/*
 * Copyright (c) 2014 Brocade Communications Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.controller.cluster.datastore;

import com.google.common.base.Preconditions;
import com.google.common.collect.Iterables;
import com.google.common.util.concurrent.AbstractFuture;
import com.google.common.util.concurrent.AbstractListeningExecutorService;
import com.google.common.util.concurrent.CheckedFuture;
import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import org.opendaylight.controller.md.sal.common.api.data.LogicalDatastoreType;
import org.opendaylight.controller.md.sal.common.api.data.TransactionCommitFailedException;
import org.opendaylight.controller.md.sal.dom.api.DOMDataWriteTransaction;
import org.opendaylight.controller.md.sal.dom.broker.impl.AbstractDOMDataBroker;
import org.opendaylight.controller.md.sal.dom.broker.impl.TransactionCommitFailedExceptionMapper;
import org.opendaylight.controller.sal.core.spi.data.DOMStore;
import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
import org.opendaylight.yangtools.util.DurationStatisticsTracker;
import org.opendaylight.yangtools.util.concurrent.MappingCheckedFuture;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Implementation of DOMDataCommitExecutor that coordinates transaction commits concurrently. The 3
 * commit phases (canCommit, preCommit, and commit) are performed serially and non-blocking
 * (ie async) per transaction but multiple transaction commits can run concurrent.
 *
 * @author Thomas Pantelis
 */
public class ConcurrentDOMDataBroker extends AbstractDOMDataBroker {
    private static final Logger LOG = LoggerFactory.getLogger(ConcurrentDOMDataBroker.class);
    private static final String CAN_COMMIT = "CAN_COMMIT";
    private static final String PRE_COMMIT = "PRE_COMMIT";
    private static final String COMMIT = "COMMIT";

    private final DurationStatisticsTracker commitStatsTracker = DurationStatisticsTracker.createConcurrent();

    /**
     * This executor is used to execute Future listener callback Runnables async.
     */
    private final ExecutorService clientFutureCallbackExecutor;

    /**
     * This executor is re-used internally in calls to Futures#addCallback to avoid the overhead
     * of Futures#addCallback creating a MoreExecutors#sameThreadExecutor for each call.
     */
    private final ExecutorService internalFutureCallbackExecutor = new SimpleSameThreadExecutor();

    public ConcurrentDOMDataBroker(final Map<LogicalDatastoreType, DOMStore> datastores, ExecutorService listenableFutureExecutor) {
        super(datastores);
        this.clientFutureCallbackExecutor = Preconditions.checkNotNull(listenableFutureExecutor);
    }

    public DurationStatisticsTracker getCommitStatsTracker() {
        return commitStatsTracker;
    }

    @Override
    public CheckedFuture<Void, TransactionCommitFailedException> submit(DOMDataWriteTransaction transaction,
            Iterable<DOMStoreThreePhaseCommitCohort> cohorts) {

        Preconditions.checkArgument(transaction != null, "Transaction must not be null.");
        Preconditions.checkArgument(cohorts != null, "Cohorts must not be null.");
        LOG.debug("Tx: {} is submitted for execution.", transaction.getIdentifier());

        final int cohortSize = Iterables.size(cohorts);
        final AsyncNotifyingSettableFuture clientSubmitFuture =
                new AsyncNotifyingSettableFuture(clientFutureCallbackExecutor);

        doCanCommit(clientSubmitFuture, transaction, cohorts, cohortSize);

        return MappingCheckedFuture.create(clientSubmitFuture,
                TransactionCommitFailedExceptionMapper.COMMIT_ERROR_MAPPER);
    }

    private void doCanCommit(final AsyncNotifyingSettableFuture clientSubmitFuture,
            final DOMDataWriteTransaction transaction,
            final Iterable<DOMStoreThreePhaseCommitCohort> cohorts, final int cohortSize) {

        final long startTime = System.nanoTime();

        // Not using Futures.allAsList here to avoid its internal overhead.
        final AtomicInteger remaining = new AtomicInteger(cohortSize);
        FutureCallback<Boolean> futureCallback = new FutureCallback<Boolean>() {
            @Override
            public void onSuccess(Boolean result) {
                if (result == null || !result) {
                    handleException(clientSubmitFuture, transaction, cohorts, cohortSize,
                            CAN_COMMIT, TransactionCommitFailedExceptionMapper.CAN_COMMIT_ERROR_MAPPER,
                            new TransactionCommitFailedException(
                                            "Can Commit failed, no detailed cause available."));
                } else {
                    if(remaining.decrementAndGet() == 0) {
                        // All cohorts completed successfully - we can move on to the preCommit phase
                        doPreCommit(startTime, clientSubmitFuture, transaction, cohorts, cohortSize);
                    }
                }
            }

            @Override
            public void onFailure(Throwable t) {
                handleException(clientSubmitFuture, transaction, cohorts, cohortSize, CAN_COMMIT,
                        TransactionCommitFailedExceptionMapper.CAN_COMMIT_ERROR_MAPPER, t);
            }
        };

        for(DOMStoreThreePhaseCommitCohort cohort: cohorts) {
            ListenableFuture<Boolean> canCommitFuture = cohort.canCommit();
            Futures.addCallback(canCommitFuture, futureCallback, internalFutureCallbackExecutor);
        }
    }

    private void doPreCommit(final long startTime, final AsyncNotifyingSettableFuture clientSubmitFuture,
            final DOMDataWriteTransaction transaction,
            final Iterable<DOMStoreThreePhaseCommitCohort> cohorts, final int cohortSize) {

        // Not using Futures.allAsList here to avoid its internal overhead.
        final AtomicInteger remaining = new AtomicInteger(cohortSize);
        FutureCallback<Void> futureCallback = new FutureCallback<Void>() {
            @Override
            public void onSuccess(Void notUsed) {
                if(remaining.decrementAndGet() == 0) {
                    // All cohorts completed successfully - we can move on to the commit phase
                    doCommit(startTime, clientSubmitFuture, transaction, cohorts, cohortSize);
                }
            }

            @Override
            public void onFailure(Throwable t) {
                handleException(clientSubmitFuture, transaction, cohorts, cohortSize, PRE_COMMIT,
                        TransactionCommitFailedExceptionMapper.PRE_COMMIT_MAPPER, t);
            }
        };

        for(DOMStoreThreePhaseCommitCohort cohort: cohorts) {
            ListenableFuture<Void> preCommitFuture = cohort.preCommit();
            Futures.addCallback(preCommitFuture, futureCallback, internalFutureCallbackExecutor);
        }
    }

    private void doCommit(final long startTime, final AsyncNotifyingSettableFuture clientSubmitFuture,
            final DOMDataWriteTransaction transaction,
            final Iterable<DOMStoreThreePhaseCommitCohort> cohorts, final int cohortSize) {

        // Not using Futures.allAsList here to avoid its internal overhead.
        final AtomicInteger remaining = new AtomicInteger(cohortSize);
        FutureCallback<Void> futureCallback = new FutureCallback<Void>() {
            @Override
            public void onSuccess(Void notUsed) {
                if(remaining.decrementAndGet() == 0) {
                    // All cohorts completed successfully - we're done.
                    commitStatsTracker.addDuration(System.nanoTime() - startTime);

                    clientSubmitFuture.set();
                }
            }

            @Override
            public void onFailure(Throwable t) {
                handleException(clientSubmitFuture, transaction, cohorts, cohortSize, COMMIT,
                        TransactionCommitFailedExceptionMapper.COMMIT_ERROR_MAPPER, t);
            }
        };

        for(DOMStoreThreePhaseCommitCohort cohort: cohorts) {
            ListenableFuture<Void> commitFuture = cohort.commit();
            Futures.addCallback(commitFuture, futureCallback, internalFutureCallbackExecutor);
        }
    }

    private void handleException(final AsyncNotifyingSettableFuture clientSubmitFuture,
            final DOMDataWriteTransaction transaction,
            final Iterable<DOMStoreThreePhaseCommitCohort> cohorts, int cohortSize,
            final String phase, final TransactionCommitFailedExceptionMapper exMapper,
            final Throwable t) {

        if(clientSubmitFuture.isDone()) {
            // We must have had failures from multiple cohorts.
            return;
        }

        LOG.warn("Tx: {} Error during phase {}, starting Abort", transaction.getIdentifier(), phase, t);
        Exception e;
        if(t instanceof Exception) {
            e = (Exception)t;
        } else {
            e = new RuntimeException("Unexpected error occurred", t);
        }

        final TransactionCommitFailedException clientException = exMapper.apply(e);

        // Transaction failed - tell all cohorts to abort.

        @SuppressWarnings("unchecked")
        ListenableFuture<Void>[] canCommitFutures = new ListenableFuture[cohortSize];
        int i = 0;
        for(DOMStoreThreePhaseCommitCohort cohort: cohorts) {
            canCommitFutures[i++] = cohort.abort();
        }

        ListenableFuture<List<Void>> combinedFuture = Futures.allAsList(canCommitFutures);
        Futures.addCallback(combinedFuture, new FutureCallback<List<Void>>() {
            @Override
            public void onSuccess(List<Void> notUsed) {
                // Propagate the original exception to the client.
                clientSubmitFuture.setException(clientException);
            }

            @Override
            public void onFailure(Throwable t) {
                LOG.error("Tx: {} Error during Abort.", transaction.getIdentifier(), t);

                // Propagate the original exception as that is what caused the Tx to fail and is
                // what's interesting to the client.
                clientSubmitFuture.setException(clientException);
            }
        }, internalFutureCallbackExecutor);
    }

    /**
     * A settable future that uses an {@link Executor} to execute listener callback Runnables,
     * registered via {@link #addListener}, asynchronously when this future completes. This is
     * done to guarantee listener executions are off-loaded onto another thread to avoid blocking
     * the thread that completed this future, as a common use case is to pass an executor that runs
     * tasks in the same thread as the caller (ie MoreExecutors#sameThreadExecutor)
     * to {@link #addListener}.
     *
     * FIXME: This class should probably be moved to yangtools common utils for re-usability and
     * unified with AsyncNotifyingListenableFutureTask.
     */
    private static class AsyncNotifyingSettableFuture extends AbstractFuture<Void> {

        /**
         * ThreadLocal used to detect if the task completion thread is running the future listener Runnables.
         */
        private static final ThreadLocal<Boolean> ON_TASK_COMPLETION_THREAD_TL = new ThreadLocal<Boolean>();

        private final ExecutorService listenerExecutor;

        AsyncNotifyingSettableFuture(ExecutorService listenerExecutor) {
            this.listenerExecutor = listenerExecutor;
        }

        @Override
        public void addListener(final Runnable listener, final Executor executor) {
            // Wrap the listener Runnable in a DelegatingRunnable. If the specified executor is one
            // that runs tasks in the same thread as the caller submitting the task
            // (e.g. {@link com.google.common.util.concurrent.MoreExecutors#sameThreadExecutor}) and
            // the listener is executed from the #set methods, then the DelegatingRunnable will detect
            // this via the ThreadLocal and submit the listener Runnable to the listenerExecutor.
            //
            // On the other hand, if this task is already complete, the call to ExecutionList#add in
            // superclass will execute the listener Runnable immediately and, since the ThreadLocal
            // won't be set, the DelegatingRunnable will run the listener Runnable inline.
            super.addListener(new DelegatingRunnable(listener, listenerExecutor), executor);
        }

        boolean set() {
            ON_TASK_COMPLETION_THREAD_TL.set(Boolean.TRUE);
            try {
                return super.set(null);
            } finally {
                ON_TASK_COMPLETION_THREAD_TL.set(null);
            }
        }

        @Override
        protected boolean setException(Throwable throwable) {
            ON_TASK_COMPLETION_THREAD_TL.set(Boolean.TRUE);
            try {
                return super.setException(throwable);
            } finally {
                ON_TASK_COMPLETION_THREAD_TL.set(null);
            }
        }

        private static final class DelegatingRunnable implements Runnable {
            private final Runnable delegate;
            private final Executor executor;

            DelegatingRunnable(final Runnable delegate, final Executor executor) {
                this.delegate = Preconditions.checkNotNull(delegate);
                this.executor = Preconditions.checkNotNull(executor);
            }

            @Override
            public void run() {
                if (ON_TASK_COMPLETION_THREAD_TL.get() != null) {
                    // We're running on the task completion thread so off-load to the executor.
                    LOG.trace("Submitting ListenenableFuture Runnable from thread {} to executor {}",
                            Thread.currentThread().getName(), executor);
                    executor.execute(delegate);
                } else {
                    // We're not running on the task completion thread so run the delegate inline.
                    LOG.trace("Executing ListenenableFuture Runnable on this thread: {}",
                            Thread.currentThread().getName());
                    delegate.run();
                }
            }
        }
    }

    /**
     * A simple same-thread executor without the internal locking overhead that
     * MoreExecutors#sameThreadExecutor has. The #execute method is the only one of concern - we
     * don't shutdown the executor so the other methods irrelevant.
     */
    private static class SimpleSameThreadExecutor extends AbstractListeningExecutorService {

        @Override
        public void execute(Runnable command) {
            command.run();
        }

        @Override
        public boolean awaitTermination(long arg0, TimeUnit arg1) throws InterruptedException {
            return true;
        }

        @Override
        public boolean isShutdown() {
            return false;
        }

        @Override
        public boolean isTerminated() {
            return false;
        }

        @Override
        public void shutdown() {
        }

        @Override
        public List<Runnable> shutdownNow() {
            return null;
        }
    }
}