/*
 * 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.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;

import org.opends.sdk.*;
import org.opends.sdk.responses.Responses;
import org.opends.sdk.responses.Result;



/**
 * This class provides a skeletal implementation of the {@code
 * FutureResult} interface, to minimize the effort required to implement
 * this interface.
 * <p>
 * This {@code FutureResult} implementation provides the following
 * features:
 * <ul>
 * <li>The {@link #get} methods throw {@link ErrorResultException}s
 * instead of the more generic {@code ExecutionException}s.
 * <li>The {@link #get} methods never throw {@code
 * CancellationException} since requests in this SDK can usually be
 * cancelled via other external means (e.g. the {@code Cancel} extended
 * operation) for which there are well defined error results. Therefore
 * cancellation is always signalled by throwing a
 * {@link CancelledResultException} in order to be consistent with other
 * error results.
 * <li>A {@link ResultHandler} can be provided to the constructor. The
 * result handler will be invoked immediately after the result or error
 * is received but before threads blocked on {@link #get} are released.
 * More specifically, result handler invocation <i>happens-before</i> a
 * call to {@link #get}. <b>NOTE:</b> a result handler which attempts to
 * call {@link #get} will deadlock.
 * <li>Sub-classes may choose to implement specific cancellation cleanup
 * by implementing the {@link #handleCancelRequest} method.
 * </ul>
 *
 * @param <M>
 *          The type of result returned by this completion future.
 */
public abstract class AbstractFutureResult<M> implements
    FutureResult<M>, ResultHandler<M>
{
  @SuppressWarnings("serial")
  private final class Sync extends AbstractQueuedSynchronizer
  {
    // State value representing the initial state before a result has
    // been received.
    private static final int WAITING = 0;

    // State value representing that a result has been received and is
    // being processed.
    private static final int PENDING = 1;

    // State value representing that the request was cancelled.
    private static final int CANCELLED = 2;

    // State value representing that the request has failed.
    private static final int FAIL = 3;

    // State value representing that the request has succeeded.
    private static final int SUCCESS = 4;

    // These do not need to be volatile since their values are published
    // by updating the state after they are set and reading the state
    // immediately before they are read.
    private ErrorResultException errorResult = null;

    private M result = null;



    private M get0() throws ErrorResultException
    {
      if (errorResult != null)
      {
        // State must be FAILED or CANCELLED.
        throw errorResult;
      }
      else
      {
        // State must be SUCCESS.
        return result;
      }
    }



    private boolean setStatePending()
    {
      for (;;)
      {
        final int s = getState();
        if (s != WAITING)
        {
          return false;
        }
        if (compareAndSetState(s, PENDING))
        {
          return true;
        }
      }
    }



    /**
     * Allow all threads to acquire if future has completed.
     */
    protected int tryAcquireShared(int ignore)
    {
      return innerIsDone() ? 1 : -1;
    }



    /**
     * Signal that the future has completed and threads waiting on get()
     * can be released.
     */
    protected boolean tryReleaseShared(int finalState)
    {
      // Ensures that errorResult/result is published.
      setState(finalState);
      return true;
    }



    boolean innerCancel(boolean mayInterruptIfRunning)
    {
      if (!setStatePending())
      {
        return false;
      }

      // Perform implementation defined cancellation.
      ErrorResultException errorResult = handleCancelRequest(mayInterruptIfRunning);
      if (errorResult == null)
      {
        final Result result = Responses
            .newResult(ResultCode.CLIENT_SIDE_USER_CANCELLED);
        errorResult = ErrorResultException.wrap(result);
      }
      this.errorResult = errorResult;

      try
      {
        // Invoke error result completion handler.
        if (handler != null)
        {
          handler.handleErrorResult(errorResult);
        }
      }
      finally
      {
        releaseShared(CANCELLED); // Publishes errorResult.
      }

      return true;
    }



    M innerGet() throws ErrorResultException, InterruptedException
    {
      acquireSharedInterruptibly(0);
      return get0();
    }



    M innerGet(long nanosTimeout) throws ErrorResultException,
        TimeoutException, InterruptedException
    {
      if (!tryAcquireSharedNanos(0, nanosTimeout))
      {
        throw new TimeoutException();
      }
      else
      {
        return get0();
      }
    }



    boolean innerIsCancelled()
    {
      return getState() == CANCELLED;
    }



    boolean innerIsDone()
    {
      return getState() > 1;
    }



    void innerSetErrorResult(ErrorResultException errorResult)
    {
      if (setStatePending())
      {
        this.errorResult = errorResult;

        try
        {
          // Invoke error result completion handler.
          if (handler != null)
          {
            handler.handleErrorResult(errorResult);
          }
        }
        finally
        {
          releaseShared(FAIL); // Publishes errorResult.
        }
      }
    }



    void innerSetResult(M result)
    {
      if (setStatePending())
      {
        this.result = result;

        try
        {
          // Invoke result completion handler.
          if (handler != null)
          {
            handler.handleResult(result);
          }
        }
        finally
        {
          releaseShared(SUCCESS); // Publishes result.
        }
      }
    }
  }



  private final Sync sync = new Sync();

  private final ResultHandler<? super M> handler;



  /**
   * Creates a new abstract future result with the provided result
   * handler.
   *
   * @param handler
   *          A result handler which will be forwarded the result or
   *          error when it arrives.
   */
  protected AbstractFutureResult(ResultHandler<? super M> handler)
  {
    this.handler = handler;
  }



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



  /**
   * {@inheritDoc}
   */
  public final M get() throws ErrorResultException,
      InterruptedException
  {
    return sync.innerGet();
  }



  /**
   * {@inheritDoc}
   */
  public final M get(long timeout, TimeUnit unit)
      throws ErrorResultException, TimeoutException,
      InterruptedException
  {
    return sync.innerGet(unit.toNanos(timeout));
  }



  /**
   * Sets the error result associated with this future. If ({@code
   * isDone() == true}) then the error result will be ignored, otherwise
   * the result handler will be invoked if one was provided and, on
   * return, any threads waiting on {@link #get} will be released and
   * the provided error result will be thrown.
   *
   * @param errorResult
   *          The error result.
   */
  public final void handleErrorResult(ErrorResultException errorResult)
  {
    sync.innerSetErrorResult(errorResult);
  }



  /**
   * Sets the result associated with this future. If ({@code isDone() ==
   * true}) then the result will be ignored, otherwise the result
   * handler will be invoked if one was provided and, on return, any
   * threads waiting on {@link #get} will be released and the provided
   * result will be returned.
   *
   * @param result
   *          The result.
   */
  public final void handleResult(M result)
  {
    sync.innerSetResult(result);
  }



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



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



  /**
   * Invoked when {@link #cancel} is called and {@code isDone() ==
   * false} and immediately before any threads waiting on {@link #get}
   * are released. Implementations may choose to return a custom error
   * result if needed or return {@code null} if the following default
   * error result is acceptable:
   *
   * <pre>
   * Result result = Responses
   *     .newResult(ResultCode.CLIENT_SIDE_USER_CANCELLED);
   * </pre>
   *
   * In addition, implementations may perform other cleanup, for
   * example, by issuing an LDAP abandon request. The default
   * implementation is to do nothing.
   *
   * @param mayInterruptIfRunning
   *          {@code true} if the thread executing executing the
   *          response handler should be interrupted; otherwise,
   *          in-progress response handlers are allowed to complete.
   * @return The custom error result, or {@code null} if the default is
   *         acceptable.
   */
  protected ErrorResultException handleCancelRequest(
      boolean mayInterruptIfRunning)
  {
    // Do nothing by default.
    return null;
  }

}