/**
 * <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: BasicCommandStack.java,v 1.3 2005/06/06 05:36:11 david_williams Exp $
 */
package org.eclipse.emf.common.command;


import java.util.ArrayList;
import java.util.Collection;
import java.util.EventObject;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

import org.eclipse.wst.sse.core.internal.Logger;


/**
 * A basic and obvious implementation of an undoable stack of commands. See
 * {@link Command} for more details about the command methods that this
 * implementation uses.
 */
public class BasicCommandStack implements CommandStack {
	/**
	 * The list of commands.
	 */
	protected List commandList;

	/**
	 * The current position within the list from which the next execute, undo,
	 * or redo, will be performed.
	 */
	protected int top;

	/**
	 * The command most recently executed, undone, or redone.
	 */
	protected Command mostRecentCommand;

	/**
	 * The {@link CommandStackListener}s.
	 */
	protected Collection listeners;

	/**
	 * The value of {@link #top} when {@link #saveIsDone} is called.
	 */
	protected int saveIndex = -1;

	/**
	 * Creates a new empty instance.
	 */
	public BasicCommandStack() {
		commandList = new ArrayList();
		top = -1;
		listeners = new ArrayList();
	}

	/*
	 * Javadoc copied from interface.
	 */
	public void execute(Command command) {
		// If the command is executable, record and execute it.
		//
		if (command != null && command.canExecute()) {
			// Clear the list past the top.
			//
			for (ListIterator commands = commandList.listIterator(top + 1); commands.hasNext(); commands.remove()) {
				Command otherCommand = (Command) commands.next();
				otherCommand.dispose();
			}

			try {
				command.execute();
				mostRecentCommand = command;
				commandList.add(command);
				++top;
			}
			catch (RuntimeException exception) {
				handleError(exception);

				mostRecentCommand = null;
				command.dispose();
			}

			// This is kind of tricky.
			// If the saveIndex was in the redo part of the command list which
			// has now been wiped out,
			// then we can never reach a point where a save is not necessary,
			// not even if we undo all the way back to the beginning.
			//
			if (saveIndex >= top) {
				// This forces isSaveNeded to always be true.
				//
				saveIndex = -2;
			}

			notifyListeners();
		}
		else {
			command.dispose();
		}
	}

	/*
	 * Javadoc copied from interface.
	 */
	public boolean canUndo() {
		return top != -1 && ((Command) commandList.get(top)).canUndo();
	}

	/*
	 * Javadoc copied from interface.
	 */
	public void undo() {
		if (canUndo()) {
			Command command = (Command) commandList.get(top--);
			try {
				command.undo();
				mostRecentCommand = command;
			}
			catch (RuntimeException exception) {
				handleError(exception);

				mostRecentCommand = null;
				flush();
			}

			notifyListeners();
		}
	}

	/*
	 * Javadoc copied from interface.
	 */
	public boolean canRedo() {
		return top < commandList.size() - 1;
	}

	/*
	 * Javadoc copied from interface.
	 */
	public void redo() {
		if (canRedo()) {
			Command command = (Command) commandList.get(++top);
			try {
				command.redo();
				mostRecentCommand = command;
			}
			catch (RuntimeException exception) {
				handleError(exception);

				mostRecentCommand = null;

				// Clear the list past the top.
				//
				for (ListIterator commands = commandList.listIterator(top--); commands.hasNext(); commands.remove()) {
					Command otherCommand = (Command) commands.next();
					otherCommand.dispose();
				}
			}

			notifyListeners();
		}
	}

	/*
	 * Javadoc copied from interface.
	 */
	public void flush() {
		// Clear the list.
		//
		for (ListIterator commands = commandList.listIterator(); commands.hasNext(); commands.remove()) {
			Command command = (Command) commands.next();
			command.dispose();
		}
		commandList.clear();
		top = -1;
		saveIndex = -1;
		notifyListeners();
		mostRecentCommand = null;
	}

	/*
	 * Javadoc copied from interface.
	 */
	public Command getUndoCommand() {
		return top == -1 || top == commandList.size() ? null : (Command) commandList.get(top);
	}

	/*
	 * Javadoc copied from interface.
	 */
	public Command getRedoCommand() {
		return top + 1 >= commandList.size() ? null : (Command) commandList.get(top + 1);
	}

	/*
	 * Javadoc copied from interface.
	 */
	public Command getMostRecentCommand() {
		return mostRecentCommand;
	}

	/*
	 * Javadoc copied from interface.
	 */
	public void addCommandStackListener(CommandStackListener listener) {
		listeners.add(listener);
	}

	/*
	 * Javadoc copied from interface.
	 */
	public void removeCommandStackListener(CommandStackListener listener) {
		listeners.remove(listener);
	}

	/**
	 * This is called to ensure that
	 * {@link CommandStackListener#commandStackChanged} is called for each
	 * listener.
	 */
	protected void notifyListeners() {
		for (Iterator i = listeners.iterator(); i.hasNext();) {
			((CommandStackListener) i.next()).commandStackChanged(new EventObject(this));
		}
	}

	/**
	 * Handles an exception thrown during command execution by loging it with
	 * the plugin.
	 */
	protected void handleError(Exception exception) {
		Logger.logException(UnDoCommonMessages._UI_IgnoreException_exception, exception);
	}

	/**
	 * Called after a save has been successfully performed.
	 */
	public void saveIsDone() {
		// Remember where we are now.
		//
		saveIndex = top;
	}

	/**
	 * Returns whether the model has changes since {@link #saveIsDone} was
	 * call the last.
	 * 
	 * @return whether the model has changes since <code>saveIsDone</code>
	 *         was call the last.
	 */
	public boolean isSaveNeeded() {
		// Only if we are at the remembered index do we NOT need to save.
		//
		// return top != saveIndex;

		if (saveIndex < -1) {
			return true;
		}

		if (top > saveIndex) {
			for (int i = top; i > saveIndex; --i) {
				if (!(commandList.get(i) instanceof AbstractCommand.NonDirtying)) {
					return true;
				}
			}
		}
		else {
			for (int i = saveIndex; i > top; --i) {
				if (!(commandList.get(i) instanceof AbstractCommand.NonDirtying)) {
					return true;
				}
			}
		}

		return false;
	}
}