/*******************************************************************************
 * 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;

import org.eclipse.jface.action.IAction;
import org.eclipse.jface.viewers.ISelection;

/**
 * Interface for actions contributed via an extension point.
 * <p>
 * This interface should be implemented by clients who need to contribute
 * actions via an extension point. The workbench will generate a <b>proxy
 * action</b> object on behalf of the plug-in to avoid having to activate the
 * plug-in until the user needs it. If the action is performed the workbench
 * will load the class that implements this interface and create what is called
 * an <b>action delegate</b> object. Then the request, and all subsequent ones,
 * are forwarded through the proxy action to the action delegate, which does the
 * real work.
 * </p>
 * <p>
 * The proxy action is the one that appears in the UI, so the action delegate
 * will need to talk to the proxy action in order to keep up an appropriate
 * appearance. Once the action delegate has been created, it will be notified of
 * all selection changes, allowing it to enable or disable the proxy action
 * appropriately.
 * </p>
 * <p>
 * An action delegate cannot be consulted about selection changes before the
 * action is performed because it does not exist. For this reason, control of
 * the action's enable state should also be exercised through simple XML rules
 * contained in the extension. These rules allow enable state control before the
 * action delegate's plug-in is loaded.
 * </p>
 * <p>
 * Clients can choose to subclass the provided abstract implementation
 * <code>org.eclipse.ui.actions.ActionDelegate</code> or implement the interface
 * directly.
 * </p>
 *
 * @see org.eclipse.ui.actions.ActionDelegate
 * @see org.eclipse.ui.IActionDelegate2
 */
public interface IActionDelegate {
	/**
	 * Performs this action.
	 * <p>
	 * This method is called by the proxy action when the action has been triggered.
	 * Implement this method to do the actual work.
	 * </p>
	 * <p>
	 * <b>Note:</b> If the action delegate also implements
	 * <code>IActionDelegate2</code>, then this method is not invoked but instead
	 * the <code>runWithEvent(IAction, Event)</code> method is called.
	 * </p>
	 *
	 * @param action the action proxy that handles the presentation portion of the
	 *               action
	 */
	void run(IAction action);

	/**
	 * Notifies this action delegate that the selection in the workbench has
	 * changed.
	 * <p>
	 * Implementers can use this opportunity to change the availability of the
	 * action or to modify other presentation properties.
	 * </p>
	 * <p>
	 * When the selection changes, the action enablement state is updated based on
	 * the criteria specified in the plugin.xml file. Then the delegate is notified
	 * of the selection change regardless of whether the enablement criteria in the
	 * plugin.xml file is met.
	 * </p>
	 *
	 * @param action    the action proxy that handles presentation portion of the
	 *                  action
	 * @param selection the current selection, or <code>null</code> if there is no
	 *                  selection.
	 */
	void selectionChanged(IAction action, ISelection selection);
}