/*******************************************************************************
 * Copyright (c) 2003, 2005 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.commands;

import java.util.Map;

/**
 * A handler is the pluggable piece of a command that handles execution. Each
 * command can have zero or more handlers associated with it (in general), of
 * which only one will be active at any given moment in time. When the command
 * is asked to execute, it will simply pass that request on to its active
 * handler, if any.
 * <p>
 * This interface is not intended to be extended by clients.
 * </p>
 * 
 * @since 3.0
 * @deprecated Please use the "org.eclipse.core.commands" plug-in instead.
 * @see org.eclipse.core.commands.IHandler
 */
public interface IHandler {

    /**
     * Registers an instance of <code>IHandlerListener</code> to listen for
     * changes to properties of this instance.
     * 
     * @param handlerListener
     *            the instance to register. Must not be <code>null</code>. If
     *            an attempt is made to register an instance which is already
     *            registered with this instance, no operation is performed.
     */
    void addHandlerListener(IHandlerListener handlerListener);

    /**
     * Disposes of this handler. This method is run once when the object is no
     * longer referenced. This can be used as an opportunity to unhook listeners
     * from other objects.
     */
    public void dispose();

    /**
     * Executes with the map of parameter values by name.
     * 
     * @param parameterValuesByName
     *            the map of parameter values by name. Reserved for future use,
     *            must be <code>null</code>.
     * @return the result of the execution. Reserved for future use, must be
     *         <code>null</code>.
     * @throws ExecutionException
     *             if an exception occurred during execution.
     */
    Object execute(Map parameterValuesByName) throws ExecutionException;

    /**
     * Returns the map of attribute values by name.
     * <p>
     * Notification is sent to all registered listeners if this property
     * changes.
     * </p>
     * 
     * @return the map of attribute values by name. This map may be empty, but
     *         is guaranteed not to be <code>null</code>. If this map is not
     *         empty, its collection of keys is guaranteed to only contain
     *         instances of <code>String</code>.
     */
    Map getAttributeValuesByName();

    /**
     * Unregisters an instance of <code>IPropertyListener</code> listening for
     * changes to properties of this instance.
     * 
     * @param handlerListener
     *            the instance to unregister. Must not be <code>null</code>.
     *            If an attempt is made to unregister an instance which is not
     *            already registered with this instance, no operation is
     *            performed.
     */
    void removeHandlerListener(IHandlerListener handlerListener);
}