/*******************************************************************************
 * Copyright (c) 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
 * Port to the D programming language:
 *     Frank Benoit <benoit@tionex.de>
 *******************************************************************************/
module org.eclipse.core.commands.operations.OperationHistoryFactory;

import org.eclipse.core.commands.operations.IOperationHistory;
import org.eclipse.core.commands.operations.DefaultOperationHistory;

import java.lang.all;

/**
 * <p>
 * This class is used to maintain the instance of the operation history that
 * should be used by classes that access the undo or redo history and add
 * undoable operations to the history.
 *
 * <p>
 * It is intended that an application can create an operation history appropriate
 * for its needs and set it into this class.  Otherwise, a default operation history
 * will be created.  The operation history may only be set one time.  All classes that
 * access an operations history use this class to obtain the correct instance.
 *
 * @since 3.1
 */
public final class OperationHistoryFactory {

    private static IOperationHistory operationHistory;

    /**
     * Return the operation history to be used for managing undoable operations.
     *
     * @return the operation history to be used for executing, undoing, and
     *         redoing operations.
     */
    public static IOperationHistory getOperationHistory() {
        if (operationHistory is null) {
            operationHistory = new DefaultOperationHistory();
        }
        return operationHistory;
    }

    /**
     * Set the operation history to be used for managing undoable operations.
     * This method may only be called one time, and must be called before any
     * request to get the history.  Attempts to set the operation history will
     * be ignored after it has been already set, or after a default one has
     * been created.
     *
     * @param history
     *            the operation history to be used for executing, undoing, and
     *            redoing operations.
     */
    public static void setOperationHistory(IOperationHistory history) {
        // If one has already been set or created, ignore this request.
        if (operationHistory is null) {
            operationHistory = history;
        }
    }

    private this() {
        // may not be instantiated
    }

}