/*******************************************************************************
 * Copyright (c) 2004, 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.core.commands;

import org.eclipse.core.commands.common.AbstractBitSetEvent;

/**
 * An instance of this class describes changes to an instance of
 * <code>IHandler</code>.
 * <p>
 * This class is not intended to be extended by clients.
 * </p>
 * 
 * @since 3.1
 * @see IHandlerListener#handlerChanged(HandlerEvent)
 */
public final class HandlerEvent extends AbstractBitSetEvent {

	/**
	 * The bit used to represent whether the handler has changed its enabled
	 * state.
	 */
	private static final int CHANGED_ENABLED = 1;

	/**
	 * The bit used to represent whether the handler has changed its handled
	 * state.
	 */
	private static final int CHANGED_HANDLED = 1 << 1;

	/**
	 * The handler that changed; this value is never <code>null</code>.
	 */
	private final IHandler handler;

	/**
	 * Creates a new instance of this class.
	 * 
	 * @param handler
	 *            the instance of the interface that changed; must not be
     *            <code>null</code>.
	 * @param enabledChanged
	 *            Whether the enabled state of the handler has changed.
	 * @param handledChanged
	 *            Whether the handled state of the handler has changed.
	 */
	public HandlerEvent(final IHandler handler, final boolean enabledChanged,
			final boolean handledChanged) {
		if (handler == null) {
			throw new NullPointerException();
		}
		this.handler = handler;

		if (enabledChanged) {
			changedValues |= CHANGED_ENABLED;
		}
		if (handledChanged) {
			changedValues |= CHANGED_HANDLED;
		}
	}

	/**
	 * Returns the instance of the interface that changed.
	 * 
	 * @return the instance of the interface that changed. Guaranteed not to be
	 *         <code>null</code>.
	 */
	public IHandler getHandler() {
		return handler;
	}

	/**
	 * Returns whether or not the enabled property changed.
	 * 
	 * @return <code>true</code>, iff the enabled property changed.
	 */
	public boolean isEnabledChanged() {
		return ((changedValues & CHANGED_ENABLED) != 0);
	}

	/**
	 * Returns whether or not the handled property changed.
	 * 
	 * @return <code>true</code>, iff the handled property changed.
	 */
	public boolean isHandledChanged() {
		return ((changedValues & CHANGED_HANDLED) != 0);
	}
}
