/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.action.support;

import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.action.ActionFuture;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.cluster.service.ClusterApplierService;
import org.elasticsearch.cluster.service.MasterService;
import org.elasticsearch.common.util.concurrent.EsExecutors;
import org.elasticsearch.common.util.concurrent.FutureUtils;
import org.elasticsearch.common.util.concurrent.UncategorizedExecutionException;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.Transports;

import java.util.Objects;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;

public class PlainActionFuture<T> implements ActionFuture<T>, ActionListener<T> {

    @Override
    public void onResponse(@Nullable T result) {
        set(result);
    }

    @Override
    public void onFailure(Exception e) {
        assert assertCompleteAllowed();
        if (sync.setException(Objects.requireNonNull(e))) {
            done(false);
        }
    }

    private static final String BLOCKING_OP_REASON = "Blocking operation";

    /**
     * Synchronization control.
     */
    private final Sync<T> sync = new Sync<>();

    /*
     * Improve the documentation of when InterruptedException is thrown. Our
     * behavior matches the JDK's, but the JDK's documentation is misleading.
     */

    /**
     * {@inheritDoc}
     * <p>
     * The default {@link PlainActionFuture} implementation throws {@code
     * InterruptedException} if the current thread is interrupted before or during
     * the call, even if the value is already available.
     *
     * @throws InterruptedException  if the current thread was interrupted before
     *                               or during the call (optional but recommended).
     * @throws CancellationException {@inheritDoc}
     */
    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException, ExecutionException {
        assert timeout <= 0 || blockingAllowed();
        return sync.get(unit.toNanos(timeout));
    }

    /*
     * Improve the documentation of when InterruptedException is thrown. Our
     * behavior matches the JDK's, but the JDK's documentation is misleading.
     */

    /**
     * {@inheritDoc}
     * <p>
     * The default {@link PlainActionFuture<Object>} implementation throws {@code
     * InterruptedException} if the current thread is interrupted before or during
     * the call, even if the value is already available.
     *
     * @throws InterruptedException  if the current thread was interrupted before
     *                               or during the call (optional but recommended).
     * @throws CancellationException {@inheritDoc}
     */
    @Override
    public T get() throws InterruptedException, ExecutionException {
        assert blockingAllowed();
        return sync.get();
    }

    // protected so that it can be overridden in specific instances
    protected boolean blockingAllowed() {
        return Transports.assertNotTransportThread(BLOCKING_OP_REASON)
            && ThreadPool.assertNotScheduleThread(BLOCKING_OP_REASON)
            && ClusterApplierService.assertNotClusterStateUpdateThread(BLOCKING_OP_REASON)
            && MasterService.assertNotMasterUpdateThread(BLOCKING_OP_REASON);
    }

    @Override
    public boolean isDone() {
        return sync.isDone();
    }

    @Override
    public boolean isCancelled() {
        return sync.isCancelled();
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        assert assertCompleteAllowed();
        if (sync.cancel() == false) {
            return false;
        }
        done(false);
        return true;
    }

    /**
     * Subclasses should invoke this method to set the result of the computation
     * to {@code value}.  This will set the state of the future to
     * {@link PlainActionFuture.Sync#COMPLETED} and call {@link #done(boolean)} if the
     * state was successfully changed.
     *
     * @param value the value that was the result of the task.
     * @return true if the state was successfully changed.
     */
    protected final boolean set(@Nullable T value) {
        assert assertCompleteAllowed();
        boolean result = sync.set(value);
        if (result) {
            done(true);
        }
        return result;
    }

    /**
     * Called when the {@link PlainActionFuture<Object>} is completed. The {@code success} boolean indicates if the {@link
     * PlainActionFuture<Object>} was successfully completed (the value is {@code true}). In the cases the {@link PlainActionFuture<Object>}
     * was completed with an error or cancelled the value is {@code false}.
     *
     * @param success indicates if the {@link PlainActionFuture<Object>} was completed with success (true); in other cases it equals false
     */
    protected void done(boolean success) {}

    @Override
    public T actionGet() {
        try {
            return FutureUtils.get(this);
        } catch (ElasticsearchException e) {
            throw unwrapEsException(e);
        }
    }

    @Override
    public T actionGet(TimeValue timeout) {
        return actionGet(timeout.millis(), TimeUnit.MILLISECONDS);
    }

    @Override
    public T actionGet(long timeout, TimeUnit unit) {
        try {
            return FutureUtils.get(this, timeout, unit);
        } catch (ElasticsearchException e) {
            throw unwrapEsException(e);
        }
    }

    /**
     * Return the result of this future, similarly to {@link FutureUtils#get} with a zero timeout except that this method ignores the
     * interrupted status of the calling thread.
     * <p>
     * If the future completed exceptionally then this method throws an {@link ExecutionException} whose cause is the completing exception.
     * <p>
     * It is not valid to call this method if the future is incomplete.
     *
     * @return the result of this future, if it has been completed successfully.
     * @throws ExecutionException if this future was completed exceptionally.
     * @throws CancellationException if this future was cancelled.
     * @throws IllegalStateException if this future is incomplete.
     */
    public T result() throws ExecutionException {
        return sync.result();
    }

    /**
     * <p>Following the contract of {@link AbstractQueuedSynchronizer} we create a
     * private subclass to hold the synchronizer.  This synchronizer is used to
     * implement the blocking and waiting calls as well as to handle state changes
     * in a thread-safe manner.  The current state of the future is held in the
     * Sync state, and the lock is released whenever the state changes to either
     * {@link #COMPLETED} or {@link #CANCELLED}.
     * <p>
     * To avoid races between threads doing release and acquire, we transition
     * to the final state in two steps.  One thread will successfully CAS from
     * RUNNING to COMPLETING, that thread will then set the result of the
     * computation, and only then transition to COMPLETED or CANCELLED.
     * <p>
     * We don't use the integer argument passed between acquire methods, so we
     * pass around a -1 everywhere.
     */
    static final class Sync<V> extends AbstractQueuedSynchronizer {
        /* Valid states. */
        static final int RUNNING = 0;
        static final int COMPLETING = 1;
        static final int COMPLETED = 2;
        static final int CANCELLED = 4;

        private V value;
        private Exception exception;

        /*
         * Acquisition succeeds if the future is done, otherwise it fails.
         */
        @Override
        protected int tryAcquireShared(int ignored) {
            if (isDone()) {
                return 1;
            }
            return -1;
        }

        /*
         * We always allow a release to go through, this means the state has been
         * successfully changed and the result is available.
         */
        @Override
        protected boolean tryReleaseShared(int finalState) {
            setState(finalState);
            return true;
        }

        /**
         * Blocks until the task is complete or the timeout expires.  Throws a
         * {@link TimeoutException} if the timer expires, otherwise behaves like
         * {@link #get()}.
         */
        V get(long nanos) throws TimeoutException, CancellationException, ExecutionException, InterruptedException {

            // Attempt to acquire the shared lock with a timeout.
            if (tryAcquireSharedNanos(-1, nanos) == false) {
                throw new TimeoutException("Timeout waiting for task.");
            }

            return getValue();
        }

        /**
         * Blocks until {@link #complete(Object, Exception, int)} has been
         * successfully called.  Throws a {@link CancellationException} if the task
         * was cancelled, or a {@link ExecutionException} if the task completed with
         * an error.
         */
        V get() throws CancellationException, ExecutionException, InterruptedException {

            // Acquire the shared lock allowing interruption.
            acquireSharedInterruptibly(-1);
            return getValue();
        }

        /**
         * Implementation of the actual value retrieval.  Will return the value
         * on success, an exception on failure, a cancellation on cancellation, or
         * an illegal state if the synchronizer is in an invalid state.
         */
        private V getValue() throws CancellationException, ExecutionException {
            int state = getState();
            switch (state) {
                case COMPLETED:
                    if (exception != null) {
                        throw new ExecutionException(exception);
                    } else {
                        return value;
                    }

                case CANCELLED:
                    throw new CancellationException("Task was cancelled.");

                default:
                    throw new IllegalStateException("Error, synchronizer in invalid state: " + state);
            }
        }

        V result() throws CancellationException, ExecutionException {
            assert isDone() : "Error, synchronizer in invalid state: " + getState();
            return getValue();
        }

        /**
         * Checks if the state is {@link #COMPLETED} or {@link #CANCELLED}.
         */
        boolean isDone() {
            return (getState() & (COMPLETED | CANCELLED)) != 0;
        }

        /**
         * Checks if the state is {@link #CANCELLED}.
         */
        boolean isCancelled() {
            return getState() == CANCELLED;
        }

        /**
         * Transition to the COMPLETED state and set the value.
         */
        boolean set(@Nullable V v) {
            return complete(v, null, COMPLETED);
        }

        /**
         * Transition to the COMPLETED state and set the exception.
         */
        boolean setException(Exception e) {
            return complete(null, e, COMPLETED);
        }

        /**
         * Transition to the CANCELLED state.
         */
        boolean cancel() {
            return complete(null, null, CANCELLED);
        }

        /**
         * Implementation of completing a task.  Either {@code v} or {@code e} will
         * be set but not both.  The {@code finalState} is the state to change to
         * from {@link #RUNNING}.  If the state is not in the RUNNING state we
         * return {@code false} after waiting for the state to be set to a valid
         * final state ({@link #COMPLETED} or {@link #CANCELLED}).
         *
         * @param v          the value to set as the result of the computation.
         * @param e          the exception to set as the result of the computation.
         * @param finalState the state to transition to.
         */
        private boolean complete(@Nullable V v, @Nullable Exception e, int finalState) {
            boolean doCompletion = compareAndSetState(RUNNING, COMPLETING);
            if (doCompletion) {
                // If this thread successfully transitioned to COMPLETING, set the value
                // and exception and then release to the final state.
                this.value = v;
                this.exception = e;
                releaseShared(finalState);
            } else if (getState() == COMPLETING) {
                // If some other thread is currently completing the future, block until
                // they are done so we can guarantee completion.
                // Don't use acquire here, to prevent false-positive deadlock detection
                // when multiple threads from the same pool are completing the future
                while (isDone() == false) {
                    Thread.onSpinWait();
                }
            }
            return doCompletion;
        }
    }

    private static RuntimeException unwrapEsException(ElasticsearchException esEx) {
        Throwable root = esEx.unwrapCause();
        if (root instanceof RuntimeException runtimeException) {
            return runtimeException;
        }
        return new UncategorizedExecutionException("Failed execution", root);
    }

    private boolean assertCompleteAllowed() {
        Thread waiter = sync.getFirstQueuedThread();
        assert waiter == null || allowedExecutors(waiter, Thread.currentThread())
            : "cannot complete future on thread "
                + Thread.currentThread()
                + " with waiter on thread "
                + waiter
                + ", could deadlock if pool was full\n"
                + ExceptionsHelper.formatStackTrace(waiter.getStackTrace());
        return true;
    }

    // only used in assertions
    boolean allowedExecutors(Thread blockedThread, Thread completingThread) {
        // this should only be used to validate thread interactions, like not waiting for a future completed on the same
        // executor, hence calling it with the same thread indicates a bug in the assertion using this.
        assert blockedThread != completingThread : "only call this for different threads";
        String blockedThreadName = EsExecutors.executorName(blockedThread);
        String completingThreadName = EsExecutors.executorName(completingThread);
        return blockedThreadName == null || completingThreadName == null || blockedThreadName.equals(completingThreadName) == false;
    }
}