/*
 * Copyright (C) 2008 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;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A delegating wrapper around a {@link ListenableFuture} that adds support for the {@link
 * #checkedGet()} and {@link #checkedGet(long, TimeUnit)} methods.
 *
 * @author Sven Mawson
 * @since 1.0
 */
@Beta
@GwtIncompatible
public abstract class AbstractCheckedFuture<V, X extends Exception>
    extends ForwardingListenableFuture.SimpleForwardingListenableFuture<V>
    implements CheckedFuture<V, X> {
  /**
   * Constructs an {@code AbstractCheckedFuture} that wraps a delegate.
   */
  protected AbstractCheckedFuture(ListenableFuture<V> delegate) {
    super(delegate);
  }

  /**
   * Translates from an {@link InterruptedException}, {@link CancellationException} or {@link
   * ExecutionException} thrown by {@code get} to an exception of type {@code X} to be thrown by
   * {@code checkedGet}. Subclasses must implement this method.
   *
   * <p>If {@code e} is an {@code InterruptedException}, the calling {@code checkedGet} method has
   * already restored the interrupt after catching the exception. If an implementation of {@link
   * #mapException(Exception)} wishes to swallow the interrupt, it can do so by calling {@link
   * Thread#interrupted()}.
   *
   * <p>Subclasses may choose to throw, rather than return, a subclass of {@code RuntimeException}
   * to allow creating a CheckedFuture that throws both checked and unchecked exceptions.
   */
  // We might like @ForOverride here, but some subclasses invoke this from their get() methods.
  protected abstract X mapException(Exception e);

  /**
   * {@inheritDoc}
   *
   * <p>This implementation calls {@link #get()} and maps that method's standard exceptions to
   * instances of type {@code X} using {@link #mapException}.
   *
   * <p>In addition, if {@code get} throws an {@link InterruptedException}, this implementation will
   * set the current thread's interrupt status before calling {@code mapException}.
   *
   * @throws X if {@link #get()} throws an {@link InterruptedException}, {@link
   *     CancellationException}, or {@link ExecutionException}
   */
  @CanIgnoreReturnValue
  @Override
  public V checkedGet() throws X {
    try {
      return get();
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      throw mapException(e);
    } catch (CancellationException e) {
      throw mapException(e);
    } catch (ExecutionException e) {
      throw mapException(e);
    }
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation calls {@link #get(long, TimeUnit)} and maps that method's standard
   * exceptions (excluding {@link TimeoutException}, which is propagated) to instances of type
   * {@code X} using {@link #mapException}.
   *
   * <p>In addition, if {@code get} throws an {@link InterruptedException}, this implementation will
   * set the current thread's interrupt status before calling {@code mapException}.
   *
   * @throws X if {@link #get()} throws an {@link InterruptedException}, {@link
   *     CancellationException}, or {@link ExecutionException}
   */
  @CanIgnoreReturnValue
  @Override
  public V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X {
    try {
      return get(timeout, unit);
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      throw mapException(e);
    } catch (CancellationException e) {
      throw mapException(e);
    } catch (ExecutionException e) {
      throw mapException(e);
    }
  }
}
