/*
 * 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.graph.asm.dataset;

import org.apache.flink.api.common.accumulators.SerializedListAccumulator;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.graph.AnalyticHelper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * Collect the elements of a {@link DataSet} into a {@link List}.
 *
 * @param <T> element type
 */
public class Collect<T>
extends AbstractDataSetAnalytic<T, List<T>> {

	private static final String COLLECT = "collect";

	private CollectHelper<T> collectHelper;

	private TypeSerializer<T> serializer;

	@Override
	public Collect<T> run(DataSet<T> input)
			throws Exception {
		super.run(input);

		ExecutionEnvironment env = input.getExecutionEnvironment();
		serializer = input.getType().createSerializer(env.getConfig());

		collectHelper = new CollectHelper<>(serializer);

		input
			.output(collectHelper)
				.name("Collect");

		return this;
	}

	@Override
	public List<T> getResult() {
		ArrayList<byte[]> accResult = collectHelper.getAccumulator(env, COLLECT);
		if (accResult != null) {
			try {
				return SerializedListAccumulator.deserializeList(accResult, serializer);
			} catch (ClassNotFoundException e) {
				throw new RuntimeException("Cannot find type class of collected data type", e);
			} catch (IOException e) {
				throw new RuntimeException("Serialization error while deserializing collected data", e);
			}
		} else {
			throw new RuntimeException("Unable to retrieve the DataSet");
		}
	}

	/**
	 * Helper class to collect elements into a serialized list.
	 *
	 * @param <U> element type
	 */
	private static class CollectHelper<U>
	extends AnalyticHelper<U> {
		private SerializedListAccumulator<U> accumulator;

		private final TypeSerializer<U> serializer;

		public CollectHelper(TypeSerializer<U> serializer) {
			this.serializer = serializer;
		}

		@Override
		public void open(int taskNumber, int numTasks)  {
			this.accumulator = new SerializedListAccumulator<>();
		}

		@Override
		public void writeRecord(U record) throws IOException {
			accumulator.add(record, serializer);
		}

		@Override
		public void close() throws IOException {
			addAccumulator(COLLECT, accumulator);
		}
	}
}