/**
 * <copyright> 
 *
 * Copyright (c) 2002-2004 IBM Corporation and others.
 * All rights reserved.   This program and the accompanying materials
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors: 
 *   IBM - Initial API and implementation
 *
 * </copyright>
 *
 * $Id: IdentityCommand.java,v 1.3 2005/06/06 05:36:11 david_williams Exp $
 */
package org.eclipse.emf.common.command;


import java.util.Collection;
import java.util.Collections;


/**
 * A command that always produces the same result.
 */
public class IdentityCommand extends AbstractCommand {
	/**
	 * An empty instance of this object.
	 */
	public static final IdentityCommand INSTANCE = new IdentityCommand();

	/**
	 * Keeps track of the result returned from {@link #getResult}.
	 */
	protected Collection result;

	{
		// This ensures that these useless state variables at least reflect
		// the right value.
		//
		isPrepared = true;
		isExecutable = true;
	}

	/**
	 * Creates an empty instance.
	 */
	public IdentityCommand() {
		super();
		this.result = Collections.EMPTY_LIST;
	}

	/**
	 * Creates an instance with a result collection containing the given
	 * result object.
	 * 
	 * @param result
	 *            the one object in the result collection.
	 */
	public IdentityCommand(Object result) {
		super();
		this.result = Collections.singleton(result);
	}

	/**
	 * Creates an instance with the given result collection.
	 * 
	 * @param result
	 *            the result collection.
	 */
	public IdentityCommand(Collection result) {
		super();
		this.result = result;
	}

	/**
	 * Creates an instance with the given label.
	 * 
	 * @param label
	 *            the label.
	 */
	public IdentityCommand(String label) {
		this.label = label;
		this.result = Collections.EMPTY_LIST;
	}

	/**
	 * Creates an instance with the given label and a result collection
	 * containing the given result object.
	 * 
	 * @param label
	 *            the label.
	 * @param result
	 *            the one object in the result collection.
	 */
	public IdentityCommand(String label, Object result) {
		this.label = label;
		this.result = Collections.singleton(result);
	}

	/**
	 * Creates an instance with the given label the result collection.
	 * 
	 * @param label
	 *            the label.
	 * @param result
	 *            the result collection.
	 */
	public IdentityCommand(String label, Collection result) {
		this.label = label;
		this.result = result;
	}

	/**
	 * Creates an instance with the given label and description.
	 * 
	 * @param label
	 *            the label.
	 * @param description
	 *            the description.
	 */
	public IdentityCommand(String label, String description) {
		this.label = label;
		this.description = description;
		this.result = Collections.EMPTY_LIST;
	}

	/**
	 * Creates an instance with the given label, description, and a result
	 * collection containing the given result object.
	 * 
	 * @param label
	 *            the label.
	 * @param description
	 *            the description.
	 * @param result
	 *            the one object in the result collection.
	 */
	public IdentityCommand(String label, String description, Object result) {
		this.label = label;
		this.description = description;
		this.result = Collections.singleton(result);
	}

	/**
	 * Creates an instance with the given label, description, result
	 * collection.
	 * 
	 * @param label
	 *            the label.
	 * @param description
	 *            the description.
	 * @param result
	 *            the result collection.
	 */
	public IdentityCommand(String label, String description, Collection result) {
		this.label = label;
		this.description = description;
		this.result = result;
	}

	/**
	 * Returns <code>true</code>.
	 * 
	 * @return <code>true</code>.
	 */
	public boolean canExecute() {
		return true;
	}

	/**
	 * Do nothing.
	 */
	public void execute() {
	}

	/**
	 * Do nothing.
	 */
	public void undo() {
	}

	/**
	 * Do nothing.
	 */
	public void redo() {
	}

	/*
	 * Javadoc copied from base class.
	 */
	public String getLabel() {
		return label == null ? UnDoCommonMessages._UI_IdentityCommand_label : label;
	}

	/*
	 * Javadoc copied from base class.
	 */
	public String getDescription() {
		return description == null ? UnDoCommonMessages._UI_IdentityCommand_description : description;
	}

	/**
	 * Return the identity result.
	 * 
	 * @return the identity result.
	 */
	public Collection getResult() {
		return result;
	}
}