/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at
 * trunk/opends/resource/legal-notices/OpenDS.LICENSE
 * or https://OpenDS.dev.java.net/OpenDS.LICENSE.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at
 * trunk/opends/resource/legal-notices/OpenDS.LICENSE.  If applicable,
 * add the following below this CDDL HEADER, with the fields enclosed
 * by brackets "[]" replaced with your own identifying information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *
 *      Copyright 2009 Sun Microsystems, Inc.
 */

package com.sun.opends.sdk.util;



import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import org.opends.sdk.ErrorResultException;
import org.opends.sdk.FutureResult;
import org.opends.sdk.ResultHandler;



/**
 * An implementation of the {@code FutureResult} interface which can be
 * used to combine a sequence of two asynchronous operations into a
 * single future result. Implementations should override the methods
 * {@link #chainResult} and {@link #chainErrorResult} in order to define
 * the second asynchronous operation.
 *
 * @param <M>
 *          The type of the inner result.
 * @param <N>
 *          The type of the outer result.
 */
public abstract class RecursiveFutureResult<M, N> implements
    FutureResult<N>, ResultHandler<M>
{
  private final class FutureResultImpl extends AbstractFutureResult<N>
  {
    private FutureResultImpl(ResultHandler<? super N> handler)
    {
      super(handler);
    }



    public int getRequestID()
    {
      if (innerFuture instanceof FutureResult<?>)
      {
        FutureResult<?> tmp = (FutureResult<?>) innerFuture;
        return tmp.getRequestID();
      }
      else
      {
        return -1;
      }
    }



    /**
     * {@inheritDoc}
     */
    protected ErrorResultException handleCancelRequest(
        boolean mayInterruptIfRunning)
    {
      innerFuture.cancel(mayInterruptIfRunning);
      if (outerFuture != null)
      {
        outerFuture.cancel(mayInterruptIfRunning);
      }
      return null;
    }

  }



  private final FutureResultImpl impl;

  private volatile Future<?> innerFuture = null;

  // This does not need to be volatile since the inner future acts as a
  // memory barrier.
  private FutureResult<? extends N> outerFuture = null;



  /**
   * Creates a new asynchronous result chain which will chain an outer
   * asynchronous request once the inner asynchronous request completes.
   *
   * @param handler
   *          The outer result handler.
   */
  protected RecursiveFutureResult(ResultHandler<? super N> handler)
  {
    this.impl = new FutureResultImpl(handler);
  }



  /**
   * {@inheritDoc}
   */
  public final boolean cancel(boolean mayInterruptIfRunning)
  {
    return impl.cancel(mayInterruptIfRunning);
  }



  /**
   * {@inheritDoc}
   */
  public final N get() throws ErrorResultException,
      InterruptedException
  {
    return impl.get();
  }



  /**
   * {@inheritDoc}
   */
  public final N get(long timeout, TimeUnit unit)
      throws ErrorResultException, TimeoutException,
      InterruptedException
  {
    return impl.get(timeout, unit);
  }



  /**
   * {@inheritDoc}
   */
  public final int getRequestID()
  {
    return impl.getRequestID();
  }



  /**
   * {@inheritDoc}
   */
  public final void handleErrorResult(ErrorResultException error)
  {
    try
    {
      outerFuture = chainErrorResult(error, impl);
    }
    catch (final ErrorResultException e)
    {
      impl.handleErrorResult(e);
    }
  }



  /**
   * {@inheritDoc}
   */
  public final void handleResult(M result)
  {
    try
    {
      outerFuture = chainResult(result, impl);
    }
    catch (final ErrorResultException e)
    {
      impl.handleErrorResult(e);
    }
  }



  /**
   * {@inheritDoc}
   */
  public final boolean isCancelled()
  {
    return impl.isCancelled();
  }



  /**
   * {@inheritDoc}
   */
  public final boolean isDone()
  {
    return impl.isDone();
  }



  /**
   * Sets the inner future for this result chain. This must be done
   * before this future is published.
   *
   * @param future
   *          The inner future.
   */
  public final void setFutureResult(Future<?> future)
  {
    this.innerFuture = future;
  }



  /**
   * Invokes the outer request based on the error result of the inner
   * request and returns a future representing the result of the outer
   * request.
   * <p>
   * The default implementation is to terminate further processing by
   * re-throwing the inner error result.
   *
   * @param innerError
   *          The error result of the inner request.
   * @param handler
   *          The result handler to be used for the outer request.
   * @return A future representing the result of the outer request.
   * @throws ErrorResultException
   *           If the outer request could not be invoked and processing
   *           should terminate.
   */
  protected FutureResult<? extends N> chainErrorResult(
      ErrorResultException innerError, ResultHandler<? super N> handler)
      throws ErrorResultException
  {
    throw innerError;
  }



  /**
   * Invokes the outer request based on the result of the inner request
   * and returns a future representing the result of the outer request.
   *
   * @param innerResult
   *          The result of the inner request.
   * @param handler
   *          The result handler to be used for the outer request.
   * @return A future representing the result of the outer request.
   * @throws ErrorResultException
   *           If the outer request could not be invoked and processing
   *           should terminate.
   */
  protected abstract FutureResult<? extends N> chainResult(
      M innerResult, ResultHandler<? super N> handler)
      throws ErrorResultException;

}