/*
 * Copyright (c) 2014 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.md.sal.dom.store.impl;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static org.opendaylight.controller.md.sal.dom.store.impl.StoreUtils.increase;

import java.util.Collections;
import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;

import org.opendaylight.controller.md.sal.common.api.data.AsyncDataBroker.DataChangeScope;
import org.opendaylight.controller.md.sal.common.api.data.AsyncDataChangeListener;
import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree;
import org.opendaylight.controller.md.sal.dom.store.impl.tree.ModificationType;
import org.opendaylight.controller.md.sal.dom.store.impl.tree.NodeModification;
import org.opendaylight.controller.md.sal.dom.store.impl.tree.StoreMetadataNode;
import org.opendaylight.controller.sal.core.spi.data.DOMStore;
import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadTransaction;
import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadWriteTransaction;
import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
import org.opendaylight.controller.sal.core.spi.data.DOMStoreTransaction;
import org.opendaylight.controller.sal.core.spi.data.DOMStoreWriteTransaction;
import org.opendaylight.yangtools.concepts.AbstractListenerRegistration;
import org.opendaylight.yangtools.concepts.Identifiable;
import org.opendaylight.yangtools.concepts.ListenerRegistration;
import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier;
import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.PathArgument;
import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
import org.opendaylight.yangtools.yang.data.impl.schema.NormalizedNodeUtils;
import org.opendaylight.yangtools.yang.model.api.SchemaContext;
import org.opendaylight.yangtools.yang.model.api.SchemaContextListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Objects;
import com.google.common.base.Objects.ToStringHelper;
import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import com.google.common.primitives.UnsignedLong;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;

public class InMemoryDOMDataStore implements DOMStore, Identifiable<String>, SchemaContextListener {

    private static final Logger LOG = LoggerFactory.getLogger(InMemoryDOMDataStore.class);
    private static final InstanceIdentifier PUBLIC_ROOT_PATH = InstanceIdentifier.builder().build();


    private final ListeningExecutorService executor;
    private final String name;
    private final AtomicLong txCounter = new AtomicLong(0);
    private final ListenerTree listenerTree;
    private final AtomicReference<DataAndMetadataSnapshot> snapshot;

    private ModificationApplyOperation operationTree;

    private SchemaContext schemaContext;

    public InMemoryDOMDataStore(final String name, final ListeningExecutorService executor) {
        this.name = Preconditions.checkNotNull(name);
        this.executor = Preconditions.checkNotNull(executor);
        this.listenerTree = ListenerTree.create();
        this.snapshot = new AtomicReference<DataAndMetadataSnapshot>(DataAndMetadataSnapshot.createEmpty());
        this.operationTree = new AlwaysFailOperation();
    }

    @Override
    public final String getIdentifier() {
        return name;
    }

    @Override
    public DOMStoreReadTransaction newReadOnlyTransaction() {
        return new SnapshotBackedReadTransaction(nextIdentifier(), snapshot.get());
    }

    @Override
    public DOMStoreReadWriteTransaction newReadWriteTransaction() {
        return new SnapshotBackedReadWriteTransaction(nextIdentifier(), snapshot.get(), this, operationTree);
    }

    @Override
    public DOMStoreWriteTransaction newWriteOnlyTransaction() {
        return new SnaphostBackedWriteTransaction(nextIdentifier(), snapshot.get(), this, operationTree);
    }

    @Override
    public synchronized void onGlobalContextUpdated(final SchemaContext ctx) {
        operationTree = SchemaAwareApplyOperationRoot.from(ctx);
        schemaContext = ctx;
    }

    @Override
    public <L extends AsyncDataChangeListener<InstanceIdentifier, NormalizedNode<?, ?>>> ListenerRegistration<L> registerChangeListener(
            final InstanceIdentifier path, final L listener, final DataChangeScope scope) {

        /*
         * Make sure commit is not occurring right now. Listener has to be registered and its
         * state capture enqueued at a consistent point.
         *
         * FIXME: improve this to read-write lock, such that multiple listener registrations
         *        can occur simultaneously
         */
        final DataChangeListenerRegistration<L> reg;
        synchronized (this) {
            LOG.debug("{}: Registering data change listener {} for {}",name,listener,path);

            reg = listenerTree.registerDataChangeListener(path, listener, scope);

            Optional<StoreMetadataNode> currentState = snapshot.get().read(path);
            if (currentState.isPresent()) {
                final NormalizedNode<?, ?> data = currentState.get().getData();

                final DOMImmutableDataChangeEvent event = DOMImmutableDataChangeEvent.builder(DataChangeScope.BASE) //
                        .setAfter(data) //
                        .addCreated(path, data) //
                        .build();
                executor.submit(new ChangeListenerNotifyTask(Collections.singletonList(reg), event));
            }
        }

        return new AbstractListenerRegistration<L>(listener) {
            @Override
            protected void removeRegistration() {
                synchronized (InMemoryDOMDataStore.this) {
                    reg.close();
                }
            }
        };
    }

    private synchronized DOMStoreThreePhaseCommitCohort submit(
            final SnaphostBackedWriteTransaction writeTx) {
        LOG.debug("Tx: {} is submitted. Modifications: {}",writeTx.getIdentifier(),writeTx.getMutatedView());
        return new ThreePhaseCommitImpl(writeTx);
    }

    private Object nextIdentifier() {
        return name + "-" + txCounter.getAndIncrement();
    }

    private void commit(final DataAndMetadataSnapshot currentSnapshot,
            final StoreMetadataNode newDataTree, final ResolveDataChangeEventsTask listenerResolver) {
        LOG.debug("Updating Store snaphot version: {} with version:{}",currentSnapshot.getMetadataTree().getSubtreeVersion(),newDataTree.getSubtreeVersion());

        if(LOG.isTraceEnabled()) {
            LOG.trace("Data Tree is {}",StoreUtils.toStringTree(newDataTree));
        }

        final DataAndMetadataSnapshot newSnapshot = DataAndMetadataSnapshot.builder() //
                .setMetadataTree(newDataTree) //
                .setSchemaContext(schemaContext) //
                .build();

        /*
         * The commit has to occur atomically with regard to listener registrations.
         */
        synchronized (this) {
            final boolean success = snapshot.compareAndSet(currentSnapshot, newSnapshot);
            checkState(success, "Store snapshot and transaction snapshot differ. This should never happen.");

            for (ChangeListenerNotifyTask task : listenerResolver.call()) {
                executor.submit(task);
            }
        }
    }

    private static abstract class AbstractDOMStoreTransaction implements DOMStoreTransaction {
        private final Object identifier;

        protected AbstractDOMStoreTransaction(final Object identifier) {
            this.identifier = identifier;
        }

        @Override
        public final Object getIdentifier() {
            return identifier;
        }

        @Override
        public final String toString() {
            return addToStringAttributes(Objects.toStringHelper(this)).toString();
        }

        /**
         * Add class-specific toString attributes.
         *
         * @param toStringHelper ToStringHelper instance
         * @return ToStringHelper instance which was passed in
         */
        protected ToStringHelper addToStringAttributes(final ToStringHelper toStringHelper) {
            return toStringHelper.add("id", identifier);
        }
    }

    private static class SnapshotBackedReadTransaction extends AbstractDOMStoreTransaction implements DOMStoreReadTransaction {
        private DataAndMetadataSnapshot stableSnapshot;

        public SnapshotBackedReadTransaction(final Object identifier, final DataAndMetadataSnapshot snapshot) {
            super(identifier);
            this.stableSnapshot = Preconditions.checkNotNull(snapshot);
            LOG.debug("ReadOnly Tx: {} allocated with snapshot {}", identifier, snapshot.getMetadataTree().getSubtreeVersion());
        }

        @Override
        public void close() {
            LOG.debug("Store transaction: {} : Closed", getIdentifier());
            stableSnapshot = null;
        }

        @Override
        public ListenableFuture<Optional<NormalizedNode<?, ?>>> read(final InstanceIdentifier path) {
            checkNotNull(path, "Path must not be null.");
            checkState(stableSnapshot != null, "Transaction is closed");
            return Futures.immediateFuture(NormalizedNodeUtils.findNode(stableSnapshot.getDataTree(), path));
        }
    }

    private static class SnaphostBackedWriteTransaction extends AbstractDOMStoreTransaction implements DOMStoreWriteTransaction {
        private MutableDataTree mutableTree;
        private InMemoryDOMDataStore store;
        private boolean ready = false;

        public SnaphostBackedWriteTransaction(final Object identifier, final DataAndMetadataSnapshot snapshot,
                final InMemoryDOMDataStore store, final ModificationApplyOperation applyOper) {
            super(identifier);
            mutableTree = MutableDataTree.from(snapshot, applyOper);
            this.store = store;
            LOG.debug("Write Tx: {} allocated with snapshot {}",identifier,snapshot.getMetadataTree().getSubtreeVersion());
        }

        @Override
        public void close() {
            LOG.debug("Store transaction: {} : Closed", getIdentifier());
            this.mutableTree = null;
            this.store = null;
        }

        @Override
        public void write(final InstanceIdentifier path, final NormalizedNode<?, ?> data) {
            checkNotReady();
            mutableTree.write(path, data);
        }

        @Override
        public void delete(final InstanceIdentifier path) {
            checkNotReady();
            mutableTree.delete(path);
        }

        protected final boolean isReady() {
            return ready;
        }

        protected final void checkNotReady() {
            checkState(!ready, "Transaction %s is ready. No further modifications allowed.", getIdentifier());
        }

        @Override
        public synchronized DOMStoreThreePhaseCommitCohort ready() {
            checkState(!ready, "Transaction %s is already ready.", getIdentifier());
            ready = true;

            LOG.debug("Store transaction: {} : Ready", getIdentifier());
            mutableTree.seal();
            return store.submit(this);
        }

        protected MutableDataTree getMutatedView() {
            return mutableTree;
        }

        @Override
        protected ToStringHelper addToStringAttributes(final ToStringHelper toStringHelper) {
            return toStringHelper.add("ready", isReady());
        }
    }

    private static class SnapshotBackedReadWriteTransaction extends SnaphostBackedWriteTransaction implements
            DOMStoreReadWriteTransaction {

        protected SnapshotBackedReadWriteTransaction(final Object identifier, final DataAndMetadataSnapshot snapshot,
                final InMemoryDOMDataStore store, final ModificationApplyOperation applyOper) {
            super(identifier, snapshot, store, applyOper);
        }

        @Override
        public ListenableFuture<Optional<NormalizedNode<?, ?>>> read(final InstanceIdentifier path) {
            return Futures.immediateFuture(getMutatedView().read(path));
        }
    }

    private class ThreePhaseCommitImpl implements DOMStoreThreePhaseCommitCohort {

        private final SnaphostBackedWriteTransaction transaction;
        private final NodeModification modification;

        private DataAndMetadataSnapshot storeSnapshot;
        private Optional<StoreMetadataNode> proposedSubtree;
        private ResolveDataChangeEventsTask listenerResolver;

        public ThreePhaseCommitImpl(final SnaphostBackedWriteTransaction writeTransaction) {
            this.transaction = writeTransaction;
            this.modification = transaction.getMutatedView().getRootModification();
        }

        @Override
        public ListenableFuture<Boolean> canCommit() {
            final DataAndMetadataSnapshot snapshotCapture = snapshot.get();
            final ModificationApplyOperation snapshotOperation = operationTree;

            return executor.submit(new Callable<Boolean>() {

                @Override
                public Boolean call() throws Exception {
                    boolean applicable = snapshotOperation.isApplicable(modification,
                            Optional.of(snapshotCapture.getMetadataTree()));
                    LOG.debug("Store Transcation: {} : canCommit : {}", transaction.getIdentifier(), applicable);
                    return applicable;
                }
            });
        }

        @Override
        public ListenableFuture<Void> preCommit() {
            storeSnapshot = snapshot.get();
            if(modification.getModificationType() == ModificationType.UNMODIFIED) {
                return Futures.immediateFuture(null);
            }
            return executor.submit(new Callable<Void>() {



                @Override
                public Void call() throws Exception {
                    StoreMetadataNode metadataTree = storeSnapshot.getMetadataTree();

                    proposedSubtree = operationTree.apply(modification, Optional.of(metadataTree),
                            increase(metadataTree.getSubtreeVersion()));

                    listenerResolver = ResolveDataChangeEventsTask.create() //
                            .setRootPath(PUBLIC_ROOT_PATH) //
                            .setBeforeRoot(Optional.of(metadataTree)) //
                            .setAfterRoot(proposedSubtree) //
                            .setModificationRoot(modification) //
                            .setListenerRoot(listenerTree);

                    return null;
                }
            });
        }

        @Override
        public ListenableFuture<Void> abort() {
            storeSnapshot = null;
            proposedSubtree = null;
            return Futures.<Void> immediateFuture(null);
        }

        @Override
        public ListenableFuture<Void> commit() {
            if(modification.getModificationType() == ModificationType.UNMODIFIED) {
                return Futures.immediateFuture(null);
            }

            checkState(proposedSubtree != null,"Proposed subtree must be computed");
            checkState(storeSnapshot != null,"Proposed subtree must be computed");
            // return ImmediateFuture<>;
            InMemoryDOMDataStore.this.commit(storeSnapshot, proposedSubtree.get(),listenerResolver);
            return Futures.<Void> immediateFuture(null);
        }

    }

    private static final class AlwaysFailOperation implements ModificationApplyOperation {

        @Override
        public Optional<StoreMetadataNode> apply(final NodeModification modification,
                final Optional<StoreMetadataNode> storeMeta, final UnsignedLong subtreeVersion) {
            throw new IllegalStateException("Schema Context is not available.");
        }

        @Override
        public boolean isApplicable(final NodeModification modification, final Optional<StoreMetadataNode> storeMetadata) {
            throw new IllegalStateException("Schema Context is not available.");
        }

        @Override
        public Optional<ModificationApplyOperation> getChild(final PathArgument child) {
            throw new IllegalStateException("Schema Context is not available.");
        }

        @Override
        public void verifyStructure(final NodeModification modification) throws IllegalArgumentException {
            throw new IllegalStateException("Schema Context is not available.");
        }

    }
}