/*******************************************************************************
 * Copyright (c) 2000, 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.navigator.framelist;

import org.eclipse.osgi.util.NLS;
import org.eclipse.ui.ISharedImages;
import org.eclipse.ui.PlatformUI;

/**
 * Generic "Back" action which goes back one frame,
 * @since 3.4
 */
public class BackAction extends FrameAction {

	private static final String ID = "org.eclipse.ui.framelist.back"; //$NON-NLS-1$

	/**
	 * Constructs a new action for the specified frame list.
	 *
	 * @param frameList the frame list
	 */
	public BackAction(FrameList frameList) {
		super(frameList);
		setId(ID);
		setText(FrameListMessages.Back_text);
		ISharedImages images = PlatformUI.getWorkbench().getSharedImages();
		setImageDescriptor(images
				.getImageDescriptor(ISharedImages.IMG_TOOL_BACK));
		setDisabledImageDescriptor(images
				.getImageDescriptor(ISharedImages.IMG_TOOL_BACK_DISABLED));
		PlatformUI.getWorkbench().getHelpSystem().setHelp(this,
				IFrameListHelpContextIds.BACK_ACTION);
		update();
	}

	private Frame getPreviousFrame() {
		FrameList list = getFrameList();
		return list.getFrame(list.getCurrentIndex() - 1);
	}

	private String getToolTipText(Frame previousFrame) {
		if (previousFrame != null) {
			String text = previousFrame.getToolTipText();
			if (text != null && text.length() > 0) {
				return NLS.bind(FrameListMessages.Back_toolTipOneArg, text);
			}
		}
		return FrameListMessages.Back_toolTip;
	}

	/**
	 * Calls <code>back()</code> on the frame list.
	 */
	@Override
	public void run() {
		getFrameList().back();
	}

	/**
	 * Updates this action's enabled state and tool tip text.
	 * This action is enabled only when there is a previous frame in the frame list.
	 * The tool tip text is "Back to " plus the tool tip text for the previous frame.
	 */
	@Override
	public void update() {
		super.update();
		Frame previousFrame = getPreviousFrame();
		setEnabled(previousFrame != null);
		setToolTipText(getToolTipText(previousFrame));
	}

}
