/*******************************************************************************
 * Copyright (c) 2005, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.ui.internal;

import org.eclipse.core.runtime.Assert;
import org.eclipse.jface.action.IAction;
import org.eclipse.ui.IPageListener;
import org.eclipse.ui.IPerspectiveDescriptor;
import org.eclipse.ui.IWorkbenchPage;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.PerspectiveAdapter;

/**
 * Utility class for tracking the active perspective in a window.
 *
 * @since 3.1
 */
public class PerspectiveTracker extends PerspectiveAdapter implements IPageListener {

	private IWorkbenchWindow window;

	private IAction action;

	/**
	 * Creates a perspective tracker for the given window. Subclasses should
	 * override <code>update(IPerspectiveDescriptor)</code> to get notified of
	 * perspective changes.
	 *
	 * @param window the window to track
	 */
	protected PerspectiveTracker(IWorkbenchWindow window) {
		Assert.isNotNull(window);
		this.window = window;
		window.addPageListener(this);
		window.addPerspectiveListener(this);
	}

	/**
	 * Creates a perspective tracker for the given window which will enable the
	 * given action only when there is an active perspective.
	 *
	 * @param window the window to track
	 * @param action the action to enable or disable
	 */
	public PerspectiveTracker(IWorkbenchWindow window, IAction action) {
		this(window);
		this.action = action;
		update();
	}

	/**
	 * Disposes the tracker.
	 */
	public void dispose() {
		if (window != null) {
			window.removePageListener(this);
			window.removePerspectiveListener(this);
			window = null;
		}
	}

	@Override
	public void pageActivated(IWorkbenchPage page) {
		update();
	}

	@Override
	public void pageClosed(IWorkbenchPage page) {
		update();
	}

	@Override
	public void pageOpened(IWorkbenchPage page) {
		// ignore
	}

	@Override
	public void perspectiveActivated(IWorkbenchPage page, IPerspectiveDescriptor perspective) {
		update();
	}

	/**
	 * Determines the active perspective in the window and calls
	 * <code>update(IPerspectiveDescriptor)</code>.
	 */
	private void update() {
		if (window != null) {
			IPerspectiveDescriptor persp = null;
			IWorkbenchPage page = window.getActivePage();
			if (page != null) {
				persp = page.getPerspective();
			}
			update(persp);
		}
	}

	/**
	 * Performs some function based on the active perspective in the window.
	 * <p>
	 * The default implementation enables the action (if given) if there is an
	 * active perspective, otherwise it disables it.
	 * </p>
	 * <p>
	 * Subclasses may override or extend.
	 * </p>
	 *
	 * @param persp the active perspective in the window, or <code>null</code> if
	 *              none
	 */
	protected void update(IPerspectiveDescriptor persp) {
		if (action != null) {
			action.setEnabled(persp != null);
		}
	}

}
