/*
 * 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.contrib.streaming.state;

import org.apache.flink.api.common.functions.AggregateFunction;
import org.apache.flink.api.common.state.AggregatingState;
import org.apache.flink.api.common.state.AggregatingStateDescriptor;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.core.memory.ByteArrayInputStreamWithPos;
import org.apache.flink.core.memory.DataInputViewStreamWrapper;
import org.apache.flink.core.memory.DataOutputViewStreamWrapper;

import org.apache.flink.runtime.state.internal.InternalAggregatingState;
import org.rocksdb.ColumnFamilyHandle;
import org.rocksdb.RocksDBException;
import org.rocksdb.WriteOptions;

import java.io.IOException;
import java.util.Collection;

/**
 * An {@link AggregatingState} implementation that stores state in RocksDB.
 *
 * @param <K> The type of the key
 * @param <N> The type of the namespace
 * @param <T> The type of the values that aggregated into the state
 * @param <ACC> The type of the value stored in the state (the accumulator type)
 * @param <R> The type of the value returned from the state
 */
public class RocksDBAggregatingState<K, N, T, ACC, R>
	extends AbstractRocksDBState<K, N, AggregatingState<T, R>, AggregatingStateDescriptor<T, ACC, R>, ACC>
	implements InternalAggregatingState<N, T, R> {

	/** Serializer for the values */
	private final TypeSerializer<ACC> valueSerializer;

	/** User-specified aggregation function */
	private final AggregateFunction<T, ACC, R> aggFunction;

	/**
	 * We disable writes to the write-ahead-log here. We can't have these in the base class
	 * because JNI segfaults for some reason if they are.
	 */
	private final WriteOptions writeOptions;

	/**
	 * Creates a new {@code RocksDBFoldingState}.
	 *
	 * @param namespaceSerializer
	 *             The serializer for the namespace.
	 * @param stateDesc              
	 *             The state identifier for the state. This contains the state name and aggregation function.
	 */
	public RocksDBAggregatingState(
			ColumnFamilyHandle columnFamily,
			TypeSerializer<N> namespaceSerializer,
			AggregatingStateDescriptor<T, ACC, R> stateDesc,
			RocksDBKeyedStateBackend<K> backend) {

		super(columnFamily, namespaceSerializer, stateDesc, backend);

		this.valueSerializer = stateDesc.getSerializer();
		this.aggFunction = stateDesc.getAggregateFunction();

		writeOptions = new WriteOptions();
		writeOptions.setDisableWAL(true);
	}

	@Override
	public R get() throws IOException {
		try {
			// prepare the current key and namespace for RocksDB lookup
			writeCurrentKeyWithGroupAndNamespace();
			final byte[] key = keySerializationStream.toByteArray();

			// get the current value
			final byte[] valueBytes = backend.db.get(columnFamily, key);

			if (valueBytes == null) {
				return null;
			}

			ACC accumulator = valueSerializer.deserialize(new DataInputViewStreamWrapper(new ByteArrayInputStreamWithPos(valueBytes)));
			return aggFunction.getResult(accumulator);
		}
		catch (IOException | RocksDBException e) {
			throw new IOException("Error while retrieving value from RocksDB", e);
		}
	}

	@Override
	public void add(T value) throws IOException {
		try {
			// prepare the current key and namespace for RocksDB lookup
			writeCurrentKeyWithGroupAndNamespace();
			final byte[] key = keySerializationStream.toByteArray();
			keySerializationStream.reset();

			// get the current value
			final byte[] valueBytes = backend.db.get(columnFamily, key);

			// deserialize the current accumulator, or create a blank one
			final ACC accumulator = valueBytes == null ?
					aggFunction.createAccumulator() :
					valueSerializer.deserialize(new DataInputViewStreamWrapper(new ByteArrayInputStreamWithPos(valueBytes)));

			// aggregate the value into the accumulator
			aggFunction.add(value, accumulator);

			// serialize the new accumulator
			final DataOutputViewStreamWrapper out = new DataOutputViewStreamWrapper(keySerializationStream);
			valueSerializer.serialize(accumulator, out);

			// write the new value to RocksDB
			backend.db.put(columnFamily, writeOptions, key, keySerializationStream.toByteArray());
		}
		catch (IOException | RocksDBException e) {
			throw new IOException("Error while adding value to RocksDB", e);
		}
	}

	@Override
	public void mergeNamespaces(N target, Collection<N> sources) throws Exception {
		if (sources == null || sources.isEmpty()) {
			return;
		}

		// cache key and namespace
		final K key = backend.getCurrentKey();
		final int keyGroup = backend.getCurrentKeyGroupIndex();

		try {
			ACC current = null;

			// merge the sources to the target
			for (N source : sources) {
				if (source != null) {
					writeKeyWithGroupAndNamespace(
							keyGroup, key, source,
							keySerializationStream, keySerializationDataOutputView);
					
					final byte[] sourceKey = keySerializationStream.toByteArray();
					final byte[] valueBytes = backend.db.get(columnFamily, sourceKey);

					if (valueBytes != null) {
						ACC value = valueSerializer.deserialize(
								new DataInputViewStreamWrapper(new ByteArrayInputStreamWithPos(valueBytes)));

						if (current != null) {
							current = aggFunction.merge(current, value);
						}
						else {
							current = value;
						}
					}
				}
			}

			// if something came out of merging the sources, merge it or write it to the target
			if (current != null) {
				// create the target full-binary-key 
				writeKeyWithGroupAndNamespace(
						keyGroup, key, target,
						keySerializationStream, keySerializationDataOutputView);

				final byte[] targetKey = keySerializationStream.toByteArray();
				final byte[] targetValueBytes = backend.db.get(columnFamily, targetKey);

				if (targetValueBytes != null) {
					// target also had a value, merge
					ACC value = valueSerializer.deserialize(
							new DataInputViewStreamWrapper(new ByteArrayInputStreamWithPos(targetValueBytes)));

					current = aggFunction.merge(current, value);
				}

				// serialize the resulting value
				keySerializationStream.reset();
				valueSerializer.serialize(current, keySerializationDataOutputView);

				// write the resulting value
				backend.db.put(columnFamily, writeOptions, targetKey, keySerializationStream.toByteArray());
			}
		}
		catch (Exception e) {
			throw new Exception("Error while merging state in RocksDB", e);
		}
	}
}