/*
 * Copyright (c) 2016 Cisco 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.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.common.collect.Range;
import com.google.common.collect.RangeSet;
import com.google.common.collect.TreeRangeSet;
import com.google.common.primitives.UnsignedLong;
import java.util.HashMap;
import java.util.Map;
import javax.annotation.Nullable;
import javax.annotation.concurrent.NotThreadSafe;
import org.opendaylight.controller.cluster.access.commands.CreateLocalHistoryRequest;
import org.opendaylight.controller.cluster.access.commands.DeadHistoryException;
import org.opendaylight.controller.cluster.access.commands.DestroyLocalHistoryRequest;
import org.opendaylight.controller.cluster.access.commands.LocalHistoryRequest;
import org.opendaylight.controller.cluster.access.commands.LocalHistorySuccess;
import org.opendaylight.controller.cluster.access.commands.OutOfOrderRequestException;
import org.opendaylight.controller.cluster.access.commands.PurgeLocalHistoryRequest;
import org.opendaylight.controller.cluster.access.commands.TransactionRequest;
import org.opendaylight.controller.cluster.access.commands.TransactionSuccess;
import org.opendaylight.controller.cluster.access.commands.UnknownHistoryException;
import org.opendaylight.controller.cluster.access.concepts.ClientIdentifier;
import org.opendaylight.controller.cluster.access.concepts.LocalHistoryIdentifier;
import org.opendaylight.controller.cluster.access.concepts.RequestEnvelope;
import org.opendaylight.controller.cluster.access.concepts.RequestException;
import org.opendaylight.controller.cluster.access.concepts.UnsupportedRequestException;
import org.opendaylight.yangtools.concepts.Identifiable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Frontend state as observed by the shard leader. This class is responsible for tracking generations and sequencing
 * in the frontend/backend conversation.
 *
 * @author Robert Varga
 */
@NotThreadSafe
final class LeaderFrontendState implements Identifiable<ClientIdentifier> {
    private static final Logger LOG = LoggerFactory.getLogger(LeaderFrontendState.class);

    // Histories which have not been purged
    private final Map<LocalHistoryIdentifier, LocalFrontendHistory> localHistories;

    // RangeSet performs automatic merging, hence we keep minimal state tracking information
    private final RangeSet<UnsignedLong> purgedHistories;

    // Used for all standalone transactions
    private final AbstractFrontendHistory standaloneHistory;
    private final ShardDataTree tree;
    private final ClientIdentifier clientId;
    private final String persistenceId;

    private long expectedTxSequence;
    private Long lastSeenHistory = null;

    // TODO: explicit failover notification
    //       Record the ActorRef for the originating actor and when we switch to being a leader send a notification
    //       to the frontend client -- that way it can immediately start sending requests

    // TODO: add statistics:
    // - number of requests processed
    // - number of histories processed
    // - per-RequestException throw counters

    LeaderFrontendState(final String persistenceId, final ClientIdentifier clientId, final ShardDataTree tree) {
        this(persistenceId, clientId, tree, TreeRangeSet.create(), StandaloneFrontendHistory.create(persistenceId,
            clientId, tree), new HashMap<>());
    }

    LeaderFrontendState(final String persistenceId, final ClientIdentifier clientId, final ShardDataTree tree,
        final RangeSet<UnsignedLong> purgedHistories, final AbstractFrontendHistory standaloneHistory,
        final Map<LocalHistoryIdentifier, LocalFrontendHistory> localHistories) {
        this.persistenceId = Preconditions.checkNotNull(persistenceId);
        this.clientId = Preconditions.checkNotNull(clientId);
        this.tree = Preconditions.checkNotNull(tree);
        this.purgedHistories = Preconditions.checkNotNull(purgedHistories);
        this.standaloneHistory = Preconditions.checkNotNull(standaloneHistory);
        this.localHistories = Preconditions.checkNotNull(localHistories);
    }

    @Override
    public ClientIdentifier getIdentifier() {
        return clientId;
    }

    private void checkRequestSequence(final RequestEnvelope envelope) throws OutOfOrderRequestException {
        if (expectedTxSequence != envelope.getTxSequence()) {
            throw new OutOfOrderRequestException(expectedTxSequence);
        }
    }

    private void expectNextRequest() {
        expectedTxSequence++;
    }

    @Nullable LocalHistorySuccess handleLocalHistoryRequest(final LocalHistoryRequest<?> request,
            final RequestEnvelope envelope, final long now) throws RequestException {
        checkRequestSequence(envelope);

        try {
            if (request instanceof CreateLocalHistoryRequest) {
                return handleCreateHistory((CreateLocalHistoryRequest) request);
            } else if (request instanceof DestroyLocalHistoryRequest) {
                return handleDestroyHistory((DestroyLocalHistoryRequest) request, envelope, now);
            } else if (request instanceof PurgeLocalHistoryRequest) {
                return handlePurgeHistory((PurgeLocalHistoryRequest)request, envelope, now);
            } else {
                throw new UnsupportedRequestException(request);
            }
        } finally {
            expectNextRequest();
        }
    }

    private LocalHistorySuccess handleCreateHistory(final CreateLocalHistoryRequest request) throws RequestException {
        final LocalHistoryIdentifier id = request.getTarget();
        final AbstractFrontendHistory existing = localHistories.get(id);
        if (existing != null) {
            // History already exists: report success
            LOG.debug("{}: history {} already exists", persistenceId, id);
            return new LocalHistorySuccess(id, request.getSequence());
        }

        // We have not found the history. Before we create it we need to check history ID sequencing so that we do not
        // end up resurrecting a purged history.
        if (purgedHistories.contains(UnsignedLong.fromLongBits(id.getHistoryId()))) {
            LOG.debug("{}: rejecting purged request {}", persistenceId, request);
            throw new DeadHistoryException(lastSeenHistory.longValue());
        }

        // Update last history we have seen
        if (lastSeenHistory != null && Long.compareUnsigned(lastSeenHistory, id.getHistoryId()) < 0) {
            lastSeenHistory = id.getHistoryId();
        }

        localHistories.put(id, LocalFrontendHistory.create(persistenceId, tree, id));
        LOG.debug("{}: created history {}", persistenceId, id);
        return new LocalHistorySuccess(id, request.getSequence());
    }

    private LocalHistorySuccess handleDestroyHistory(final DestroyLocalHistoryRequest request,
            final RequestEnvelope envelope, final long now)
            throws RequestException {
        final LocalHistoryIdentifier id = request.getTarget();
        final LocalFrontendHistory existing = localHistories.get(id);
        if (existing == null) {
            // History does not exist: report success
            LOG.debug("{}: history {} does not exist, nothing to destroy", persistenceId, id);
            return new LocalHistorySuccess(id, request.getSequence());
        }

        existing.destroy(request.getSequence(), envelope, now);
        return null;
    }

    private LocalHistorySuccess handlePurgeHistory(final PurgeLocalHistoryRequest request,
            final RequestEnvelope envelope, final long now) throws RequestException {
        final LocalHistoryIdentifier id = request.getTarget();
        final LocalFrontendHistory existing = localHistories.remove(id);
        if (existing == null) {
            LOG.debug("{}: history {} has already been purged", persistenceId, id);
            return new LocalHistorySuccess(id, request.getSequence());
        }

        LOG.debug("{}: purging history {}", persistenceId, id);
        purgedHistories.add(Range.singleton(UnsignedLong.fromLongBits(id.getHistoryId())));
        existing.purge(request.getSequence(), envelope, now);
        return null;
    }

    @Nullable TransactionSuccess<?> handleTransactionRequest(final TransactionRequest<?> request,
            final RequestEnvelope envelope, final long now) throws RequestException {
        checkRequestSequence(envelope);

        try {
            final LocalHistoryIdentifier lhId = request.getTarget().getHistoryId();
            final AbstractFrontendHistory history;

            if (lhId.getHistoryId() != 0) {
                history = localHistories.get(lhId);
                if (history == null) {
                    LOG.debug("{}: rejecting unknown history request {}", persistenceId, request);
                    throw new UnknownHistoryException(lastSeenHistory);
                }
            } else {
                history = standaloneHistory;
            }

            return history.handleTransactionRequest(request, envelope, now);
        } finally {
            expectNextRequest();
        }
    }

    void reconnect() {
        expectedTxSequence = 0;
    }

    void retire() {
        // FIXME: flush all state
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(LeaderFrontendState.class).add("clientId", clientId)
                .add("purgedHistories", purgedHistories).toString();
    }
}