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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.sharedbuffer;

import org.apache.flink.annotation.VisibleForTesting;
import org.apache.flink.api.common.typeutils.CompositeTypeSerializerUtil;
import org.apache.flink.api.common.typeutils.LegacySerializerSnapshotTransformer;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.api.common.typeutils.TypeSerializerSnapshot;
import org.apache.flink.api.common.typeutils.base.IntSerializer;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;

import java.io.IOException;
import java.util.Objects;

/**
 * Implements locking logic for incoming event and {@link SharedBufferNode} using a lock reference
 * counter.
 */
public final class Lockable {

    private int refCounter;

    private final T element;

    public Lockable(T element, int refCounter) {
        this.refCounter = refCounter;
        this.element = element;
    }

    public void lock() {
        refCounter += 1;
    }

    /**
     * Releases lock on this object. If no more locks are acquired on it, this method will return
     * true.
     *
     * @return true if no more locks are acquired
     */
    boolean release() {
        if (refCounter <= 0) {
            return true;
        }

        refCounter -= 1;
        return refCounter == 0;
    }

    public T getElement() {
        return element;
    }

    int getRefCounter() {
        return refCounter;
    }

    @Override
    public String toString() {
        return "Lock{" + "refCounter=" + refCounter + '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        Lockable lockable = (Lockable) o;
        return refCounter == lockable.refCounter && Objects.equals(element, lockable.element);
    }

    @Override
    public int hashCode() {
        return Objects.hash(refCounter, element);
    }

    /** Serializer for {@link Lockable}. */
    public static class LockableTypeSerializer extends TypeSerializer>
            implements LegacySerializerSnapshotTransformer> {

        private static final long serialVersionUID = 3298801058463337340L;
        private final TypeSerializer elementSerializer;

        public LockableTypeSerializer(TypeSerializer elementSerializer) {
            this.elementSerializer = elementSerializer;
        }

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

        @Override
        public LockableTypeSerializer duplicate() {
            TypeSerializer elementSerializerCopy = elementSerializer.duplicate();
            return elementSerializerCopy == elementSerializer
                    ? this
                    : new LockableTypeSerializer<>(elementSerializerCopy);
        }

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

        @Override
        public Lockable copy(Lockable from) {
            return new Lockable<>(elementSerializer.copy(from.element), from.refCounter);
        }

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

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

        @Override
        public void serialize(Lockable record, DataOutputView target) throws IOException {
            IntSerializer.INSTANCE.serialize(record.refCounter, target);
            elementSerializer.serialize(record.element, target);
        }

        @Override
        public Lockable deserialize(DataInputView source) throws IOException {
            int refCount = IntSerializer.INSTANCE.deserialize(source);
            E record = elementSerializer.deserialize(source);
            return new Lockable<>(record, refCount);
        }

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

        @Override
        public void copy(DataInputView source, DataOutputView target) throws IOException {
            IntSerializer.INSTANCE.copy(source, target); // refCounter

            E element = elementSerializer.deserialize(source);
            elementSerializer.serialize(element, target);
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            LockableTypeSerializer that = (LockableTypeSerializer) o;
            return Objects.equals(elementSerializer, that.elementSerializer);
        }

        @Override
        public int hashCode() {
            return Objects.hash(elementSerializer);
        }

        @Override
        public TypeSerializerSnapshot> snapshotConfiguration() {
            return new LockableTypeSerializerSnapshot<>(this);
        }

        @VisibleForTesting
        TypeSerializer getElementSerializer() {
            return elementSerializer;
        }

        @Override
        @SuppressWarnings("unchecked")
        public  TypeSerializerSnapshot> transformLegacySerializerSnapshot(
                TypeSerializerSnapshot legacySnapshot) {
            if (legacySnapshot instanceof LockableTypeSerializerSnapshot) {
                return (TypeSerializerSnapshot>) legacySnapshot;
            }

            LockableTypeSerializerSnapshot lockableSnapshot =
                    new LockableTypeSerializerSnapshot<>();
            CompositeTypeSerializerUtil.setNestedSerializersSnapshots(
                    lockableSnapshot, legacySnapshot);
            return lockableSnapshot;
        }
    }
}