/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project 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 io.netty.util.concurrent;

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

/**
 * The result of an asynchronous operation.
 */
@SuppressWarnings("ClassNameSameAsAncestorName")
public interface Future<V> extends java.util.concurrent.Future<V> {

    /**
     * Returns {@code true} if and only if the I/O operation was completed
     * successfully.
     */
    boolean isSuccess();

    /**
     * returns {@code true} if and only if the operation can be cancelled via {@link #cancel(boolean)}.
     */
    boolean isCancellable();

    /**
     * Returns the cause of the failed I/O operation if the I/O operation has
     * failed.
     *
     * @return the cause of the failure.
     *         {@code null} if succeeded or this future is not
     *         completed yet.
     */
    Throwable cause();

    /**
     * Adds the specified listener to this future.  The
     * specified listener is notified when this future is
     * {@linkplain #isDone() done}.  If this future is already
     * completed, the specified listener is notified immediately.
     */
    Future<V> addListener(GenericFutureListener<? extends Future<? super V>> listener);

    /**
     * Adds the specified listeners to this future.  The
     * specified listeners are notified when this future is
     * {@linkplain #isDone() done}.  If this future is already
     * completed, the specified listeners are notified immediately.
     */
    Future<V> addListeners(GenericFutureListener<? extends Future<? super V>>... listeners);

    /**
     * Removes the first occurrence of the specified listener from this future.
     * The specified listener is no longer notified when this
     * future is {@linkplain #isDone() done}.  If the specified
     * listener is not associated with this future, this method
     * does nothing and returns silently.
     */
    Future<V> removeListener(GenericFutureListener<? extends Future<? super V>> listener);

    /**
     * Removes the first occurrence for each of the listeners from this future.
     * The specified listeners are no longer notified when this
     * future is {@linkplain #isDone() done}.  If the specified
     * listeners are not associated with this future, this method
     * does nothing and returns silently.
     */
    Future<V> removeListeners(GenericFutureListener<? extends Future<? super V>>... listeners);

    /**
     * Waits for this future until it is done, and rethrows the cause of the failure if this future
     * failed.
     *
     * @throws CancellationException if the computation was cancelled
     * @throws {@link java.util.concurrent.CompletionException} if the computation threw an exception.
     * @throws InterruptedException if the current thread was interrupted while waiting
     *
     */
    Future<V> sync() throws InterruptedException;

    /**
     * Waits for this future until it is done, and rethrows the cause of the failure if this future
     * failed.
     *
     * @throws CancellationException if the computation was cancelled
     * @throws {@link java.util.concurrent.CompletionException} if the computation threw an exception.
     */
    Future<V> syncUninterruptibly();

    /**
     * Waits for this future to be completed.
     *
     * @throws InterruptedException
     *         if the current thread was interrupted
     */
    Future<V> await() throws InterruptedException;

    /**
     * Waits for this future to be completed without
     * interruption.  This method catches an {@link InterruptedException} and
     * discards it silently.
     */
    Future<V> awaitUninterruptibly();

    /**
     * Waits for this future to be completed within the
     * specified time limit.
     *
     * @return {@code true} if and only if the future was completed within
     *         the specified time limit
     *
     * @throws InterruptedException
     *         if the current thread was interrupted
     */
    boolean await(long timeout, TimeUnit unit) throws InterruptedException;

    /**
     * Waits for this future to be completed within the
     * specified time limit.
     *
     * @return {@code true} if and only if the future was completed within
     *         the specified time limit
     *
     * @throws InterruptedException
     *         if the current thread was interrupted
     */
    boolean await(long timeoutMillis) throws InterruptedException;

    /**
     * Waits for this future to be completed within the
     * specified time limit without interruption.  This method catches an
     * {@link InterruptedException} and discards it silently.
     *
     * @return {@code true} if and only if the future was completed within
     *         the specified time limit
     */
    boolean awaitUninterruptibly(long timeout, TimeUnit unit);

    /**
     * Waits for this future to be completed within the
     * specified time limit without interruption.  This method catches an
     * {@link InterruptedException} and discards it silently.
     *
     * @return {@code true} if and only if the future was completed within
     *         the specified time limit
     */
    boolean awaitUninterruptibly(long timeoutMillis);

    /**
     * Return the result without blocking. If the future is not done yet this will return {@code null}.
     *
     * As it is possible that a {@code null} value is used to mark the future as successful you also need to check
     * if the future is really done with {@link #isDone()} and not rely on the returned {@code null} value.
     */
    V getNow();

    /**
     * {@inheritDoc}
     *
     * If the cancellation was successful it will fail the future with a {@link CancellationException}.
     */
    @Override
    boolean cancel(boolean mayInterruptIfRunning);

    /**
     * Returns the {@link EventExecutor} that is tied to this {@link Future}.
     */
    EventExecutor executor();

    @Override
    default V get() throws InterruptedException, ExecutionException {
        await();

        Throwable cause = cause();
        if (cause == null) {
            return getNow();
        }
        if (cause instanceof CancellationException) {
            throw (CancellationException) cause;
        }
        throw new ExecutionException(cause);
    }

    @Override
    default V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        if (await(timeout, unit)) {
            Throwable cause = cause();
            if (cause == null) {
                return getNow();
            }
            if (cause instanceof CancellationException) {
                throw (CancellationException) cause;
            }
            throw new ExecutionException(cause);
        }
        throw new TimeoutException();
    }

    /**
     * Returns a {@link FutureCompletionStage} that reflects the state of this {@link Future} and so will receive
     * all updates as well.
     */
    default FutureCompletionStage<V> asStage() {
        return new DefaultFutureCompletionStage<>(this);
    }
}
