/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.tinkerpop.gremlin.structure.io.gryo;

import org.apache.tinkerpop.gremlin.process.computer.GraphFilter;
import org.apache.tinkerpop.gremlin.structure.Direction;
import org.apache.tinkerpop.gremlin.structure.Edge;
import org.apache.tinkerpop.gremlin.structure.Graph;
import org.apache.tinkerpop.gremlin.structure.Property;
import org.apache.tinkerpop.gremlin.structure.T;
import org.apache.tinkerpop.gremlin.structure.Vertex;
import org.apache.tinkerpop.gremlin.structure.VertexProperty;
import org.apache.tinkerpop.gremlin.structure.io.GraphReader;
import org.apache.tinkerpop.gremlin.structure.io.GraphWriter;
import org.apache.tinkerpop.gremlin.structure.io.Mapper;
import org.apache.tinkerpop.gremlin.structure.util.Attachable;
import org.apache.tinkerpop.gremlin.structure.util.Host;
import org.apache.tinkerpop.gremlin.structure.util.detached.DetachedEdge;
import org.apache.tinkerpop.gremlin.structure.util.detached.DetachedProperty;
import org.apache.tinkerpop.gremlin.structure.util.detached.DetachedVertexProperty;
import org.apache.tinkerpop.gremlin.structure.util.star.StarGraph;
import org.apache.tinkerpop.gremlin.structure.util.star.StarGraphGryoSerializer;
import org.apache.tinkerpop.gremlin.util.iterator.IteratorUtils;
import org.apache.tinkerpop.shaded.kryo.Kryo;
import org.apache.tinkerpop.shaded.kryo.io.Input;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.Function;

/**
 * The {@link GraphReader} for the Gremlin Structure serialization format based on Kryo.  The format is meant to be
 * non-lossy in terms of Gremlin Structure to Gremlin Structure migrations (assuming both structure implementations
 * support the same graph features).
 * <p/>
 * This implementation is not thread-safe.  Have one {@code GryoReader} instance per thread.
 *
 * @author Stephen Mallette (http://stephen.genoprime.com)
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public final class GryoReader implements GraphReader {
    private final Kryo kryo;
    private final Map<GraphFilter, StarGraphGryoSerializer> graphFilterCache = new HashMap<>();

    private final long batchSize;

    private GryoReader(final long batchSize, final Mapper<Kryo> gryoMapper) {
        this.kryo = gryoMapper.createMapper();
        this.batchSize = batchSize;
    }

    /**
     * Read data into a {@link Graph} from output generated by any of the {@link GryoWriter} {@code writeVertex} or
     * {@code writeVertices} methods or by {@link GryoWriter#writeGraph(OutputStream, Graph)}.
     *
     * @param inputStream    a stream containing an entire graph of vertices and edges as defined by the accompanying
     *                       {@link GraphWriter#writeGraph(OutputStream, Graph)}.
     * @param graphToWriteTo the graph to write to when reading from the stream.
     * @throws IOException
     */
    @Override
    public void readGraph(final InputStream inputStream, final Graph graphToWriteTo) throws IOException {
        // dual pass - create all vertices and store to cache the ids.  then create edges.  as long as we don't
        // have vertex labels in the output we can't do this single pass
        final Map<StarGraph.StarVertex, Vertex> cache = new HashMap<>();
        final AtomicLong counter = new AtomicLong(0);

        final Graph.Features.EdgeFeatures edgeFeatures = graphToWriteTo.features().edge();
        final boolean supportsTx = graphToWriteTo.features().graph().supportsTransactions();

        IteratorUtils.iterate(new VertexInputIterator(new Input(inputStream), attachable -> {
            final Vertex v = cache.put((StarGraph.StarVertex) attachable.get(), attachable.attach(Attachable.Method.create(graphToWriteTo)));
            if (supportsTx && counter.incrementAndGet() % batchSize == 0)
                graphToWriteTo.tx().commit();
            return v;
        }, null, null));
        cache.entrySet().forEach(kv -> kv.getKey().edges(Direction.IN).forEachRemaining(e -> {
            // can't use a standard Attachable attach method here because we have to use the cache for those
            // graphs that don't support userSuppliedIds on edges. note that outVertex/inVertex methods return
            // StarAdjacentVertex whose equality should match StarVertex.
            final Vertex cachedOutV = cache.get(e.outVertex());
            final Vertex cachedInV = cache.get(e.inVertex());

            if (null == cachedOutV) throw new IllegalStateException(String.format("Could not find outV with id [%s] to create edge with id [%s]", e.outVertex().id(), e.id()));
            if (null == cachedInV) throw new IllegalStateException(String.format("Could not find inV with id [%s] to create edge with id [%s]", e.inVertex().id(), e.id()));

            final Edge newEdge = edgeFeatures.willAllowId(e.id()) ? cachedOutV.addEdge(e.label(), cachedInV, T.id, e.id()) : cachedOutV.addEdge(e.label(), cachedInV);
            e.properties().forEachRemaining(p -> newEdge.property(p.key(), p.value()));
            if (supportsTx && counter.incrementAndGet() % batchSize == 0)
                graphToWriteTo.tx().commit();
        }));

        if (supportsTx) graphToWriteTo.tx().commit();
    }

    @Override
    public Optional<Vertex> readVertex(final InputStream inputStream, final GraphFilter graphFilter) throws IOException {
        StarGraphGryoSerializer serializer = this.graphFilterCache.get(graphFilter);
        if (null == serializer) {
            serializer = StarGraphGryoSerializer.withGraphFilter(graphFilter);
            this.graphFilterCache.put(graphFilter, serializer);
        }
        final Input input = new Input(inputStream);
        this.readHeader(input);
        final StarGraph starGraph = this.kryo.readObject(input, StarGraph.class, serializer);
        // read the terminator
        this.kryo.readClassAndObject(input);
        return Optional.ofNullable(starGraph == null ? null : starGraph.getStarVertex());
    }

    /**
     * Read {@link Vertex} objects from output generated by any of the {@link GryoWriter} {@code writeVertex} or
     * {@code writeVertices} methods or by {@link GryoWriter#writeGraph(OutputStream, Graph)}.
     *
     * @param inputStream                a stream containing at least one {@link Vertex} as defined by the accompanying
     *                                   {@link GraphWriter#writeVertices(OutputStream, Iterator, Direction)} or
     *                                   {@link GraphWriter#writeVertices(OutputStream, Iterator)} methods.
     * @param vertexAttachMethod         a function that creates re-attaches a {@link Vertex} to a {@link Host} object.
     * @param edgeAttachMethod           a function that creates re-attaches a {@link Edge} to a {@link Host} object.
     * @param attachEdgesOfThisDirection only edges of this direction are passed to the {@code edgeMaker}.
     */
    @Override
    public Iterator<Vertex> readVertices(final InputStream inputStream,
                                         final Function<Attachable<Vertex>, Vertex> vertexAttachMethod,
                                         final Function<Attachable<Edge>, Edge> edgeAttachMethod,
                                         final Direction attachEdgesOfThisDirection) throws IOException {
        return new VertexInputIterator(new Input(inputStream), vertexAttachMethod, attachEdgesOfThisDirection, edgeAttachMethod);
    }

    /**
     * Read a {@link Vertex}  from output generated by any of the {@link GryoWriter} {@code writeVertex} or
     * {@code writeVertices} methods or by {@link GryoWriter#writeGraph(OutputStream, Graph)}.
     *
     * @param inputStream        a stream containing at least a single vertex as defined by the accompanying
     *                           {@link GraphWriter#writeVertex(OutputStream, Vertex)}.
     * @param vertexAttachMethod a function that creates re-attaches a {@link Vertex} to a {@link Host} object.
     */
    @Override
    public Vertex readVertex(final InputStream inputStream, final Function<Attachable<Vertex>, Vertex> vertexAttachMethod) throws IOException {
        return readVertex(inputStream, vertexAttachMethod, null, null);
    }

    /**
     * Read a {@link Vertex} from output generated by any of the {@link GryoWriter} {@code writeVertex} or
     * {@code writeVertices} methods or by {@link GryoWriter#writeGraph(OutputStream, Graph)}.
     *
     * @param inputStream                a stream containing at least one {@link Vertex} as defined by the accompanying
     *                                   {@link GraphWriter#writeVertices(OutputStream, Iterator, Direction)} method.
     * @param vertexAttachMethod         a function that creates re-attaches a {@link Vertex} to a {@link Host} object.
     * @param edgeAttachMethod           a function that creates re-attaches a {@link Edge} to a {@link Host} object.
     * @param attachEdgesOfThisDirection only edges of this direction are passed to the {@code edgeMaker}.
     */
    @Override
    public Vertex readVertex(final InputStream inputStream,
                             final Function<Attachable<Vertex>, Vertex> vertexAttachMethod,
                             final Function<Attachable<Edge>, Edge> edgeAttachMethod,
                             final Direction attachEdgesOfThisDirection) throws IOException {
        final Input input = new Input(inputStream);
        return readVertexInternal(vertexAttachMethod, edgeAttachMethod, attachEdgesOfThisDirection, input);
    }

    /**
     * Read an {@link Edge} from output generated by {@link GryoWriter#writeEdge(OutputStream, Edge)} or via
     * an {@link Edge} passed to {@link GryoWriter#writeObject(OutputStream, Object)}.
     *
     * @param inputStream      a stream containing at least one {@link Edge} as defined by the accompanying
     *                         {@link GraphWriter#writeEdge(OutputStream, Edge)} method.
     * @param edgeAttachMethod a function that creates re-attaches a {@link Edge} to a {@link Host} object.
     */
    @Override
    public Edge readEdge(final InputStream inputStream, final Function<Attachable<Edge>, Edge> edgeAttachMethod) throws IOException {
        final Input input = new Input(inputStream);
        readHeader(input);
        final Attachable<Edge> attachable = kryo.readObject(input, DetachedEdge.class);
        return edgeAttachMethod.apply(attachable);
    }

    /**
     * Read a {@link VertexProperty} from output generated by
     * {@link GryoWriter#writeVertexProperty(OutputStream, VertexProperty)} or via an {@link VertexProperty} passed
     * to {@link GryoWriter#writeObject(OutputStream, Object)}.
     *
     * @param inputStream                a stream containing at least one {@link VertexProperty} as written by the accompanying
     *                                   {@link GraphWriter#writeVertexProperty(OutputStream, VertexProperty)} method.
     * @param vertexPropertyAttachMethod a function that creates re-attaches a {@link VertexProperty} to a
     *                                   {@link Host} object.
     */
    @Override
    public VertexProperty readVertexProperty(final InputStream inputStream,
                                             final Function<Attachable<VertexProperty>, VertexProperty> vertexPropertyAttachMethod) throws IOException {
        final Input input = new Input(inputStream);
        readHeader(input);
        final Attachable<VertexProperty> attachable = kryo.readObject(input, DetachedVertexProperty.class);
        return vertexPropertyAttachMethod.apply(attachable);
    }

    /**
     * Read a {@link Property} from output generated by  {@link GryoWriter#writeProperty(OutputStream, Property)} or
     * via an {@link Property} passed to {@link GryoWriter#writeObject(OutputStream, Object)}.
     *
     * @param inputStream          a stream containing at least one {@link Property} as written by the accompanying
     *                             {@link GraphWriter#writeProperty(OutputStream, Property)} method.
     * @param propertyAttachMethod a function that creates re-attaches a {@link Property} to a {@link Host} object.
     */
    @Override
    public Property readProperty(final InputStream inputStream,
                                 final Function<Attachable<Property>, Property> propertyAttachMethod) throws IOException {
        final Input input = new Input(inputStream);
        readHeader(input);
        final Attachable<Property> attachable = kryo.readObject(input, DetachedProperty.class);
        return propertyAttachMethod.apply(attachable);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public <C> C readObject(final InputStream inputStream, final Class<? extends C> clazz) throws IOException {
        return clazz.cast(this.kryo.readClassAndObject(new Input(inputStream)));
    }

    private Vertex readVertexInternal(final Function<Attachable<Vertex>, Vertex> vertexMaker,
                                      final Function<Attachable<Edge>, Edge> edgeMaker,
                                      final Direction d,
                                      final Input input) throws IOException {
        readHeader(input);
        final StarGraph starGraph = kryo.readObject(input, StarGraph.class);

        // read the terminator
        kryo.readClassAndObject(input);

        final Vertex v = vertexMaker.apply(starGraph.getStarVertex());
        if (edgeMaker != null)
            starGraph.getStarVertex().edges(d).forEachRemaining(e -> edgeMaker.apply((Attachable<Edge>) e));
        return v;
    }

    private void readHeader(final Input input) throws IOException {
        if (!Arrays.equals(GryoMapper.GIO, input.readBytes(3)))
            throw new IOException("Invalid format - first three bytes of header do not match expected value");

        // skip the next 13 bytes - for future use
        input.readBytes(13);
    }

    public static Builder build() {
        return new Builder();
    }

    public final static class Builder implements ReaderBuilder<GryoReader> {

        private long batchSize = 10000;
        /**
         * Always use the most recent gryo version by default
         */
        private Mapper<Kryo> gryoMapper = GryoMapper.build().create();

        private Builder() {
        }

        /**
         * Number of mutations to perform before a commit is executed when using
         * {@link GryoReader#readGraph(InputStream, Graph)}.
         */
        public Builder batchSize(final long batchSize) {
            this.batchSize = batchSize;
            return this;
        }

        /**
         * Supply a mapper {@link GryoMapper} instance to use as the serializer for the {@code KryoWriter}.
         */
        public Builder mapper(final Mapper<Kryo> gryoMapper) {
            this.gryoMapper = gryoMapper;
            return this;
        }

        public GryoReader create() {
            return new GryoReader(batchSize, this.gryoMapper);
        }

    }

    private class VertexInputIterator implements Iterator<Vertex> {
        private final Input input;
        private final Function<Attachable<Vertex>, Vertex> vertexMaker;
        private final Direction d;
        private final Function<Attachable<Edge>, Edge> edgeMaker;

        public VertexInputIterator(final Input input,
                                   final Function<Attachable<Vertex>, Vertex> vertexMaker,
                                   final Direction d,
                                   final Function<Attachable<Edge>, Edge> edgeMaker) {
            this.input = input;
            this.d = d;
            this.edgeMaker = edgeMaker;
            this.vertexMaker = vertexMaker;
        }

        @Override
        public boolean hasNext() {
            return !input.eof();
        }

        @Override
        public Vertex next() {
            try {
                return readVertexInternal(vertexMaker, edgeMaker, d, input);
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }
        }
    }
}
