/*******************************************************************************

 * Copyright (c) 2009 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

 ******************************************************************************/

package org.eclipse.core.databinding;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

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.list.IListChangeListener;

import org.eclipse.core.databinding.observable.list.IObservableList;

import org.eclipse.core.databinding.observable.list.ListChangeEvent;

import org.eclipse.core.databinding.observable.list.ListDiff;

import org.eclipse.core.databinding.observable.list.ListDiffEntry;

/**

 * A TargetListener listens to changes of any target of any

 * ValidationStatusProvider in the given context.

 * 

 * @since 1.2

 * 

 */

public class TargetsListener {

	/**

	 * Creates a TargetsListener. Once when any target changes the listener will

	 * be notified and the TargetsListener will be disposed.

	 * 

	 * @param context

	 * @param listener

	 * @return The TargetsListener is returned so it can be disposed even if no

	 *         change occurs. It should not be used for anything else.

	 */

	public static TargetsListener listenOnce(DataBindingContext context, final IChangeListener listener) {

		final TargetsListener targetsListener = new TargetsListener(context);

		targetsListener.addChangeListener(new IChangeListener() {

			public void handleChange(ChangeEvent event) {

				listener.handleChange(event);

				targetsListener.dispose();

			}

		});

		return targetsListener;

	}

	private final List changeListeners = new ArrayList();

	private IChangeListener targetListener = new IChangeListener() {

		public void handleChange(ChangeEvent event) {

			Iterator iterator = changeListeners.iterator();

			while (iterator.hasNext()) {

				IChangeListener listener = (IChangeListener) iterator.next();

				listener.handleChange(event);

			}

		}

	};

	private IListChangeListener validationStatusProviderTargetsListener = new IListChangeListener() {

		public void handleListChange(ListChangeEvent event) {

			ListDiff diff = event.diff;

			ListDiffEntry[] differences = diff.getDifferences();

			for (int i = 0; i < differences.length; i++) {

				ListDiffEntry listDiffEntry = differences[i];

				IObservable target = (IObservable) listDiffEntry.getElement();

				if (listDiffEntry.isAddition()) {

					target.addChangeListener(targetListener);

				} else {

					target.removeChangeListener(targetListener);

				}

			}

		}

	};

	private IObservableList targets;

	/**

	 * A TargetListener listens to changes of any target of any

	 * ValidationStatusProvider in the given context.

	 * 

	 * @param context

	 */

	public TargetsListener(DataBindingContext context) {

		targets = BindingProperties.validationStatusProviders().lists(

				   BindingProperties.targets()).observe(context);

		targets.addListChangeListener(validationStatusProviderTargetsListener);

		for (Iterator it = targets.iterator(); it.hasNext();) {

			((IObservable) it.next()).addChangeListener(targetListener);

		}

	}

	/**

	 * Adds the {@link IChangeListener} to the list of target listeners.

	 * 

	 * @param listener

	 *            The IChangeListener that will be notified in case any target

	 *            changes.

	 * @since 1.2

	 */

	public final void addChangeListener(IChangeListener listener) {

		changeListeners.add(listener);

	}

	/**

	 * Removes the {@link IChangeListener} from the list of target listeners.

	 * 

	 * @param listener

	 *            The IChangeListener that should no longer be notified in case

	 *            any target changes.

	 * @since 1.2

	 */

	public final void removeChangeListener(IChangeListener listener) {

		changeListeners.remove(listener);

	}

	/**

	 * 

	 */

	public void dispose() {

		for (Iterator it = targets.iterator(); it.hasNext();) {

			((IObservable) it.next()).removeChangeListener(targetListener);

		}

		targets.dispose();

	}

}

	private TargetsListener targetsListener;