/*******************************************************************************
 * Copyright (c) 2006, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
module org.eclipse.jface.internal.databinding.provisional.swt.MenuUpdater;

import java.lang.all;

import org.eclipse.core.databinding.observable.ChangeEvent;
import org.eclipse.core.databinding.observable.IChangeListener;
import org.eclipse.core.databinding.observable.IObservable;
import org.eclipse.core.databinding.observable.ObservableTracker;
import org.eclipse.swt.events.DisposeEvent;
import org.eclipse.swt.events.DisposeListener;
import org.eclipse.swt.events.MenuEvent;
import org.eclipse.swt.events.MenuListener;
import org.eclipse.swt.widgets.Menu;

/**
 * NON-API - A MenuUpdater updates an SWT menu in response to changes in the model. By
 * wrapping a block of code in a MenuUpdater, clients can rely on the fact that
 * the block of code will be re-executed whenever anything changes in the model
 * that might affect its behavior.
 * 
 * <p>
 * MenuUpdaters only execute once their menus are shown. If something changes in
 * the model, the updater is flagged as dirty and it stops listening to the
 * model until the next time the menu is shown. If the menu is visible while the
 * model changes, it will be updated right away.
 * </p>
 * 
 * <p>
 * Clients should subclass this when copying information from the model to a
 * menu. Typical usage:
 * </p>
 * 
 * <ul>
 * <li>Override updateMenu. It should do whatever is necessary to display the
 * contents of the model in the menu.</li>
 * <li>In the constructor, attach listeners to the model. The listeners should
 * call markDirty whenever anything changes in the model that affects
 * updateMenu. Note: this step can be omitted when calling any method tagged
 * with "@TrackedGetter" since MenuUpdater will automatically attach a listener
 * to any object if a "@TrackedGetter" method is called in updateMenu.</li>
 * <li>(optional)Extend dispose() to remove any listeners attached in the
 * constructor</li>
 * </ul>
 * 
 * @since 1.1
 */
public abstract class MenuUpdater {
    
    private class PrivateInterface : MenuListener, 
        DisposeListener, Runnable, IChangeListener {

        // DisposeListener implementation
        public void widgetDisposed(DisposeEvent e) {
            this.outer.dispose();
        }
        
        // Runnable implementation. This method runs at most once per repaint whenever the
        // value gets marked as dirty.
        public void run() {
            if (theMenu !is null && !theMenu.isDisposed() && theMenu.isVisible()) {
                updateIfNecessary();
            }
        }
        
        // IChangeListener implementation (listening to the ComputedValue)
        public void handleChange(ChangeEvent event) {
            // Whenever this updator becomes dirty, schedule the run() method 
            makeDirty();
        }

        public void menuHidden(MenuEvent e) {
            // do nothing
        }

        public void menuShown(MenuEvent e) {
            updateIfNecessary();
        }
        
    }
    
    private Runnable updateRunnable = new class() Runnable {
        public void run() {
            updateMenu();
        }
    };
    
    private PrivateInterface privateInterface = new PrivateInterface();
    private Menu theMenu;
    private IObservable[] dependencies = new IObservable[0];
    private bool dirty = false;
    
    /**
     * Creates an updator for the given menu.  
     * 
     * @param toUpdate menu to update
     */
    public this(Menu toUpdate) {
        theMenu = toUpdate;
        
        theMenu.addDisposeListener(privateInterface);
        theMenu.addMenuListener(privateInterface);
        makeDirty();
    }
    
    private void updateIfNecessary() {
        if (dirty) {
            dependencies = ObservableTracker.runAndMonitor(updateRunnable, privateInterface, null);
            dirty = false;
        }
    }

    /**
     * This is called automatically when the menu is disposed. It may also
     * be called explicitly to remove this updator from the menu. Subclasses
     * will normally extend this method to detach any listeners they attached
     * in their constructor.
     */
    public void dispose() {
        theMenu.removeDisposeListener(privateInterface);
        theMenu.removeMenuListener(privateInterface);

        stopListening();
    }

    private void stopListening() {
        // Stop listening for dependency changes
        for (int i = 0; i < dependencies.length; i++) {
            IObservable observable = dependencies[i];
                
            observable.removeChangeListener(privateInterface);
        }
    }

    /**
     * Updates the menu. This method will be invoked once after the
     * updater is created, and once for any SWT.Show event if this 
     * updater is marked as dirty at that time.
     *  
     * <p>
     * Subclasses should overload this method to provide any code that 
     * udates the menu.
     * </p>
     */
    protected abstract void updateMenu();
    
    /**
     * Marks this updator as dirty. Causes the updateControl method to
     * be invoked before the next time the control is repainted.
     */
    protected final void makeDirty() {
        if (!dirty) {
            dirty = true;
            stopListening();
            SWTUtil.runOnce(theMenu.getDisplay(), privateInterface);
        }
    }
    
}