/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 com.google.common.util.concurrent.testing;

import com.google.common.annotations.Beta;
import com.google.common.util.concurrent.ListenableFuture;

import junit.framework.TestCase;

import java.util.concurrent.CancellationException;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * Abstract test case parent for anything implementing {@link ListenableFuture}.
 * Tests the two get methods and the addListener method.
 *
 * @author Sven Mawson
 * @since 10.0
 */
@Beta
public abstract class AbstractListenableFutureTest extends TestCase {

  protected CountDownLatch latch;
  protected ListenableFuture<Boolean> future;

  @Override
  protected void setUp() throws Exception {

    // Create a latch and a future that waits on the latch.
    latch = new CountDownLatch(1);
    future = createListenableFuture(Boolean.TRUE, null, latch);
  }

  @Override
  protected void tearDown() throws Exception {

    // Make sure we have no waiting threads.
    latch.countDown();
  }

  /**
   * Constructs a listenable future with a value available after the latch
   * has counted down.
   */
  protected abstract <V> ListenableFuture<V> createListenableFuture(
      V value, Exception except, CountDownLatch waitOn);

  /**
   * Tests that the {@link Future#get()} method blocks until a value is
   * available.
   */
  public void testGetBlocksUntilValueAvailable() throws Throwable {

    assertFalse(future.isDone());
    assertFalse(future.isCancelled());

    final CountDownLatch successLatch = new CountDownLatch(1);
    final Throwable[] badness = new Throwable[1];

    // Wait on the future in a separate thread.
    new Thread(new Runnable() {
      @Override
      public void run() {
        try {
          assertSame(Boolean.TRUE, future.get());
          successLatch.countDown();
        } catch (Throwable t) {
          t.printStackTrace();
          badness[0] = t;
        }
      }}).start();

    // Release the future value.
    latch.countDown();

    assertTrue(successLatch.await(10, TimeUnit.SECONDS));

    if (badness[0] != null) {
      throw badness[0];
    }

    assertTrue(future.isDone());
    assertFalse(future.isCancelled());
  }

  /**
   * Tests that the {@link Future#get(long, TimeUnit)} method times out
   * correctly.
   */
  public void testTimeoutOnGetWorksCorrectly() throws InterruptedException,
      ExecutionException {

    // The task thread waits for the latch, so we expect a timeout here.
    try {
      future.get(20, TimeUnit.MILLISECONDS);
      fail("Should have timed out trying to get the value.");
    } catch (TimeoutException expected) {
      // Expected.
    } finally {
      latch.countDown();
    }
  }

  /**
   * Tests that a canceled future throws a cancellation exception.
   *
   * This method checks the cancel, isCancelled, and isDone methods.
   */
  public void testCanceledFutureThrowsCancellation() throws Exception {

    assertFalse(future.isDone());
    assertFalse(future.isCancelled());

    final CountDownLatch successLatch = new CountDownLatch(1);

    // Run cancellation in a separate thread as an extra thread-safety test.
    new Thread(new Runnable() {
      @Override
      public void run() {
        try {
          future.get();
        } catch (CancellationException expected) {
          successLatch.countDown();
        } catch (Exception ignored) {
          // All other errors are ignored, we expect a cancellation.
        }
      }
    }).start();

    assertFalse(future.isDone());
    assertFalse(future.isCancelled());

    future.cancel(true);

    assertTrue(future.isDone());
    assertTrue(future.isCancelled());

    assertTrue(successLatch.await(200, TimeUnit.MILLISECONDS));

    latch.countDown();
  }

  public void testListenersNotifiedOnError() throws Exception {
    final CountDownLatch successLatch = new CountDownLatch(1);
    final CountDownLatch listenerLatch = new CountDownLatch(1);

    ExecutorService exec = Executors.newCachedThreadPool();

    future.addListener(new Runnable() {
      @Override
      public void run() {
        listenerLatch.countDown();
      }
    }, exec);

    new Thread(new Runnable() {
      @Override
      public void run() {
        try {
          future.get();
        } catch (CancellationException expected) {
          successLatch.countDown();
        } catch (Exception ignored) {
          // No success latch count down.
        }
      }
    }).start();

    future.cancel(true);

    assertTrue(future.isCancelled());
    assertTrue(future.isDone());

    assertTrue(successLatch.await(200, TimeUnit.MILLISECONDS));
    assertTrue(listenerLatch.await(200, TimeUnit.MILLISECONDS));

    latch.countDown();

    exec.shutdown();
    exec.awaitTermination(100, TimeUnit.MILLISECONDS);
  }

  /**
   * Tests that all listeners complete, even if they were added before or after
   * the future was finishing.  Also acts as a concurrency test to make sure the
   * locking is done correctly when a future is finishing so that no listeners
   * can be lost.
   */
  public void testAllListenersCompleteSuccessfully()
      throws InterruptedException, ExecutionException {

    ExecutorService exec = Executors.newCachedThreadPool();

    int listenerCount = 20;
    final CountDownLatch listenerLatch = new CountDownLatch(listenerCount);

    // Test that listeners added both before and after the value is available
    // get called correctly.
    for (int i = 0; i < 20; i++) {

      // Right in the middle start up a thread to close the latch.
      if (i == 10) {
        new Thread(new Runnable() {
          @Override
          public void run() {
            latch.countDown();
          }
        }).start();
      }

      future.addListener(new Runnable() {
        @Override
        public void run() {
          listenerLatch.countDown();
        }
      }, exec);
    }

    assertSame(Boolean.TRUE, future.get());
    // Wait for the listener latch to complete.
    listenerLatch.await(500, TimeUnit.MILLISECONDS);

    exec.shutdown();
    exec.awaitTermination(500, TimeUnit.MILLISECONDS);
  }
}