/*
 * 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.common.typeutils.base;

import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.typeutils.CompatibilityResult;
import org.apache.flink.api.common.typeutils.CompatibilityUtil;
import org.apache.flink.api.common.typeutils.TypeDeserializerAdapter;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.api.common.typeutils.TypeSerializerConfigSnapshot;
import org.apache.flink.api.common.typeutils.UnloadableDummyTypeSerializer;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.util.Preconditions;

import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.HashMap;

/**
 * A serializer for {@link Map}. The serializer relies on a key serializer and a value serializer
 * for the serialization of the map's key-value pairs.
 *
 * <p>The serialization format for the map is as follows: four bytes for the length of the map,
 * followed by the serialized representation of each key-value pair. To allow null values, each value
 * is prefixed by a null marker.
 *
 * @param <K> The type of the keys in the map.
 * @param <V> The type of the values in the map.
 */
@Internal
public final class MapSerializer<K, V> extends TypeSerializer<Map<K, V>> {

	private static final long serialVersionUID = -6885593032367050078L;
	
	/** The serializer for the keys in the map */
	private final TypeSerializer<K> keySerializer;

	/** The serializer for the values in the map */
	private final TypeSerializer<V> valueSerializer;

	/**
	 * Creates a map serializer that uses the given serializers to serialize the key-value pairs in the map.
	 *
	 * @param keySerializer The serializer for the keys in the map
	 * @param valueSerializer The serializer for the values in the map
	 */
	public MapSerializer(TypeSerializer<K> keySerializer, TypeSerializer<V> valueSerializer) {
		this.keySerializer = Preconditions.checkNotNull(keySerializer, "The key serializer cannot be null");
		this.valueSerializer = Preconditions.checkNotNull(valueSerializer, "The value serializer cannot be null.");
	}

	// ------------------------------------------------------------------------
	//  MapSerializer specific properties
	// ------------------------------------------------------------------------

	public TypeSerializer<K> getKeySerializer() {
		return keySerializer;
	}

	public TypeSerializer<V> getValueSerializer() {
		return valueSerializer;
	}

	// ------------------------------------------------------------------------
	//  Type Serializer implementation
	// ------------------------------------------------------------------------

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

	@Override
	public TypeSerializer<Map<K, V>> duplicate() {
		TypeSerializer<K> duplicateKeySerializer = keySerializer.duplicate();
		TypeSerializer<V> duplicateValueSerializer = valueSerializer.duplicate();

		return (duplicateKeySerializer == keySerializer) && (duplicateValueSerializer == valueSerializer)
				? this
				: new MapSerializer<>(duplicateKeySerializer, duplicateValueSerializer);
	}

	@Override
	public Map<K, V> createInstance() {
		return new HashMap<>();
	}

	@Override
	public Map<K, V> copy(Map<K, V> from) {
		Map<K, V> newMap = new HashMap<>(from.size());

		for (Map.Entry<K, V> entry : from.entrySet()) {
			K newKey = keySerializer.copy(entry.getKey());
			V newValue = entry.getValue() == null ? null : valueSerializer.copy(entry.getValue());

			newMap.put(newKey, newValue);
		}

		return newMap;
	}

	@Override
	public Map<K, V> copy(Map<K, V> from, Map<K, V> reuse) {
		return copy(from);
	}

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

	@Override
	public void serialize(Map<K, V> map, DataOutputView target) throws IOException {
		final int size = map.size();
		target.writeInt(size);

		for (Map.Entry<K, V> entry : map.entrySet()) {
			keySerializer.serialize(entry.getKey(), target);

			if (entry.getValue() == null) {
				target.writeBoolean(true);
			} else {
				target.writeBoolean(false);
				valueSerializer.serialize(entry.getValue(), target);
			}
		}
	}

	@Override
	public Map<K, V> deserialize(DataInputView source) throws IOException {
		final int size = source.readInt();

		final Map<K, V> map = new HashMap<>(size);
		for (int i = 0; i < size; ++i) {
			K key = keySerializer.deserialize(source);

			boolean isNull = source.readBoolean();
			V value = isNull ? null : valueSerializer.deserialize(source);

			map.put(key, value);
		}

		return map;
	}

	@Override
	public Map<K, V> deserialize(Map<K, V> reuse, DataInputView source) throws IOException {
		return deserialize(source);
	}

	@Override
	public void copy(DataInputView source, DataOutputView target) throws IOException {
		final int size = source.readInt();
		target.writeInt(size);

		for (int i = 0; i < size; ++i) {
			keySerializer.copy(source, target);
			
			boolean isNull = source.readBoolean();
			target.writeBoolean(isNull);
			
			if (!isNull) {
				valueSerializer.copy(source, target);
			}
		}
	}

	@Override
	public boolean equals(Object obj) {
		return obj == this ||
				(obj != null && obj.getClass() == getClass() &&
						keySerializer.equals(((MapSerializer<?, ?>) obj).getKeySerializer()) &&
						valueSerializer.equals(((MapSerializer<?, ?>) obj).getValueSerializer()));
	}

	@Override
	public boolean canEqual(Object obj) {
		return (obj != null && obj.getClass() == getClass());
	}

	@Override
	public int hashCode() {
		return keySerializer.hashCode() * 31 + valueSerializer.hashCode();
	}

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

	@Override
	public MapSerializerConfigSnapshot snapshotConfiguration() {
		return new MapSerializerConfigSnapshot<>(keySerializer, valueSerializer);
	}

	@Override
	public CompatibilityResult<Map<K, V>> ensureCompatibility(TypeSerializerConfigSnapshot configSnapshot) {
		if (configSnapshot instanceof MapSerializerConfigSnapshot) {
			List<Tuple2<TypeSerializer<?>, TypeSerializerConfigSnapshot>> previousKvSerializersAndConfigs =
				((MapSerializerConfigSnapshot) configSnapshot).getNestedSerializersAndConfigs();

			CompatibilityResult<K> keyCompatResult = CompatibilityUtil.resolveCompatibilityResult(
					previousKvSerializersAndConfigs.get(0).f0,
					UnloadableDummyTypeSerializer.class,
					previousKvSerializersAndConfigs.get(0).f1,
					keySerializer);

			CompatibilityResult<V> valueCompatResult = CompatibilityUtil.resolveCompatibilityResult(
					previousKvSerializersAndConfigs.get(1).f0,
					UnloadableDummyTypeSerializer.class,
					previousKvSerializersAndConfigs.get(1).f1,
					valueSerializer);

			if (!keyCompatResult.isRequiresMigration() && !valueCompatResult.isRequiresMigration()) {
				return CompatibilityResult.compatible();
			} else if (keyCompatResult.getConvertDeserializer() != null && valueCompatResult.getConvertDeserializer() != null) {
				return CompatibilityResult.requiresMigration(
					new MapSerializer<>(
						new TypeDeserializerAdapter<>(keyCompatResult.getConvertDeserializer()),
						new TypeDeserializerAdapter<>(valueCompatResult.getConvertDeserializer())));
			}
		}

		return CompatibilityResult.requiresMigration();
	}
}