/*******************************************************************************
 * Copyright (c) 2005, 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.ControlUpdater;

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.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.widgets.Control;

/**
 * NON-API - A ControlUpdater updates an SWT control in response to changes in the model.
 * By wrapping a block of code in a ControlUpdater, 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>
 * ControlUpdaters only execute when their controls are visible. If something changes
 * in the model while the control is invisible, the updator is flagged as dirty and
 * the updator stops listening to the model until the next time the control repaints.
 * This saves CPU cycles by deferring UI updates to widgets that are currently invisible.
 * </p>
 * 
 * <p>
 * Clients should subclass this when copying information from the model to
 * a control. Typical usage:
 * </p>
 * 
 * <ul>
 * <li>Override updateControl. It should do whatever is necessary to display
 *     the contents of the model in the control.</li>
 * <li>In the constructor, attach listeners to the model. The listeners should 
 *     call markDirty whenever anything changes in the model that affects 
 *     updateControl. Note: this step can be omitted when calling any method
 *     tagged with "@TrackedGetter" since ControlUpdater will automatically attach
 *     a listener to any object if a "@TrackedGetter" method is called in
 *     updateControl.</li>
 * <li>(optional)Extend dispose() to remove any listeners attached in the constructor</li>
 * </ul>
 * 
 * <p>
 * Example:
 * </p>
 * 
 * <code>
 * // Displays an observable value in a label and keeps the label in synch with changes
 * // in the value.
 * IReadableValue someValue = ...
 * final Label myLabel = new Label(parent, SWT.NONE);
 * new ControlUpdater(myLabel) {
 *      protected void updateControl() {
 *         myLabel.setText(someValue.getValue().toString);
 *      }
 * }
 * // myLabel will display the value of someValue the next time it repaints, and will automatically
 * // be updated whenever someValue changes and the label is visible
 * </code>
 * 
 * @since 1.1
 */
public abstract class ControlUpdater {
    
    private class PrivateInterface : PaintListener, 
        DisposeListener, Runnable, IChangeListener {
        
        // PaintListener implementation
        public void paintControl(PaintEvent e) {
            updateIfNecessary();
        }

        // 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 (theControl !is null && !theControl.isDisposed() && theControl.isVisible()) {
                updateIfNecessary();
            }
        }
        
        // IChangeListener implementation (listening to the ComputedValue)
        public void handleChange(ChangeEvent event) {
            // Whenever this updator becomes dirty, schedule the run() method 
            makeDirty();
        }
        
    }
    
    private Runnable updateRunnable = new class() Runnable {
        public void run() {
            updateControl();
        }
    };
    
    private PrivateInterface privateInterface = new PrivateInterface();
    private Control theControl;
    private IObservable[] dependencies = new IObservable[0];
    private bool dirty = false;
    
    /**
     * Creates an updater for the given control.  
     * 
     * @param toUpdate control to update
     */
    public this(Control toUpdate) {
        theControl = toUpdate;
        
        theControl.addDisposeListener(privateInterface);
        theControl.addPaintListener(privateInterface);
        makeDirty();
    }
    
    private void updateIfNecessary() {
        if (dirty) {
            dependencies = ObservableTracker.runAndMonitor(updateRunnable, privateInterface, null);
            dirty = false;
        }
    }

    /**
     * This is called automatically when the control is disposed. It may also
     * be called explicitly to remove this updator from the control. Subclasses
     * will normally extend this method to detach any listeners they attached
     * in their constructor.
     */
    public void dispose() {
        theControl.removeDisposeListener(privateInterface);
        theControl.removePaintListener(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 control. This method will be invoked once after the
     * updator is created, and once before any repaint during which the 
     * control is visible and dirty.
     *  
     * <p>
     * Subclasses should overload this method to provide any code that 
     * changes the appearance of the widget.
     * </p>
     */
    protected abstract void updateControl();
    
    /**
     * 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(theControl.getDisplay(), privateInterface);
        }
    }
    
}