java/dagger/producers/internal/Producers.java

/*
 * Copyright (C) 2014 The Dagger 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 dagger.producers.internal;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.util.concurrent.Futures.catchingAsync;
import static com.google.common.util.concurrent.Futures.transform;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;

import com.google.common.base.Function;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.util.concurrent.AsyncFunction;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import dagger.producers.Produced;
import dagger.producers.Producer;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.inject.Provider;

/**
 * Utility methods for use in generated producer code.
 */
public final class Producers {
  /**
   * Returns a future of {@link Produced} that represents the completion (either success or failure)
   * of the given future. If the input future succeeds, then the resulting future also succeeds with
   * a successful {@code Produced}; if the input future fails, then the resulting future succeeds
   * with a failing {@code Produced}.
   *
   * <p>Cancelling the resulting future will propagate the cancellation to the input future; but
   * cancelling the input future will trigger the resulting future to succeed with a failing
   * {@code Produced}.
   */
  // TODO(beder): Document what happens with an InterruptedException after you figure out how to
  // trigger one in a test.
  public static <T> ListenableFuture<Produced<T>> createFutureProduced(ListenableFuture<T> future) {
    return catchingAsync(
        transform(future, Producers.<T>resultToProduced(), directExecutor()),
        Throwable.class,
        Producers.<T>futureFallbackForProduced(),
        directExecutor());
  }

  private static final Function<Object, Produced<Object>> RESULT_TO_PRODUCED =
      new Function<Object, Produced<Object>>() {
        @Override
        public Produced<Object> apply(Object result) {
          return Produced.successful(result);
        }
      };

  @SuppressWarnings({"unchecked", "rawtypes"}) // bivariant implementation
  private static <T> Function<T, Produced<T>> resultToProduced() {
    return (Function) RESULT_TO_PRODUCED;
  }

  private static final AsyncFunction<Throwable, Produced<Object>> FUTURE_FALLBACK_FOR_PRODUCED =
      new AsyncFunction<Throwable, Produced<Object>>() {
        @Override
        public ListenableFuture<Produced<Object>> apply(Throwable t) throws Exception {
          Produced<Object> produced = Produced.failed(t);
          return Futures.immediateFuture(produced);
        }
      };

  @SuppressWarnings({"unchecked", "rawtypes"}) // bivariant implementation
  private static <T> AsyncFunction<Throwable, Produced<T>> futureFallbackForProduced() {
    return (AsyncFunction) FUTURE_FALLBACK_FOR_PRODUCED;
  }

  /**
   * Returns a future of a {@code Set} that contains a single element: the result of the input
   * future.
   */
  public static <T> ListenableFuture<Set<T>> createFutureSingletonSet(ListenableFuture<T> future) {
    return transform(
        future,
        new Function<T, Set<T>>() {
          @Override
          public Set<T> apply(T value) {
            return ImmutableSet.of(value);
          }
        },
        directExecutor());
  }

  /**
   * Creates a new {@code ListenableFuture} whose value is a set containing the values of all its
   * input futures, if all succeed. If any input fails, the returned future fails immediately.
   *
   * <p>This is the set equivalent of {@link Futures#allAsList}.
   */
  public static <T> ListenableFuture<Set<T>> allAsSet(
      Iterable<? extends ListenableFuture<? extends T>> futures) {
    return transform(
        Futures.allAsList(futures),
        new Function<List<T>, Set<T>>() {
          @Override
          public Set<T> apply(List<T> values) {
            return ImmutableSet.copyOf(values);
          }
        },
        directExecutor());
  }

  /**
   * Returns a producer that immediately executes the binding logic for the given provider every
   * time it is called.
   */
  public static <T> Producer<T> producerFromProvider(final Provider<T> provider) {
    checkNotNull(provider);
    return new CompletedProducer<T>() {
      @Override
      public ListenableFuture<T> get() {
        return Futures.immediateFuture(provider.get());
      }
    };
  }

  /**
   * Returns a producer that succeeds with the given value.
   *
   * @deprecated Prefer the non-internal version of this method: {@link
   * dagger.producers.Producers#immediateProducer(Object)}.
   */
  @Deprecated
  public static <T> Producer<T> immediateProducer(T value) {
    return dagger.producers.Producers.immediateProducer(value);
  }

  /**
   * Returns a producer that fails with the given exception.
   *
   * @deprecated Prefer the non-internal version of this method: {@link
   * dagger.producers.Producers#immediateFailedProducer(Throwable)}.
   */
  @Deprecated
  public static <T> Producer<T> immediateFailedProducer(Throwable throwable) {
    return dagger.producers.Producers.immediateFailedProducer(throwable);
  }

  /**
   * Returns a new view of the given {@code producer} if and only if it is a {@link
   * CancellableProducer}. Cancelling the returned producer's future will not cancel the underlying
   * task for the given producer.
   *
   * @throws IllegalArgumentException if {@code producer} is not a {@code CancellableProducer}
   */
  public static <T> Producer<T> nonCancellationPropagatingViewOf(Producer<T> producer) {
    // This is a hack until we change the types of Producer fields to be CancellableProducer or
    // some other type.
    if (producer instanceof CancellableProducer) {
      return ((CancellableProducer<T>) producer).newDependencyView();
    }
    throw new IllegalArgumentException(
        "nonCancellationPropagatingViewOf called with non-CancellableProducer: " + producer);
  }

  /**
   * Returns a new view of the given {@code producer} for use as an entry point in a production
   * component, if and only if it is a {@link CancellableProducer}. When the returned producer's
   * future is cancelled, the given {@code cancellable} will also be cancelled.
   *
   * @throws IllegalArgumentException if {@code producer} is not a {@code CancellableProducer}
   */
  public static <T> Producer<T> entryPointViewOf(
      Producer<T> producer, CancellationListener cancellationListener) {
    // This is a hack until we change the types of Producer fields to be CancellableProducer or
    // some other type.
    if (producer instanceof CancellableProducer) {
      return ((CancellableProducer<T>) producer).newEntryPointView(cancellationListener);
    }
    throw new IllegalArgumentException(
        "entryPointViewOf called with non-CancellableProducer: " + producer);
  }

  /**
   * Calls {@code cancel} on the given {@code producer} if it is a {@link CancellableProducer}.
   *
   * @throws IllegalArgumentException if {@code producer} is not a {@code CancellableProducer}
   */
  public static void cancel(Producer<?> producer, boolean mayInterruptIfRunning) {
    // This is a hack until we change the types of Producer fields to be CancellableProducer or
    // some other type.
    if (producer instanceof CancellableProducer) {
      ((CancellableProducer<?>) producer).cancel(mayInterruptIfRunning);
    } else {
      throw new IllegalArgumentException("cancel called with non-CancellableProducer: " + producer);
    }
  }

  private static final Producer<Map<Object, Object>> EMPTY_MAP_PRODUCER =
      dagger.producers.Producers.<Map<Object, Object>>immediateProducer(ImmutableMap.of());

  @SuppressWarnings("unchecked") // safe contravariant cast
  public static <K, V> Producer<Map<K, V>> emptyMapProducer() {
    return (Producer<Map<K, V>>) (Producer) EMPTY_MAP_PRODUCER;
  }

  /**
   * A {@link CancellableProducer} which can't be cancelled because it represents an
   * already-completed task.
   */
  private abstract static class CompletedProducer<T> implements CancellableProducer<T> {
    @Override
    public void cancel(boolean mayInterruptIfRunning) {}

    @Override
    public Producer<T> newDependencyView() {
      return this;
    }

    @Override
    public Producer<T> newEntryPointView(CancellationListener cancellationListener) {
      return this;
    }
  }

  private Producers() {}
}