/*
 * Copyright (c) 2015 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.entityownership;

import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.CANDIDATE_NAME_NODE_ID;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.CANDIDATE_NODE_ID;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_NODE_ID;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNERS_PATH;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_NODE_ID;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_QNAME;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPES_PATH;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidatePath;
import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.entityOwnersWithCandidate;
import akka.actor.ActorRef;
import akka.actor.ActorSelection;
import akka.actor.Props;
import akka.pattern.Patterns;
import com.google.common.base.Optional;
import com.google.common.base.Strings;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import org.opendaylight.controller.cluster.datastore.DatastoreContext;
import org.opendaylight.controller.cluster.datastore.Shard;
import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateAdded;
import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateRemoved;
import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterCandidateLocal;
import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
import org.opendaylight.controller.md.sal.common.api.clustering.Entity;
import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeSnapshot;
import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
import org.opendaylight.yangtools.yang.model.api.SchemaContext;
import scala.concurrent.Future;

/**
 * Special Shard for EntityOwnership.
 *
 * @author Thomas Pantelis
 */
class EntityOwnershipShard extends Shard {
    private final String localMemberName;
    private final EntityOwnershipShardCommitCoordinator commitCoordinator;
    private final EntityOwnershipListenerSupport listenerSupport;
    private final Set<String> downPeerMemberNames = new HashSet<>();
    private final Map<String, String> peerIdToMemberNames = new HashMap<>();

    private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
        return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
    }

    protected EntityOwnershipShard(ShardIdentifier name, Map<String, String> peerAddresses,
            DatastoreContext datastoreContext, SchemaContext schemaContext, String localMemberName) {
        super(name, peerAddresses, noPersistenceDatastoreContext(datastoreContext), schemaContext);
        this.localMemberName = localMemberName;
        this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(localMemberName, LOG);
        this.listenerSupport = new EntityOwnershipListenerSupport(getContext());

        for(String peerId: peerAddresses.keySet()) {
            ShardIdentifier shardId = ShardIdentifier.builder().fromShardIdString(peerId).build();
            peerIdToMemberNames.put(peerId, shardId.getMemberName());
        }
    }

    @Override
    protected void onDatastoreContext(DatastoreContext context) {
        super.onDatastoreContext(noPersistenceDatastoreContext(context));
    }

    @Override
    protected void onRecoveryComplete() {
        super.onRecoveryComplete();

        new CandidateListChangeListener(getSelf()).init(getDataStore());
        new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
    }

    @Override
    public void onReceiveCommand(final Object message) throws Exception {
        if(message instanceof RegisterCandidateLocal) {
            onRegisterCandidateLocal((RegisterCandidateLocal)message);
        } else if(message instanceof UnregisterCandidateLocal) {
            onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
        } else if(message instanceof CandidateAdded){
            onCandidateAdded((CandidateAdded) message);
        } else if(message instanceof CandidateRemoved){
            onCandidateRemoved((CandidateRemoved) message);
        } else if(message instanceof PeerDown) {
            onPeerDown((PeerDown) message);
        } else if(message instanceof PeerUp) {
            onPeerUp((PeerUp) message);
        } else if(!commitCoordinator.handleMessage(message, this)) {
            super.onReceiveCommand(message);
        }
    }

    private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
        LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);

        listenerSupport.addEntityOwnershipListener(registerCandidate.getEntity(), registerCandidate.getCandidate());

        NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
                registerCandidate.getEntity().getId(), localMemberName);
        commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);

        getSender().tell(SuccessReply.INSTANCE, getSelf());
    }

    private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
        LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);

        Entity entity = unregisterCandidate.getEntity();
        listenerSupport.removeEntityOwnershipListener(entity, unregisterCandidate.getCandidate());

        YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
        commitCoordinator.commitModification(new DeleteModification(candidatePath), this);

        getSender().tell(SuccessReply.INSTANCE, getSelf());
    }

    void tryCommitModifications(final BatchedModifications modifications) {
        if(isLeader()) {
            LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());

            // Note that it's possible the commit won't get consensus and will timeout and not be applied
            // to the state. However we don't need to retry it in that case b/c it will be committed to
            // the journal first and, once a majority of followers come back on line and it is replicated,
            // it will be applied at that point.
            handleBatchedModificationsLocal(modifications, self());
        } else {
            final ActorSelection leader = getLeader();
            if (leader != null) {
                if(LOG.isDebugEnabled()) {
                    LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
                            modifications.getTransactionID(), leader);
                }

                Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
                        getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));

                Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
            }
        }
    }

    boolean hasLeader() {
        return getLeader() != null && !isIsolatedLeader();
    }

    @Override
    protected void onStateChanged() {
        super.onStateChanged();

        commitCoordinator.onStateChanged(this, isLeader());
    }

    @Override
    protected void onLeaderChanged(String oldLeader, String newLeader) {
        super.onLeaderChanged(oldLeader, newLeader);

        LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
                newLeader, isLeader());

        if(isLeader()) {
            // We were just elected leader. If the old leader is down, select new owners for the entities
            // owned by the down leader.

            String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);

            LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);

            if(downPeerMemberNames.contains(oldLeaderMemberName)) {
                selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
            }
        }
    }

    private void onCandidateRemoved(CandidateRemoved message) {
        if(!isLeader()) {
            return;
        }

        LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);

        String currentOwner = getCurrentOwner(message.getEntityPath());
        if(message.getRemovedCandidate().equals(currentOwner)){
            writeNewOwner(message.getEntityPath(), newOwner(message.getRemainingCandidates()));
        }
    }

    private void onCandidateAdded(CandidateAdded message) {
        if(!isLeader()){
            return;
        }

        LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);

        String currentOwner = getCurrentOwner(message.getEntityPath());
        if(Strings.isNullOrEmpty(currentOwner)){
            writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates()));
        }
    }

    private void onPeerDown(PeerDown peerDown) {
        LOG.debug("{}: onPeerDown: {}", persistenceId(), peerDown);

        String downMemberName = peerDown.getMemberName();
        if(downPeerMemberNames.add(downMemberName) && isLeader()) {
            // Select new owners for entities owned by the down peer.
            selectNewOwnerForEntitiesOwnedBy(downMemberName);
        }
    }

    private void onPeerUp(PeerUp peerUp) {
        LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);

        peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());

        if(downPeerMemberNames.remove(peerUp.getMemberName()) && isLeader()) {
            // This peer was previously down - for its previously owned entities, if there were no other
            // candidates, the owner would have been cleared so handle that here by trying to re-assign
            // ownership for entities whose owner is cleared.
            selectNewOwnerForEntitiesOwnedBy("");
        }
    }

    private void selectNewOwnerForEntitiesOwnedBy(String owner) {
        DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
        Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
        if(!possibleEntityTypes.isPresent()) {
            return;
        }

        LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);

        BatchedModifications modifications = commitCoordinator.newBatchedModifications();
        for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
            Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
                    entityType.getChild(ENTITY_NODE_ID);
            if(!possibleEntities.isPresent()) {
                continue; // shouldn't happen but handle anyway
            }

            for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
                Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
                        entity.getChild(ENTITY_OWNER_NODE_ID);
                if(possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
                    Object newOwner = newOwner(getCandidateNames(entity));
                    YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
                            node(entityType.getIdentifier()).node(ENTITY_NODE_ID).node(entity.getIdentifier()).
                                    node(ENTITY_OWNER_NODE_ID).build();

                    LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);

                    modifications.addModification(new WriteModification(entityPath,
                            ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
                }
            }
        }

        commitCoordinator.commitModifications(modifications, this);
    }

    private Collection<String> getCandidateNames(MapEntryNode entity) {
        Collection<MapEntryNode> candidates = ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
        Collection<String> candidateNames = new ArrayList<>(candidates.size());
        for(MapEntryNode candidate: candidates) {
            candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
        }

        return candidateNames;
    }

    private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
        LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);

        commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
                ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
    }

    private String newOwner(Collection<String> candidates) {
        for(String candidate: candidates) {
            if(!downPeerMemberNames.contains(candidate)) {
                return candidate;
            }
        }

        return "";
    }

    private String getCurrentOwner(YangInstanceIdentifier entityId) {
        DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
        Optional<NormalizedNode<?, ?>> optionalEntityOwner = snapshot.readNode(entityId.node(ENTITY_OWNER_QNAME));
        if(optionalEntityOwner.isPresent()){
            return optionalEntityOwner.get().getValue().toString();
        }
        return null;
    }

    public static Props props(final ShardIdentifier name, final Map<String, String> peerAddresses,
            final DatastoreContext datastoreContext, final SchemaContext schemaContext, final String localMemberName) {
        return Props.create(new Creator(name, peerAddresses, datastoreContext, schemaContext, localMemberName));
    }

    private static class Creator extends AbstractShardCreator {
        private static final long serialVersionUID = 1L;

        private final String localMemberName;

        Creator(final ShardIdentifier name, final Map<String, String> peerAddresses,
                final DatastoreContext datastoreContext, final SchemaContext schemaContext,
                final String localMemberName) {
            super(name, peerAddresses, datastoreContext, schemaContext);
            this.localMemberName = localMemberName;
        }

        @Override
        public Shard create() throws Exception {
            return new EntityOwnershipShard(name, peerAddresses, datastoreContext, schemaContext, localMemberName);
        }
    }
}