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/*
 * 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.flink.cep.nfa;

import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.api.common.typeutils.TypeSerializerSnapshot;
import org.apache.flink.api.common.typeutils.base.TypeSerializerSingleton;
import org.apache.flink.cep.nfa.sharedbuffer.EventId;
import org.apache.flink.cep.nfa.sharedbuffer.NodeId;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataInputViewStreamWrapper;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.core.memory.DataOutputViewStreamWrapper;
import org.apache.flink.types.StringValue;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.util.PriorityQueue;
import java.util.Queue;

import static org.apache.flink.util.Preconditions.checkNotNull;

/** A {@link TypeSerializer} for {@link NFAState}. */
public class NFAStateSerializer extends TypeSerializerSingleton {

    private static final long serialVersionUID = 2098282423980597010L;

    /**
     * NOTE: this field should actually be final. The reason that it isn't final is due to backward
     * compatible deserialization paths. See {@link #readObject(ObjectInputStream)}.
     */
    private TypeSerializer versionSerializer;

    private TypeSerializer nodeIdSerializer;
    private TypeSerializer eventIdSerializer;

    private final boolean supportsPreviousTimestamp;

    public NFAStateSerializer() {
        this(
                DeweyNumber.DeweyNumberSerializer.INSTANCE,
                new NodeId.NodeIdSerializer(),
                EventId.EventIdSerializer.INSTANCE,
                true);
    }

    NFAStateSerializer(
            final TypeSerializer versionSerializer,
            final TypeSerializer nodeIdSerializer,
            final TypeSerializer eventIdSerializer,
            final boolean supportsPreviousTimestamp) {
        this.versionSerializer = checkNotNull(versionSerializer);
        this.nodeIdSerializer = checkNotNull(nodeIdSerializer);
        this.eventIdSerializer = checkNotNull(eventIdSerializer);
        this.supportsPreviousTimestamp = supportsPreviousTimestamp;
    }

    public boolean isSupportsPreviousTimestamp() {
        return supportsPreviousTimestamp;
    }

    @Override
    public boolean isImmutableType() {
        return false;
    }

    @Override
    public NFAState createInstance() {
        return null;
    }

    @Override
    public NFAState copy(NFAState from) {
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            serialize(from, new DataOutputViewStreamWrapper(baos));
            baos.close();

            byte[] data = baos.toByteArray();

            ByteArrayInputStream bais = new ByteArrayInputStream(data);
            NFAState copy = deserialize(new DataInputViewStreamWrapper(bais));
            bais.close();
            return copy;
        } catch (IOException e) {
            throw new RuntimeException("Could not copy NFA.", e);
        }
    }

    @Override
    public NFAState copy(NFAState from, NFAState reuse) {
        return copy(from);
    }

    @Override
    public int getLength() {
        return -1;
    }

    @Override
    public void serialize(NFAState record, DataOutputView target) throws IOException {
        serializeComputationStates(record.getPartialMatches(), target);
        serializeComputationStates(record.getCompletedMatches(), target);
    }

    @Override
    public NFAState deserialize(DataInputView source) throws IOException {
        PriorityQueue partialMatches = deserializeComputationStates(source);
        PriorityQueue completedMatches = deserializeComputationStates(source);
        return new NFAState(partialMatches, completedMatches);
    }

    @Override
    public NFAState deserialize(NFAState reuse, DataInputView source) throws IOException {
        return deserialize(source);
    }

    @Override
    public void copy(DataInputView source, DataOutputView target) throws IOException {
        copyStates(source, target); // copy partial matches
        copyStates(source, target); // copy completed matches
    }

    private void copyStates(DataInputView source, DataOutputView target) throws IOException {
        int computationStateNo = source.readInt();
        target.writeInt(computationStateNo);

        for (int i = 0; i < computationStateNo; i++) {
            copySingleComputationState(source, target);
        }
    }

    @Override
    public TypeSerializerSnapshot snapshotConfiguration() {
        return new NFAStateSerializerSnapshot(this);
    }

    /*
    Getters for internal serializers to use in NFAStateSerializerSnapshot.
    */

    TypeSerializer getVersionSerializer() {
        return versionSerializer;
    }

    TypeSerializer getNodeIdSerializer() {
        return nodeIdSerializer;
    }

    TypeSerializer getEventIdSerializer() {
        return eventIdSerializer;
    }

    /*
    De/serialization methods
    */

    private void serializeComputationStates(Queue states, DataOutputView target)
            throws IOException {
        target.writeInt(states.size());
        for (ComputationState computationState : states) {
            serializeSingleComputationState(computationState, target);
        }
    }

    private PriorityQueue deserializeComputationStates(DataInputView source)
            throws IOException {
        PriorityQueue computationStates =
                new PriorityQueue<>(NFAState.COMPUTATION_STATE_COMPARATOR);

        int computationStateNo = source.readInt();
        for (int i = 0; i < computationStateNo; i++) {
            final ComputationState computationState = deserializeSingleComputationState(source);
            computationStates.add(computationState);
        }
        return computationStates;
    }

    private void serializeSingleComputationState(
            ComputationState computationState, DataOutputView target) throws IOException {

        StringValue.writeString(computationState.getCurrentStateName(), target);
        nodeIdSerializer.serialize(computationState.getPreviousBufferEntry(), target);
        versionSerializer.serialize(computationState.getVersion(), target);
        target.writeLong(computationState.getStartTimestamp());
        if (supportsPreviousTimestamp) {
            target.writeLong(computationState.getPreviousTimestamp());
        }
        serializeStartEvent(computationState.getStartEventID(), target);
    }

    private ComputationState deserializeSingleComputationState(DataInputView source)
            throws IOException {
        String stateName = StringValue.readString(source);
        NodeId prevState = nodeIdSerializer.deserialize(source);
        DeweyNumber version = versionSerializer.deserialize(source);
        long startTimestamp = source.readLong();
        long previousTimestamp = -1L;
        if (supportsPreviousTimestamp) {
            previousTimestamp = source.readLong();
        }

        EventId startEventId = deserializeStartEvent(source);

        return ComputationState.createState(
                stateName, prevState, version, startTimestamp, previousTimestamp, startEventId);
    }

    private void copySingleComputationState(DataInputView source, DataOutputView target)
            throws IOException {
        StringValue.copyString(source, target);
        NodeId prevState = nodeIdSerializer.deserialize(source);
        nodeIdSerializer.serialize(prevState, target);
        DeweyNumber version = versionSerializer.deserialize(source);
        versionSerializer.serialize(version, target);
        long startTimestamp = source.readLong();
        target.writeLong(startTimestamp);
        if (supportsPreviousTimestamp) {
            long previousTimestamp = source.readLong();
            target.writeLong(previousTimestamp);
        }

        copyStartEvent(source, target);
    }

    private void serializeStartEvent(EventId startEventID, DataOutputView target)
            throws IOException {
        if (startEventID != null) {
            target.writeByte(1);
            eventIdSerializer.serialize(startEventID, target);
        } else {
            target.writeByte(0);
        }
    }

    private EventId deserializeStartEvent(DataInputView source) throws IOException {
        byte isNull = source.readByte();
        EventId startEventId = null;
        if (isNull == 1) {
            startEventId = eventIdSerializer.deserialize(source);
        }
        return startEventId;
    }

    private void copyStartEvent(DataInputView source, DataOutputView target) throws IOException {
        byte isNull = source.readByte();
        target.writeByte(isNull);

        if (isNull == 1) {
            EventId startEventId = eventIdSerializer.deserialize(source);
            eventIdSerializer.serialize(startEventId, target);
        }
    }

    /*
     * Backwards compatible deserializing of NFAStateSerializer.
     */
    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();

        // the nested serializer will be null if this was read from a savepoint taken with versions
        // lower than Flink 1.7; in this case, we explicitly create instance for the nested
        // serializer.
        if (versionSerializer == null || nodeIdSerializer == null || eventIdSerializer == null) {
            this.versionSerializer = DeweyNumber.DeweyNumberSerializer.INSTANCE;
            this.eventIdSerializer = EventId.EventIdSerializer.INSTANCE;
            this.nodeIdSerializer = new NodeId.NodeIdSerializer();
        }
    }
}