/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.drill.exec.util.concurrent;

import com.google.common.base.Preconditions;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/** Utility class to enhance the Java {@link ExecutorService} class functionality */
public final class ExecutorServiceUtil {

  /**
   * Helper method to submit the callabale task, gets the original future object, and wrap it
   * in another future object with the ability to decorate the {@link Future#cancel(boolean)} method;
   * this decorator will block when future cancellation is invoked (and the "mayInterruptIfRunning"
   * parameter is set to true).
   *
   * @param service the executor service
   * @param callable a callable task
   *
   * @return decorated future object upon successful submission
   * @see {@link ExecutorService#submit(Callable)
   */
  public static <T> Future<T> submit(ExecutorService service, Callable<T> callable) {
    // Wrap the original callable object
    CallableTaskWrapper<T> wrapper = new CallableTaskWrapper<T>(callable);
    // Submit the wrapper object and set the original future object within the wrapper
    wrapper.setFuture(service.submit(wrapper));

    return wrapper;
  }

  /** Executor task wrapper to enhance task cancellation behavior */
  public static final class CallableTaskWrapper<T> implements Callable<T>, Future<T> {
    /** Callable object */
    private final Callable<T> callableTask;
    /** Feature object returned after submission of the callback task */
    private volatile Future<T> future;
    /** Captures the callable task execution status */
    private volatile STATE state = STATE.NOT_RUNNING;
    /** Monitor object */
    private final Object monitor = new Object();

    /** Captures task's execution state */
    private enum STATE {
      NOT_RUNNING,
      RUNNING,
      DONE
    };

    /**
     * CTOR.
     * @param callableTask original callable task
     */
    public CallableTaskWrapper(Callable<T> callableTask) {
      this.callableTask = callableTask;
      Preconditions.checkNotNull(this.callableTask);
    }

    /** {@inheritDoc} */
    @Override
    public T call() throws Exception {
      try {
        state = STATE.RUNNING;

        return callableTask.call();
      } finally {
        state = STATE.DONE;

        // Optimization: no need to notify if the state is not "cancelled"
        if (isCancelled()) {
          synchronized (monitor) {
            monitor.notifyAll();
          }
        }
      }
    }

    /**
     * This method will block waiting if the callbale thread is still executing and the "mayInterruptIfRunning"
     * flag is set; this method will return when:
     * <ul>
     * <li>The callbale thread is done executing</li>
     * <li>The current thread got interrupted; no exception will be thrown and instead the interrupted flag will
     * be set</li>
     * </ul>
     *
     * @see {@link Future#cancel(boolean)}
     */
    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
      try {

        return future.cancel(mayInterruptIfRunning);
      } finally {
        // If this thread wishes immediate completion of the task and was interrupted (because it was still running),
        // then block this thread till the callable task is done executing.
        if (mayInterruptIfRunning) {
          waitTillDone();
        }
      }
    }

    /** {@inheritDoc} */
    @Override
    public boolean isCancelled() {
      // this method could be called from the call() API before the future is set
      return future != null && future.isCancelled();
    }

    /**
     * @return true if the task has completed execution
     */
    @Override
    public boolean isDone() {
      return state == STATE.DONE;
    }

    /** {@inheritDoc} */
    @Override
    public T get() throws InterruptedException, ExecutionException {
      return future.get();
    }

    /** {@inheritDoc} */
    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
      return future.get(timeout, unit);
    }

    /**
     * @param feature the feature to set
     */
    public void setFuture(Future<T> feature) {
      this.future = feature;
    }

    private void waitTillDone() {

      if (isRunning()) {
        // Save the current interrupted flag and clear it to allow wait operations
        boolean interrupted = Thread.interrupted();

        try {
          synchronized (monitor) {
            while (isRunning()) {
              try {
                monitor.wait();
              } catch (InterruptedException e) {
                interrupted = true;
              }
            }
          }
        } finally {
          if (interrupted) {
            Thread.currentThread().interrupt();
          }
        }
      }
    }

    private boolean isRunning() {
      return state == STATE.RUNNING;
    }
  }

// ----------------------------------------------------------------------------
// Local implementation
// ----------------------------------------------------------------------------

  /** Disabling object instantiation */
  private ExecutorServiceUtil() {

  }
}