/*******************************************************************************
 * 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.core.commands.contexts;

import java.util.Set;

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

/**
 * <p>
 * An event indicating that the set of defined context identifiers has changed.
 * </p>
 * 
 * @since 3.1
 * @see IContextManagerListener#contextManagerChanged(ContextManagerEvent)
 */
public final class ContextManagerEvent extends AbstractBitSetEvent {

	/**
	 * The bit used to represent whether the set of defined contexts has
	 * changed.
	 */
	private static final int CHANGED_CONTEXT_DEFINED = 1 << 1;

	/**
	 * The bit used to represent whether the set of active contexts has changed.
	 */
	private static final int CHANGED_CONTEXTS_ACTIVE = 1;

	/**
	 * The context identifier that was added or removed from the list of defined
	 * context identifiers.
	 */
	private final String contextId;

	/**
	 * The context manager that has changed.
	 */
	private final ContextManager contextManager;

	/**
	 * The set of context identifiers (strings) that were active before the
	 * change occurred. If the active contexts did not changed, then this value
	 * is <code>null</code>.
	 */
	private final Set previouslyActiveContextIds;

	/**
	 * Creates a new instance of this class.
	 * 
	 * @param contextManager
	 *            the instance of the interface that changed; must not be
	 *            <code>null</code>.
	 * @param contextId
	 *            The context identifier that was added or removed; may be
	 *            <code>null</code> if the active contexts are changing.
	 * @param contextIdAdded
	 *            Whether the context identifier became defined (otherwise, it
	 *            became undefined).
	 * @param activeContextsChanged
	 *            Whether the list of active contexts has changed.
	 * @param previouslyActiveContextIds
	 *            the set of identifiers of previously active contexts. This set
	 *            may be empty. If this set is not empty, it must only contain
	 *            instances of <code>String</code>. This set must be
	 *            <code>null</code> if activeContextChanged is
	 *            <code>false</code> and must not be null if
	 *            activeContextChanged is <code>true</code>.
	 */
	public ContextManagerEvent(final ContextManager contextManager,
			final String contextId, final boolean contextIdAdded,
			final boolean activeContextsChanged,
			final Set previouslyActiveContextIds) {
		if (contextManager == null) {
			throw new NullPointerException();
		}

		this.contextManager = contextManager;
		this.contextId = contextId;
		this.previouslyActiveContextIds = previouslyActiveContextIds;

		if (contextIdAdded) {
			changedValues |= CHANGED_CONTEXT_DEFINED;
		}
		if (activeContextsChanged) {
			changedValues |= CHANGED_CONTEXTS_ACTIVE;
		}
	}

	/**
	 * Returns the context identifier that was added or removed.
	 * 
	 * @return The context identifier that was added or removed. This value may
	 *         be <code>null</code> if no context identifier was added or
	 *         removed.
	 */
	public final String getContextId() {
		return contextId;
	}

	/**
	 * Returns the instance of the interface that changed.
	 * 
	 * @return the instance of the interface that changed. Guaranteed not to be
	 *         <code>null</code>.
	 */
	public final ContextManager getContextManager() {
		return contextManager;
	}

	/**
     * Returns the set of identifiers to previously active contexts.
     * 
     * @return the set of identifiers to previously active contexts. This set
     *         may be empty. If this set is not empty, it is guaranteed to only
     *         contain instances of <code>String</code>. This set is
     *         guaranteed to be <code>null</code> if
     *         haveActiveContextChanged() is <code>false</code> and is
     *         guaranteed to not be <code>null</code> if
     *         haveActiveContextsChanged() is <code>true</code>.
     */
	public final Set getPreviouslyActiveContextIds() {
		return previouslyActiveContextIds;
	}

	/**
	 * Returns whether the active context identifiers have changed.
	 * 
	 * @return <code>true</code> if the collection of active contexts changed;
	 *         <code>false</code> otherwise.
	 */
	public final boolean isActiveContextsChanged() {
		return ((changedValues & CHANGED_CONTEXTS_ACTIVE) != 0);
	}

	/**
	 * Returns whether the list of defined context identifiers has changed.
	 * 
	 * @return <code>true</code> if the list of context identifiers has
	 *         changed; <code>false</code> otherwise.
	 */
	public final boolean isContextChanged() {
		return (contextId != null);
	}

	/**
	 * Returns whether the context identifier became defined. Otherwise, the
	 * context identifier became undefined.
	 * 
	 * @return <code>true</code> if the context identifier became defined;
	 *         <code>false</code> if the context identifier became undefined.
	 */
	public final boolean isContextDefined() {
		return (((changedValues & CHANGED_CONTEXT_DEFINED) != 0) && (contextId != null));
	}
}