/*
 * 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.sharding;

import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collectors;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
import org.opendaylight.controller.cluster.databroker.actors.dds.DataStoreClient;
import org.opendaylight.controller.cluster.datastore.DistributedDataStore;
import org.opendaylight.mdsal.dom.api.DOMDataTreeChangeListener;
import org.opendaylight.mdsal.dom.api.DOMDataTreeIdentifier;
import org.opendaylight.mdsal.dom.spi.AbstractDOMDataTreeChangeListenerRegistration;
import org.opendaylight.mdsal.dom.spi.AbstractRegistrationTree;
import org.opendaylight.mdsal.dom.spi.RegistrationTreeNode;
import org.opendaylight.mdsal.dom.spi.shard.ChildShardContext;
import org.opendaylight.mdsal.dom.spi.store.DOMStoreTreeChangePublisher;
import org.opendaylight.yangtools.concepts.ListenerRegistration;
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.NormalizedNode;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTree;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidate;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidateNode;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidates;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeModification;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataValidationFailedException;
import org.opendaylight.yangtools.yang.data.api.schema.tree.ModificationType;
import org.opendaylight.yangtools.yang.data.api.schema.tree.TreeType;
import org.opendaylight.yangtools.yang.data.impl.schema.tree.InMemoryDataTreeFactory;
import org.opendaylight.yangtools.yang.data.impl.schema.tree.SchemaValidationFailedException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class DistributedShardChangePublisher
        extends AbstractRegistrationTree<AbstractDOMDataTreeChangeListenerRegistration<?>>
        implements DOMStoreTreeChangePublisher {

    private static final Logger LOG = LoggerFactory.getLogger(DistributedShardChangePublisher.class);

    private final DistributedDataStore distributedDataStore;
    private final YangInstanceIdentifier shardPath;

    // This will be useful for signaling back pressure
    private final DataStoreClient client;

    private final Map<DOMDataTreeIdentifier, ChildShardContext> childShards;

    @GuardedBy("this")
    private final DataTree dataTree;

    public DistributedShardChangePublisher(final DataStoreClient client,
                                           final DistributedDataStore distributedDataStore,
                                           final DOMDataTreeIdentifier prefix,
                                           final Map<DOMDataTreeIdentifier, ChildShardContext> childShards) {
        this.client = client;
        this.distributedDataStore = distributedDataStore;
        // TODO keeping the whole dataTree thats contained in subshards doesn't seem like a good idea
        // maybe the whole listener logic would be better in the backend shards where we have direct access to the
        // dataTree and wont have to cache it redundantly.
        this.dataTree = InMemoryDataTreeFactory.getInstance().create(
                TreeType.valueOf(prefix.getDatastoreType().name()), prefix.getRootIdentifier());

        dataTree.setSchemaContext(distributedDataStore.getActorContext().getSchemaContext());

        this.shardPath = prefix.getRootIdentifier();
        this.childShards = childShards;
    }

    protected void registrationRemoved(final AbstractDOMDataTreeChangeListenerRegistration<?> registration) {
        LOG.debug("Closing registration {}", registration);
    }

    @Override
    public <L extends DOMDataTreeChangeListener> AbstractDOMDataTreeChangeListenerRegistration<L>
            registerTreeChangeListener(final YangInstanceIdentifier path, final L listener) {
        takeLock();
        try {
            return setupListenerContext(path, listener);
        } finally {
            releaseLock();
        }
    }

    private <L extends DOMDataTreeChangeListener> AbstractDOMDataTreeChangeListenerRegistration<L>
            setupListenerContext(final YangInstanceIdentifier listenerPath, final L listener) {
        // we need to register the listener registration path based on the shards root
        // we have to strip the shard path from the listener path and then register
        YangInstanceIdentifier strippedIdentifier = listenerPath;
        if (!shardPath.isEmpty()) {
            strippedIdentifier = YangInstanceIdentifier.create(stripShardPath(shardPath, listenerPath));
        }

        final DOMDataTreeListenerWithSubshards subshardListener =
                new DOMDataTreeListenerWithSubshards(strippedIdentifier, listener);
        final AbstractDOMDataTreeChangeListenerRegistration<L> reg =
                setupContextWithoutSubshards(listenerPath, strippedIdentifier, subshardListener);

        for (final ChildShardContext maybeAffected : childShards.values()) {
            if (listenerPath.contains(maybeAffected.getPrefix().getRootIdentifier())) {
                // consumer has initialDataChangeEvent subshard somewhere on lower level
                // register to the notification manager with snapshot and forward child notifications to parent
                LOG.debug("Adding new subshard{{}} to listener at {}", maybeAffected.getPrefix(), listenerPath);
                subshardListener.addSubshard(maybeAffected);
            } else if (maybeAffected.getPrefix().getRootIdentifier().contains(listenerPath)) {
                // bind path is inside subshard
                // TODO can this happen? seems like in ShardedDOMDataTree we are
                // already registering to the lowest shard possible
                throw new UnsupportedOperationException("Listener should be registered directly "
                        + "into initialDataChangeEvent subshard");
            }
        }

        return reg;
    }

    private <L extends DOMDataTreeChangeListener> AbstractDOMDataTreeChangeListenerRegistration<L>
            setupContextWithoutSubshards(final YangInstanceIdentifier shardLookup,
                                         final YangInstanceIdentifier listenerPath,
                                         final DOMDataTreeListenerWithSubshards listener) {

        LOG.debug("Registering root listener full path: {}, path inside shard: {}", shardLookup, listenerPath);

        // register in the shard tree
        final RegistrationTreeNode<AbstractDOMDataTreeChangeListenerRegistration<?>> node =
                findNodeFor(listenerPath.getPathArguments());

        // register listener in CDS
        final ProxyRegistration proxyReg = new ProxyRegistration(distributedDataStore
                .registerProxyListener(shardLookup, listenerPath, listener), listener);

        @SuppressWarnings("unchecked")
        final AbstractDOMDataTreeChangeListenerRegistration<L> registration =
            new AbstractDOMDataTreeChangeListenerRegistration<L>((L) listener) {
                @Override
                protected void removeRegistration() {
                    listener.close();
                    DistributedShardChangePublisher.this.removeRegistration(node, this);
                    registrationRemoved(this);
                    proxyReg.close();
                }
            };
        addRegistration(node, registration);

        return registration;
    }

    private static Iterable<PathArgument> stripShardPath(final YangInstanceIdentifier shardPath,
                                                         final YangInstanceIdentifier listenerPath) {
        if (shardPath.isEmpty()) {
            return listenerPath.getPathArguments();
        }

        final List<PathArgument> listenerPathArgs = new ArrayList<>(listenerPath.getPathArguments());
        final Iterator<PathArgument> shardIter = shardPath.getPathArguments().iterator();
        final Iterator<PathArgument> listenerIter = listenerPathArgs.iterator();

        while (shardIter.hasNext()) {
            if (shardIter.next().equals(listenerIter.next())) {
                listenerIter.remove();
            } else {
                break;
            }
        }

        return listenerPathArgs;
    }

    private static class ProxyRegistration implements ListenerRegistration<DOMDataTreeChangeListener> {

        private final ListenerRegistration<org.opendaylight.controller.md.sal.dom.api.DOMDataTreeChangeListener> proxy;
        private final DOMDataTreeChangeListener listener;

        private ProxyRegistration(
                final ListenerRegistration<
                        org.opendaylight.controller.md.sal.dom.api.DOMDataTreeChangeListener> proxy,
                final DOMDataTreeChangeListener listener) {
            this.proxy = proxy;
            this.listener = listener;
        }

        @Override
        public DOMDataTreeChangeListener getInstance() {
            return listener;
        }

        @Override
        public void close() {
            proxy.close();
        }
    }

    synchronized DataTreeCandidate applyChanges(final YangInstanceIdentifier listenerPath,
            final Collection<DataTreeCandidate> changes) {
        final DataTreeModification modification = dataTree.takeSnapshot().newModification();
        for (final DataTreeCandidate change : changes) {
            try {
                DataTreeCandidates.applyToModification(modification, change);
            } catch (SchemaValidationFailedException e) {
                LOG.error("Validation failed {}", e);
            }
        }

        modification.ready();

        final DataTreeCandidate candidate;

        try {
            dataTree.validate(modification);
        } catch (final DataValidationFailedException e) {
            LOG.error("Validation failed for built modification, modification {}, current data tree: {}",
                    modification, dataTree, e);
            throw new RuntimeException("Notification validation failed", e);
        }

        // strip nodes we dont need since this listener doesn't have to be registered at the root of the DataTree
        candidate = dataTree.prepare(modification);
        dataTree.commit(candidate);


        DataTreeCandidateNode modifiedChild = candidate.getRootNode();

        for (final PathArgument pathArgument : listenerPath.getPathArguments()) {
            modifiedChild = modifiedChild.getModifiedChild(pathArgument);
        }

        if (modifiedChild == null) {
            modifiedChild = new EmptyDataTreeCandidateNode(dataTree.getRootPath().getLastPathArgument());
        }

        return DataTreeCandidates.newDataTreeCandidate(dataTree.getRootPath(), modifiedChild);
    }


    private final class DOMDataTreeListenerWithSubshards implements DOMDataTreeChangeListener {

        private final YangInstanceIdentifier listenerPath;
        private final DOMDataTreeChangeListener delegate;

        private final Map<YangInstanceIdentifier, ListenerRegistration<DOMDataTreeChangeListener>> registrations =
                new ConcurrentHashMap<>();

        DOMDataTreeListenerWithSubshards(final YangInstanceIdentifier listenerPath,
                                         final DOMDataTreeChangeListener delegate) {
            this.listenerPath = Preconditions.checkNotNull(listenerPath);
            this.delegate = Preconditions.checkNotNull(delegate);
        }

        @Override
        public void onDataTreeChanged(@Nonnull final Collection<DataTreeCandidate> changes) {
            LOG.debug("Received data changed {}", changes);
            applyChanges(listenerPath, changes);
            delegate.onDataTreeChanged(changes);
        }

        synchronized void onDataTreeChanged(final YangInstanceIdentifier pathFromRoot,
                                            final Collection<DataTreeCandidate> changes) {
            final YangInstanceIdentifier changeId =
                    YangInstanceIdentifier.create(stripShardPath(dataTree.getRootPath(), pathFromRoot));

            final List<DataTreeCandidate> newCandidates = changes.stream()
                    .map(candidate -> DataTreeCandidates.newDataTreeCandidate(changeId, candidate.getRootNode()))
                    .collect(Collectors.toList());
            delegate.onDataTreeChanged(Collections.singleton(applyChanges(listenerPath, newCandidates)));
        }

        void addSubshard(final ChildShardContext context) {
            Preconditions.checkState(context.getShard() instanceof DOMStoreTreeChangePublisher,
                    "All subshards that are initialDataChangeEvent part of ListenerContext need to be listenable");

            final DOMStoreTreeChangePublisher listenableShard = (DOMStoreTreeChangePublisher) context.getShard();
            // since this is going into subshard we want to listen for ALL changes in the subshard
            registrations.put(context.getPrefix().getRootIdentifier(),
                    listenableShard.registerTreeChangeListener(
                            context.getPrefix().getRootIdentifier(), changes -> onDataTreeChanged(
                                    context.getPrefix().getRootIdentifier(), changes)));
        }

        void close() {
            for (final ListenerRegistration<DOMDataTreeChangeListener> registration : registrations.values()) {
                registration.close();
            }
            registrations.clear();
        }
    }

    private static final class EmptyDataTreeCandidateNode implements DataTreeCandidateNode {

        private final PathArgument identifier;

        EmptyDataTreeCandidateNode(final PathArgument identifier) {
            this.identifier = Preconditions.checkNotNull(identifier, "Identifier should not be null");
        }

        @Nonnull
        @Override
        public PathArgument getIdentifier() {
            return identifier;
        }

        @Nonnull
        @Override
        public Collection<DataTreeCandidateNode> getChildNodes() {
            return Collections.emptySet();
        }

        @Nullable
        @Override
        public DataTreeCandidateNode getModifiedChild(final PathArgument identifier) {
            return null;
        }

        @Nonnull
        @Override
        public ModificationType getModificationType() {
            return ModificationType.UNMODIFIED;
        }

        @Nonnull
        @Override
        public Optional<NormalizedNode<?, ?>> getDataAfter() {
            return Optional.absent();
        }

        @Nonnull
        @Override
        public Optional<NormalizedNode<?, ?>> getDataBefore() {
            return Optional.absent();
        }
    }
}