/*******************************************************************************
 * Copyright (c) 2007, 2008 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:
 *     Boris Bokowski, IBM Corporation - initial API and implementation
 *     Matthew Hall - bug 212468
 *******************************************************************************/
module org.eclipse.core.internal.databinding.observable.StalenessObservableValue;

import java.lang.all;

import org.eclipse.core.databinding.observable.ChangeEvent;
import org.eclipse.core.databinding.observable.Diffs;
import org.eclipse.core.databinding.observable.IChangeListener;
import org.eclipse.core.databinding.observable.IObservable;
import org.eclipse.core.databinding.observable.IStaleListener;
import org.eclipse.core.databinding.observable.StaleEvent;
import org.eclipse.core.databinding.observable.value.AbstractObservableValue;

/**
 * An observable value that tracks the staleness of an {@link IObservable}.
 * 
 * @since 1.1
 */
public class StalenessObservableValue : AbstractObservableValue {

    private class MyListener : IChangeListener, IStaleListener {
        public void handleChange(ChangeEvent event) {
            if (stale && !event.getObservable().isStale()) {
                stale = false;
                fireValueChange(Diffs.createValueDiff(Boolean.TRUE,
                        Boolean.FALSE));
            }
        }

        public void handleStale(StaleEvent staleEvent) {
            if (!stale) {
                stale = true;
                fireValueChange(Diffs.createValueDiff(Boolean.FALSE,
                        Boolean.TRUE));
            }
        }
    }

    private IObservable tracked;
    private bool stale;
    private MyListener listener = new MyListener();

    /**
     * Constructs a StalenessObservableValue that tracks the staleness of the
     * given {@link IObservable}.
     * 
     * @param observable
     *            the observable to track
     */
    public this(IObservable observable) {
        super(observable.getRealm());
        this.tracked = observable;
        this.stale = observable.isStale();
        tracked.addChangeListener(listener);
        tracked.addStaleListener(listener);
    }

    protected Object doGetValue() {
        return tracked.isStale() ? Boolean.TRUE : Boolean.FALSE;
    }

    public Object getValueType() {
        return Boolean.TYPE;
    }

    public synchronized void dispose() {
        if (tracked !is null) {
            tracked.removeChangeListener(listener);
            tracked.removeStaleListener(listener);
            tracked = null;
            listener = null;
        }
        super.dispose();
    }

}