  /**
   * Sets the number of items in the scrolling portion of the menu.
   * 
   * @param scrollCount the number of items to display at a time
   * @throws IllegalArgumentException if scrollCount is 0 or negative
   */
  public void setScrollCount(int scrollCount) {
    if (scrollCount <= 0) {
      throw new IllegalArgumentException("scrollCount must be greater than 0");
    }
    this.scrollCount = scrollCount;
    // XXX the following line closes all menus then this menu is made.
    // That doesn't seem right.
    // MenuSelectionManager.defaultManager().clearSelectedPath();
  }

  /**
   * Returns the number of items fixed at the top of the menu or popup menu.
   * 
   * @return the number of items
   */
  public int getTopFixedCount() {
    return topFixedCount;
  }

  /**
   * Sets the number of items to fix at the top of the menu or popup menu.
   * 
   * @param topFixedCount the number of items
   */
  public void setTopFixedCount(int topFixedCount) {
    if (firstIndex <= topFixedCount) {
      firstIndex = topFixedCount;
    } else {
      firstIndex += (topFixedCount - this.topFixedCount);
    }
    this.topFixedCount = topFixedCount;
  }

  /**
   * Returns the number of items fixed at the bottom of the menu or popup menu.
   * 
   * @return the number of items
   */
  public int getBottomFixedCount() {
    return bottomFixedCount;
  }

  /**
   * Sets the number of items to fix at the bottom of the menu or popup menu.
   * 
   * @param bottomFixedCount the number of items
   */
  public void setBottomFixedCount(int bottomFixedCount) {
    this.bottomFixedCount = bottomFixedCount;
  }

  /**
   * Scrolls the specified item into view each time the menu is opened.  Call this method with
   * <code>null</code> to restore the default behavior, which is to show the menu as it last
   * appeared.
   *
   * @param item the item to keep visible
   * @see #keepVisible(int)
   */
  public void keepVisible(JMenuItem item) {
    if (item == null) {
      keepVisibleIndex = -1;
    } else {
      int index = menu.getComponentIndex(item);
      keepVisibleIndex = index;
    }
  }

  /**
   * Scrolls the item at the specified index into view each time the menu is opened.  Call this
   * method with <code>-1</code> to restore the default behavior, which is to show the menu as
   * it last appeared.
   *
   * @param index the index of the item to keep visible
   * @see #keepVisible(javax.swing.JMenuItem)
   */
  public void keepVisible(int index) {
    keepVisibleIndex = index;
  }

  /**
   * Removes this JMenuScroller from the associated menu and restores the
   * default behavior of the menu.
   */
  public void dispose() {
    if (menu != null) {
      menu.removePopupMenuListener(menuListener);
      menu = null;
    }
  }

  /**
   * Ensures that the <code>dispose</code> method of this JMenuScroller is
   * called when there are no more refrences to it.
   * 
   * @exception  Throwable if an error occurs.
   * @see JMenuScroller#dispose()
   */
  @Override
  public void finalize() throws Throwable {
    dispose();
  }

  private void refreshMenu() {
    if (menuItems != null && menuItems.length > 0) {
      firstIndex = Math.max(topFixedCount, firstIndex);
      firstIndex = Math.min(menuItems.length - bottomFixedCount - scrollCount, firstIndex);

      upItem.setEnabled(firstIndex > topFixedCount);
      downItem.setEnabled(firstIndex + scrollCount < menuItems.length - bottomFixedCount);

      menu.removeAll();
      for (int i = 0; i < topFixedCount; i++) {
        menu.add(menuItems[i]);
      }
      if (topFixedCount > 0) {
        menu.addSeparator();
      }

      menu.add(upItem);
      for (int i = firstIndex; i < scrollCount + firstIndex; i++) {
        menu.add(menuItems[i]);
      }
      menu.add(downItem);

      if (bottomFixedCount > 0) {
        menu.addSeparator();
      }
      for (int i = menuItems.length - bottomFixedCount; i < menuItems.length; i++) {
        menu.add(menuItems[i]);
      }

      JComponent parent = (JComponent) upItem.getParent();
      parent.revalidate();
      parent.repaint();
    }
  }

  private class MenuScrollListener implements PopupMenuListener {

    @Override
    public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
      if (fillMenu != null) {
        clearPopupMenu(menu);
        callF(fillMenu, menu);
      }
      setMenuItems();
    }

    @Override
    public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
      if (fillMenu != null) clearPopupMenu(menu);
      else restoreMenuItems();
    }

    @Override
    public void popupMenuCanceled(PopupMenuEvent e) {
      if (fillMenu != null) clearPopupMenu(menu);
      else restoreMenuItems();
    }

    private void setMenuItems() {
      menuItems = menu.getComponents();
      if (keepVisibleIndex >= topFixedCount
              && keepVisibleIndex <= menuItems.length - bottomFixedCount
              && (keepVisibleIndex > firstIndex + scrollCount
              || keepVisibleIndex < firstIndex)) {
        firstIndex = Math.min(firstIndex, keepVisibleIndex);
        firstIndex = Math.max(firstIndex, keepVisibleIndex - scrollCount + 1);
      }
      if (menuItems.length > topFixedCount + scrollCount + bottomFixedCount) {
        refreshMenu();
      }
    }

    private void restoreMenuItems() {
      menu.removeAll();
      for (Component component : menuItems) {
        menu.add(component);
      }
    }
  }

  private class MenuScrollTimer extends javax.swing.Timer {

    public MenuScrollTimer(final int increment, int interval) {
      super(interval, new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
          firstIndex += increment;
          refreshMenu();
        }
      });
    }
  }

  private class MenuScrollItem extends JMenuItem
          implements ChangeListener {

    private MenuScrollTimer timer;

    public MenuScrollItem(MenuIcon icon, int increment) {
      setIcon(icon);
      setDisabledIcon(icon);
      timer = new MenuScrollTimer(increment, interval);
      addChangeListener(this);
    }

    public void setInterval(int interval) {
      timer.setDelay(interval);
    }

    @Override
    public void stateChanged(ChangeEvent e) {
      if (isArmed() && !timer.isRunning()) {
        timer.start();
      }
      if (!isArmed() && timer.isRunning()) {
        timer.stop();
      }
    }
  }

  static MenuIcon UP = new MenuIcon(9, 1, 9);
  static MenuIcon DOWN = new MenuIcon(1, 9, 1);
    
  private sclass MenuIcon implements Icon {

    final int[] xPoints = {1, 5, 9};
    final int[] yPoints;

    MenuIcon(int... yPoints) {
      this.yPoints = yPoints;
    }

    @Override
    public void paintIcon(Component c, Graphics g, int x, int y) {
      Dimension size = c.getSize();
      Graphics g2 = g.create(size.width / 2 - 5, size.height / 2 - 5, 10, 10);
      g2.setColor(Color.GRAY);
      g2.drawPolygon(xPoints, yPoints, 3);
      if (c.isEnabled()) {
        g2.setColor(Color.BLACK);
        g2.fillPolygon(xPoints, yPoints, 3);
      }
      g2.dispose();
    }

    @Override
    public int getIconWidth() {
      return 0;
    }

    @Override
    public int getIconHeight() {
      return 10;
    }
  }
}