/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions Copyright [year] [name of copyright owner]".
 *
 * Copyright 2006-2010 Sun Microsystems, Inc.
 * Portions Copyright 2015 ForgeRock AS.
 */
package org.opends.quicksetup.util;



/**
 * This class provides a mechanism for running a task in the background using a
 * separate thread and providing the caller with notification when it has
 * completed.
 * @param <T> type of object returned by this process
 */
public abstract class BackgroundTask<T>
{
  /**
   * Creates a new thread and begins running the task in the background.  When
   * the task has completed, the {@code backgroundTaskCompleted} method will be
   * invoked.
   */
  public final void startBackgroundTask()
  {
    BackgroundTaskThread<T> taskThread = new BackgroundTaskThread<>(this);
    taskThread.start();
  }



  /**
   * Performs all processing associated with the task.
   *
   * @return  An {@code Object} with information about the processing performed
   *          for this task, or {@code null} if no return value is needed.
   *
   * @throws Throwable throwable that will be passed through the method
   *          backgroundTaskCompleted.
   */
  public abstract T processBackgroundTask() throws Throwable;



  /**
   * This method will be invoked to indicate that the background task has
   * completed.  If processing completed successfully, then the
   * {@code Throwable} argument will be {@code null} and the {@code returnValue}
   * argument will contain the value returned by the
   * {@code processBackgroundTask} method.  If an exception or error was thrown,
   * then the {@code throwable} argument will not be {@code null}.
   *
   * @param  returnValue  The value returned by the
   *                      {@code processBackgroundTask} method when processing
   *                      completed, or {@code null} if no value was returned or
   *                      an exception was encountered during processing.
   * @param  throwable    A {@code Throwable} instance (e.g., an exception) that
   *                      was raised during processing, or {@code null} if all
   *                      processing completed successfully.
   */
  public abstract void backgroundTaskCompleted(T returnValue,
                                               Throwable throwable);
}