/*
 * 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 akka.actor.ActorRef;
import akka.actor.Status.Failure;
import akka.serialization.Serialization;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.common.primitives.UnsignedLong;
import com.google.common.util.concurrent.FutureCallback;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import javax.annotation.Nonnull;
import org.opendaylight.controller.cluster.access.concepts.TransactionIdentifier;
import org.opendaylight.controller.cluster.datastore.messages.AbortTransactionReply;
import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
import org.opendaylight.controller.cluster.datastore.messages.BatchedModificationsReply;
import org.opendaylight.controller.cluster.datastore.messages.CanCommitTransaction;
import org.opendaylight.controller.cluster.datastore.messages.CanCommitTransactionReply;
import org.opendaylight.controller.cluster.datastore.messages.CommitTransaction;
import org.opendaylight.controller.cluster.datastore.messages.CommitTransactionReply;
import org.opendaylight.controller.cluster.datastore.messages.ForwardedReadyTransaction;
import org.opendaylight.controller.cluster.datastore.messages.ReadyLocalTransaction;
import org.opendaylight.controller.cluster.datastore.messages.ReadyTransactionReply;
import org.opendaylight.controller.cluster.datastore.messages.VersionedExternalizableMessage;
import org.opendaylight.controller.cluster.datastore.utils.AbstractBatchedModificationsCursor;
import org.opendaylight.yangtools.concepts.Identifier;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidate;
import org.slf4j.Logger;

/**
 * Coordinates commits for a shard ensuring only one concurrent 3-phase commit.
 *
 * @author Thomas Pantelis
 */
final class ShardCommitCoordinator {

    // Interface hook for unit tests to replace or decorate the ShardDataTreeCohorts.
    @VisibleForTesting
    public interface CohortDecorator {
        ShardDataTreeCohort decorate(Identifier transactionID, ShardDataTreeCohort actual);
    }

    private final Map<Identifier, CohortEntry> cohortCache = new HashMap<>();

    private final ShardDataTree dataTree;

    private final Logger log;

    private final String name;

    // This is a hook for unit tests to replace or decorate the ShardDataTreeCohorts.
    @VisibleForTesting
    private CohortDecorator cohortDecorator;

    private ReadyTransactionReply readyTransactionReply;

    ShardCommitCoordinator(final ShardDataTree dataTree, final Logger log, final String name) {
        this.log = log;
        this.name = name;
        this.dataTree = Preconditions.checkNotNull(dataTree);
    }

    int getCohortCacheSize() {
        return cohortCache.size();
    }

    private String persistenceId() {
        return dataTree.logContext();
    }

    private ReadyTransactionReply readyTransactionReply(final ActorRef cohort) {
        if (readyTransactionReply == null) {
            readyTransactionReply = new ReadyTransactionReply(Serialization.serializedActorPath(cohort));
        }

        return readyTransactionReply;
    }

    /**
     * This method is called to ready a transaction that was prepared by ShardTransaction actor. It caches
     * the prepared cohort entry for the given transactions ID in preparation for the subsequent 3-phase commit.
     *
     * @param ready the ForwardedReadyTransaction message to process
     * @param sender the sender of the message
     * @param shard the transaction's shard actor
     * @param schema
     */
    void handleForwardedReadyTransaction(final ForwardedReadyTransaction ready, final ActorRef sender,
            final Shard shard) {
        log.debug("{}: Readying transaction {}, client version {}", name,
                ready.getTransactionID(), ready.getTxnClientVersion());

        final ShardDataTreeCohort cohort = ready.getTransaction().ready();
        final CohortEntry cohortEntry = CohortEntry.createReady(cohort, ready.getTxnClientVersion());
        cohortCache.put(cohortEntry.getTransactionID(), cohortEntry);

        if (ready.isDoImmediateCommit()) {
            cohortEntry.setDoImmediateCommit(true);
            cohortEntry.setReplySender(sender);
            cohortEntry.setShard(shard);
            handleCanCommit(cohortEntry);
        } else {
            // The caller does not want immediate commit - the 3-phase commit will be coordinated by the
            // front-end so send back a ReadyTransactionReply with our actor path.
            sender.tell(readyTransactionReply(shard.self()), shard.self());
        }
    }

    /**
     * This method handles a BatchedModifications message for a transaction being prepared directly on the
     * Shard actor instead of via a ShardTransaction actor. If there's no currently cached
     * DOMStoreWriteTransaction, one is created. The batched modifications are applied to the write Tx. If
     * the BatchedModifications is ready to commit then a DOMStoreThreePhaseCommitCohort is created.
     *
     * @param batched the BatchedModifications message to process
     * @param sender the sender of the message
     */
    void handleBatchedModifications(final BatchedModifications batched, final ActorRef sender, final Shard shard) {
        CohortEntry cohortEntry = cohortCache.get(batched.getTransactionID());
        if (cohortEntry == null) {
            cohortEntry = CohortEntry.createOpen(dataTree.newReadWriteTransaction(batched.getTransactionID()),
                batched.getVersion());
            cohortCache.put(cohortEntry.getTransactionID(), cohortEntry);
        }

        if (log.isDebugEnabled()) {
            log.debug("{}: Applying {} batched modifications for Tx {}", name,
                    batched.getModifications().size(), batched.getTransactionID());
        }

        cohortEntry.applyModifications(batched.getModifications());

        if (batched.isReady()) {
            if (cohortEntry.getLastBatchedModificationsException() != null) {
                cohortCache.remove(cohortEntry.getTransactionID());
                throw cohortEntry.getLastBatchedModificationsException();
            }

            if (cohortEntry.getTotalBatchedModificationsReceived() != batched.getTotalMessagesSent()) {
                cohortCache.remove(cohortEntry.getTransactionID());
                throw new IllegalStateException(String.format(
                        "The total number of batched messages received %d does not match the number sent %d",
                        cohortEntry.getTotalBatchedModificationsReceived(), batched.getTotalMessagesSent()));
            }

            if (log.isDebugEnabled()) {
                log.debug("{}: Readying Tx {}, client version {}", name,
                        batched.getTransactionID(), batched.getVersion());
            }

            cohortEntry.setDoImmediateCommit(batched.isDoCommitOnReady());
            cohortEntry.ready(cohortDecorator);

            if (batched.isDoCommitOnReady()) {
                cohortEntry.setReplySender(sender);
                cohortEntry.setShard(shard);
                handleCanCommit(cohortEntry);
            } else {
                sender.tell(readyTransactionReply(shard.self()), shard.self());
            }
        } else {
            sender.tell(new BatchedModificationsReply(batched.getModifications().size()), shard.self());
        }
    }

    /**
     * This method handles {@link ReadyLocalTransaction} message. All transaction modifications have
     * been prepared beforehand by the sender and we just need to drive them through into the
     * dataTree.
     *
     * @param message the ReadyLocalTransaction message to process
     * @param sender the sender of the message
     * @param shard the transaction's shard actor
     */
    void handleReadyLocalTransaction(final ReadyLocalTransaction message, final ActorRef sender, final Shard shard) {
        final ShardDataTreeCohort cohort = dataTree.createReadyCohort(message.getTransactionID(),
            message.getModification());
        final CohortEntry cohortEntry = CohortEntry.createReady(cohort, DataStoreVersions.CURRENT_VERSION);
        cohortCache.put(cohortEntry.getTransactionID(), cohortEntry);
        cohortEntry.setDoImmediateCommit(message.isDoCommitOnReady());

        log.debug("{}: Applying local modifications for Tx {}", name, message.getTransactionID());

        if (message.isDoCommitOnReady()) {
            cohortEntry.setReplySender(sender);
            cohortEntry.setShard(shard);
            handleCanCommit(cohortEntry);
        } else {
            sender.tell(readyTransactionReply(shard.self()), shard.self());
        }
    }

    Collection<BatchedModifications> createForwardedBatchedModifications(final BatchedModifications from,
            final int maxModificationsPerBatch) {
        CohortEntry cohortEntry = cohortCache.remove(from.getTransactionID());
        if (cohortEntry == null || cohortEntry.getTransaction() == null) {
            return Collections.singletonList(from);
        }

        cohortEntry.applyModifications(from.getModifications());

        final LinkedList<BatchedModifications> newModifications = new LinkedList<>();
        cohortEntry.getTransaction().getSnapshot().applyToCursor(new AbstractBatchedModificationsCursor() {
            @Override
            protected BatchedModifications getModifications() {
                if (newModifications.isEmpty() ||
                        newModifications.getLast().getModifications().size() >= maxModificationsPerBatch) {
                    newModifications.add(new BatchedModifications(from.getTransactionID(), from.getVersion()));
                }

                return newModifications.getLast();
            }
        });

        BatchedModifications last = newModifications.getLast();
        last.setDoCommitOnReady(from.isDoCommitOnReady());
        last.setReady(from.isReady());
        last.setTotalMessagesSent(newModifications.size());
        return newModifications;
    }

    private void handleCanCommit(final CohortEntry cohortEntry) {
        cohortEntry.canCommit(new FutureCallback<Void>() {
            @Override
            public void onSuccess(final Void result) {
                log.debug("{}: canCommit for {}: success", name, cohortEntry.getTransactionID());

                if (cohortEntry.isDoImmediateCommit()) {
                    doCommit(cohortEntry);
                } else {
                    cohortEntry.getReplySender().tell(
                        CanCommitTransactionReply.yes(cohortEntry.getClientVersion()).toSerializable(),
                        cohortEntry.getShard().self());
                }
            }

            @Override
            public void onFailure(final Throwable t) {
                log.debug("{}: An exception occurred during canCommit for {}: {}", name,
                        cohortEntry.getTransactionID(), t);

                cohortCache.remove(cohortEntry.getTransactionID());
                cohortEntry.getReplySender().tell(new Failure(t), cohortEntry.getShard().self());
            }
        });
    }

    /**
     * This method handles the canCommit phase for a transaction.
     *
     * @param transactionID the ID of the transaction to canCommit
     * @param sender the actor to which to send the response
     * @param shard the transaction's shard actor
     */
    void handleCanCommit(final Identifier transactionID, final ActorRef sender, final Shard shard) {
        // Lookup the cohort entry that was cached previously (or should have been) by
        // transactionReady (via the ForwardedReadyTransaction message).
        final CohortEntry cohortEntry = cohortCache.get(transactionID);
        if (cohortEntry == null) {
            // Either canCommit was invoked before ready (shouldn't happen) or a long time passed
            // between canCommit and ready and the entry was expired from the cache or it was aborted.
            IllegalStateException ex = new IllegalStateException(
                    String.format("%s: Cannot canCommit transaction %s - no cohort entry found", name, transactionID));
            log.error(ex.getMessage());
            sender.tell(new Failure(ex), shard.self());
            return;
        }

        cohortEntry.setReplySender(sender);
        cohortEntry.setShard(shard);

        handleCanCommit(cohortEntry);
    }

    private void doCommit(final CohortEntry cohortEntry) {
        log.debug("{}: Committing transaction {}", name, cohortEntry.getTransactionID());

        // We perform the preCommit phase here atomically with the commit phase. This is an
        // optimization to eliminate the overhead of an extra preCommit message. We lose front-end
        // coordination of preCommit across shards in case of failure but preCommit should not
        // normally fail since we ensure only one concurrent 3-phase commit.
        cohortEntry.preCommit(new FutureCallback<DataTreeCandidate>() {
            @Override
            public void onSuccess(final DataTreeCandidate candidate) {
                finishCommit(cohortEntry.getReplySender(), cohortEntry);
            }

            @Override
            public void onFailure(final Throwable t) {
                log.error("{} An exception occurred while preCommitting transaction {}", name,
                        cohortEntry.getTransactionID(), t);

                cohortCache.remove(cohortEntry.getTransactionID());
                cohortEntry.getReplySender().tell(new Failure(t), cohortEntry.getShard().self());
            }
        });
    }

    private void finishCommit(@Nonnull final ActorRef sender, @Nonnull final CohortEntry cohortEntry) {
        log.debug("{}: Finishing commit for transaction {}", persistenceId(), cohortEntry.getTransactionID());

        cohortEntry.commit(new FutureCallback<UnsignedLong>() {
            @Override
            public void onSuccess(final UnsignedLong result) {
                final TransactionIdentifier txId = cohortEntry.getTransactionID();
                log.debug("{}: Transaction {} committed as {}, sending response to {}", persistenceId(), txId, result,
                    sender);

                cohortCache.remove(cohortEntry.getTransactionID());
                sender.tell(CommitTransactionReply.instance(cohortEntry.getClientVersion()).toSerializable(),
                    cohortEntry.getShard().self());
            }

            @Override
            public void onFailure(final Throwable t) {
                log.error("{}, An exception occurred while committing transaction {}", persistenceId(),
                        cohortEntry.getTransactionID(), t);

                cohortCache.remove(cohortEntry.getTransactionID());
                sender.tell(new Failure(t), cohortEntry.getShard().self());
            }
        });
    }

    /**
     * This method handles the preCommit and commit phases for a transaction.
     *
     * @param transactionID the ID of the transaction to commit
     * @param sender the actor to which to send the response
     * @param shard the transaction's shard actor
     */
    void handleCommit(final Identifier transactionID, final ActorRef sender, final Shard shard) {
        final CohortEntry cohortEntry = cohortCache.get(transactionID);
        if (cohortEntry == null) {
            // Either a long time passed between canCommit and commit and the entry was expired from the cache
            // or it was aborted.
            IllegalStateException ex = new IllegalStateException(
                    String.format("%s: Cannot commit transaction %s - no cohort entry found", name, transactionID));
            log.error(ex.getMessage());
            sender.tell(new Failure(ex), shard.self());
            return;
        }

        cohortEntry.setReplySender(sender);
        doCommit(cohortEntry);
    }

    void handleAbort(final Identifier transactionID, final ActorRef sender, final Shard shard) {
        CohortEntry cohortEntry = cohortCache.remove(transactionID);
        if (cohortEntry == null) {
            return;
        }

        log.debug("{}: Aborting transaction {}", name, transactionID);

        final ActorRef self = shard.getSelf();
        try {
            cohortEntry.abort();

            shard.getShardMBean().incrementAbortTransactionsCount();

            if (sender != null) {
                sender.tell(AbortTransactionReply.instance(cohortEntry.getClientVersion()).toSerializable(), self);
            }
        } catch (Exception e) {
            log.error("{}: An exception happened during abort", name, e);

            if (sender != null) {
                sender.tell(new Failure(e), self);
            }
        }
    }

    void checkForExpiredTransactions(final long timeout, final Shard shard) {
        Iterator<CohortEntry> iter = cohortCache.values().iterator();
        while (iter.hasNext()) {
            CohortEntry cohortEntry = iter.next();
            if(cohortEntry.isFailed()) {
                iter.remove();
            }
        }
    }

    void abortPendingTransactions(final String reason, final Shard shard) {
        final Failure failure = new Failure(new RuntimeException(reason));
        Collection<ShardDataTreeCohort> pending = dataTree.getAndClearPendingTransactions();

        log.debug("{}: Aborting {} pending queued transactions", name, pending.size());

        for (ShardDataTreeCohort cohort : pending) {
            CohortEntry cohortEntry = cohortCache.remove(cohort.getIdentifier());
            if (cohortEntry == null) {
                continue;
            }

            if (cohortEntry.getReplySender() != null) {
                cohortEntry.getReplySender().tell(failure, shard.self());
            }
        }

        cohortCache.clear();
    }

    Collection<?> convertPendingTransactionsToMessages(final int maxModificationsPerBatch) {
        final Collection<VersionedExternalizableMessage> messages = new ArrayList<>();
        for (ShardDataTreeCohort cohort : dataTree.getAndClearPendingTransactions()) {
            CohortEntry cohortEntry = cohortCache.remove(cohort.getIdentifier());
            if (cohortEntry == null) {
                continue;
            }

            final Deque<BatchedModifications> newMessages = new ArrayDeque<>();
            cohortEntry.getDataTreeModification().applyToCursor(new AbstractBatchedModificationsCursor() {
                @Override
                protected BatchedModifications getModifications() {
                    final BatchedModifications lastBatch = newMessages.peekLast();

                    if (lastBatch != null && lastBatch.getModifications().size() >= maxModificationsPerBatch) {
                        return lastBatch;
                    }

                    // Allocate a new message
                    final BatchedModifications ret = new BatchedModifications(cohortEntry.getTransactionID(),
                        cohortEntry.getClientVersion());
                    newMessages.add(ret);
                    return ret;
                }
            });

            final BatchedModifications last = newMessages.peekLast();
            if (last != null) {
                final boolean immediate = cohortEntry.isDoImmediateCommit();
                last.setDoCommitOnReady(immediate);
                last.setReady(true);
                last.setTotalMessagesSent(newMessages.size());

                messages.addAll(newMessages);

                if (!immediate) {
                    switch (cohort.getState()) {
                        case CAN_COMMIT_COMPLETE:
                        case CAN_COMMIT_PENDING:
                            messages.add(new CanCommitTransaction(cohortEntry.getTransactionID(),
                                cohortEntry.getClientVersion()));
                            break;
                        case PRE_COMMIT_COMPLETE:
                        case PRE_COMMIT_PENDING:
                            messages.add(new CommitTransaction(cohortEntry.getTransactionID(),
                                cohortEntry.getClientVersion()));
                            break;
                        default:
                            break;
                    }
                }
            }
        }

        return messages;
    }

    @VisibleForTesting
    void setCohortDecorator(final CohortDecorator cohortDecorator) {
        this.cohortDecorator = cohortDecorator;
    }
}