/*******************************************************************************
 * Copyright (c) 2000, 2004 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.ui.actions;

import org.eclipse.jface.action.Action;
import org.eclipse.ui.IPartListener;
import org.eclipse.ui.IWorkbenchPart;

/**
 * The abstract superclass for actions that listen to part activation and
 * open/close events. This implementation tracks the active part (see 
 * <code>getActivePart</code>) and provides a convenient place to monitor
 * part lifecycle events that could affect the availability of the action.
 * <p>
 * Subclasses must implement the following <code>IAction</code> method:
 * <ul>
 *   <li><code>run</code> - to do the action's work</li>
 * </ul>
 * </p>
 * <p>
 * Subclasses may extend any of the <code>IPartListener</code> methods if the
 * action availablity needs to be recalculated:
 * <ul>
 *   <li><code>partActivated</code></li> 
 *   <li><code>partDeactivated</code></li>
 *   <li><code>partOpened</code></li>
 *   <li><code>partClosed</code></li>
 *   <li><code>partBroughtToTop</code></li>
 * </ul>
 * </p>
 * <p>
 * Although this method implements the <code>IPartListener</code> interface,
 * it does NOT register itself. 
 * </p>
 */
public abstract class PartEventAction extends Action implements IPartListener {

    /**
     * The active part, or <code>null</code> if none.
     */
    private IWorkbenchPart activePart;

    /**
     * Creates a new action with the given text.
     *
     * @param text the action's text, or <code>null</code> if there is no text
     */
    protected PartEventAction(String text) {
        super(text);
    }

    /**
     * Creates a new action with the given text and style.
     *
     * @param text the action's text, or <code>null</code> if there is no text
     * @param style one of <code>AS_PUSH_BUTTON</code>, <code>AS_CHECK_BOX</code>,
     * 		<code>AS_DROP_DOWN_MENU</code>, <code>AS_RADIO_BUTTON</code>, and
     * 		<code>AS_UNSPECIFIED</code>
     * @since 3.0
     */
    protected PartEventAction(String text, int style) {
        super(text, style);
    }

    /**
     * Returns the currently active part in the workbench.
     *
     * @return currently active part in the workbench, or <code>null</code> if none
     */
    public IWorkbenchPart getActivePart() {
        return activePart;
    }

    /**
     * The <code>PartEventAction</code> implementation of this 
     * <code>IPartListener</code> method records that the given part is active.
     * Subclasses may extend this method if action availability has to be
     * recalculated.
     */
    public void partActivated(IWorkbenchPart part) {
        activePart = part;
    }

    /**
     * The <code>PartEventAction</code> implementation of this 
     * <code>IPartListener</code> method does nothing. Subclasses should extend
     * this method if action availability has to be recalculated.
     */
    public void partBroughtToTop(IWorkbenchPart part) {
        // do nothing
    }

    /**
     * The <code>PartEventAction</code> implementation of this 
     * <code>IPartListener</code> method clears the active part if it just closed.
     * Subclasses may extend this method if action availability has to be
     * recalculated.
     */
    public void partClosed(IWorkbenchPart part) {
        if (part == activePart)
            activePart = null;
    }

    /**
     * The <code>PartEventAction</code> implementation of this 
     * <code>IPartListener</code> method records that there is no active part.
     * Subclasses may extend this method if action availability has to be
     * recalculated.
     */
    public void partDeactivated(IWorkbenchPart part) {
        activePart = null;
    }

    /**
     * The <code>PartEventAction</code> implementation of this 
     * <code>IPartListener</code> method does nothing. Subclasses should extend
     * this method if action availability has to be recalculated.
     */
    public void partOpened(IWorkbenchPart part) {
        // do nothing
    }
}
