/*
 * 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.api.java.typeutils.runtime;

import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.typeutils.CompatibilityResult;
import org.apache.flink.api.common.typeutils.GenericTypeSerializerConfigSnapshot;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.api.common.typeutils.TypeSerializerConfigSnapshot;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.util.InstantiationUtil;

import com.esotericsoftware.kryo.Kryo;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Writable;
import org.objenesis.strategy.StdInstantiatorStrategy;

import java.io.IOException;

/**
 * A {@link TypeSerializer} for {@link Writable}.
 * @param <T>
 */
@Internal
public final class WritableSerializer<T extends Writable> extends TypeSerializer<T> {

	private static final long serialVersionUID = 1L;

	private final Class<T> typeClass;

	private transient Kryo kryo;

	private transient T copyInstance;

	public WritableSerializer(Class<T> typeClass) {
		this.typeClass = typeClass;
	}

	@SuppressWarnings("unchecked")
	@Override
	public T createInstance() {
		if (typeClass == NullWritable.class) {
			return (T) NullWritable.get();
		}
		return InstantiationUtil.instantiate(typeClass);
	}

	@Override
	public T copy(T from) {
		checkKryoInitialized();

		return KryoUtils.copy(from, kryo, this);
	}

	@Override
	public T copy(T from, T reuse) {
		checkKryoInitialized();

		return KryoUtils.copy(from, reuse, kryo, this);
	}

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

	@Override
	public void serialize(T record, DataOutputView target) throws IOException {
		record.write(target);
	}

	@Override
	public T deserialize(DataInputView source) throws IOException {
		return deserialize(createInstance(), source);
	}

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

	@Override
	public void copy(DataInputView source, DataOutputView target) throws IOException {
		ensureInstanceInstantiated();
		copyInstance.readFields(source);
		copyInstance.write(target);
	}

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

	@Override
	public WritableSerializer<T> duplicate() {
		return new WritableSerializer<T>(typeClass);
	}

	// --------------------------------------------------------------------------------------------

	private void ensureInstanceInstantiated() {
		if (copyInstance == null) {
			copyInstance = createInstance();
		}
	}

	private void checkKryoInitialized() {
		if (this.kryo == null) {
			this.kryo = new Kryo();

			Kryo.DefaultInstantiatorStrategy instantiatorStrategy = new Kryo.DefaultInstantiatorStrategy();
			instantiatorStrategy.setFallbackInstantiatorStrategy(new StdInstantiatorStrategy());
			kryo.setInstantiatorStrategy(instantiatorStrategy);

			this.kryo.setAsmEnabled(true);
			this.kryo.register(typeClass);
		}
	}
	// --------------------------------------------------------------------------------------------

	@Override
	public int hashCode() {
		return this.typeClass.hashCode();
	}

	@Override
	public boolean equals(Object obj) {
		if (obj instanceof WritableSerializer) {
			WritableSerializer<?> other = (WritableSerializer<?>) obj;

			return other.canEqual(this) && typeClass == other.typeClass;
		} else {
			return false;
		}
	}

	@Override
	public boolean canEqual(Object obj) {
		return obj instanceof WritableSerializer;
	}

	// --------------------------------------------------------------------------------------------
	// Serializer configuration snapshotting & compatibility
	// --------------------------------------------------------------------------------------------

	@Override
	public WritableSerializerConfigSnapshot<T> snapshotConfiguration() {
		return new WritableSerializerConfigSnapshot<>(typeClass);
	}

	@Override
	public CompatibilityResult<T> ensureCompatibility(TypeSerializerConfigSnapshot configSnapshot) {
		if (configSnapshot instanceof WritableSerializerConfigSnapshot
				&& typeClass.equals(((WritableSerializerConfigSnapshot) configSnapshot).getTypeClass())) {

			return CompatibilityResult.compatible();
		} else {
			return CompatibilityResult.requiresMigration();
		}
	}

	/**
	 * The config snapshot for this serializer.
	 * @param <T>
	 */
	public static final class WritableSerializerConfigSnapshot<T extends Writable>
			extends GenericTypeSerializerConfigSnapshot<T> {

		private static final int VERSION = 1;

		/** This empty nullary constructor is required for deserializing the configuration. */
		public WritableSerializerConfigSnapshot() {}

		public WritableSerializerConfigSnapshot(Class<T> writableTypeClass) {
			super(writableTypeClass);
		}

		@Override
		public int getVersion() {
			return VERSION;
		}
	}
}