/*
 * 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.streaming.runtime.tasks;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;

import org.apache.flink.annotation.Internal;
import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
import org.apache.flink.streaming.api.operators.Output;
import org.apache.flink.streaming.api.watermark.Watermark;
import org.apache.flink.streaming.runtime.io.BlockingQueueBroker;
import org.apache.flink.streaming.runtime.streamrecord.LatencyMarker;
import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
import org.apache.flink.util.OutputTag;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A special {@link StreamTask} that is used for executing feedback edges. This is used in
 * combination with {@link StreamIterationHead}.
 */
@Internal
public class StreamIterationTail<IN> extends OneInputStreamTask<IN, IN> {

	private static final Logger LOG = LoggerFactory.getLogger(StreamIterationTail.class);

	@Override
	public void init() throws Exception {

		final String iterationId = getConfiguration().getIterationId();
		if (iterationId == null || iterationId.length() == 0) {
			throw new Exception("Missing iteration ID in the task configuration");
		}

		final String brokerID = StreamIterationHead.createBrokerIdString(getEnvironment().getJobID(), iterationId,
				getEnvironment().getTaskInfo().getIndexOfThisSubtask());

		final long iterationWaitTime = getConfiguration().getIterationWaitTime();

		LOG.info("Iteration tail {} trying to acquire feedback queue under {}", getName(), brokerID);

		@SuppressWarnings("unchecked")
		BlockingQueue<StreamRecord<IN>> dataChannel =
				(BlockingQueue<StreamRecord<IN>>) BlockingQueueBroker.INSTANCE.get(brokerID);

		LOG.info("Iteration tail {} acquired feedback queue {}", getName(), brokerID);

		this.headOperator = new RecordPusher<>();
		this.headOperator.setup(this, getConfiguration(), new IterationTailOutput<>(dataChannel, iterationWaitTime));

		// call super.init() last because that needs this.headOperator to be set up
		super.init();
	}

	private static class RecordPusher<IN> extends AbstractStreamOperator<IN> implements OneInputStreamOperator<IN, IN> {

		private static final long serialVersionUID = 1L;

		@Override
		public void processElement(StreamRecord<IN> record) throws Exception {
			output.collect(record);
		}

		@Override
		public void processWatermark(Watermark mark) {
			// ignore
		}

		@Override
		public void processLatencyMarker(LatencyMarker latencyMarker) throws Exception {
			// ignore
		}
	}

	private static class IterationTailOutput<IN> implements Output<StreamRecord<IN>> {

		@SuppressWarnings("NonSerializableFieldInSerializableClass")
		private final BlockingQueue<StreamRecord<IN>> dataChannel;

		private final long iterationWaitTime;

		private final boolean shouldWait;

		IterationTailOutput(BlockingQueue<StreamRecord<IN>> dataChannel, long iterationWaitTime) {
			this.dataChannel = dataChannel;
			this.iterationWaitTime = iterationWaitTime;
			this.shouldWait =  iterationWaitTime > 0;
		}

		@Override
		public void emitWatermark(Watermark mark) {
		}

		@Override
		public void emitLatencyMarker(LatencyMarker latencyMarker) {
		}

		@Override
		public void collect(StreamRecord<IN> record) {
			try {
				if (shouldWait) {
					dataChannel.offer(record, iterationWaitTime, TimeUnit.MILLISECONDS);
				}
				else {
					dataChannel.put(record);
				}
			} catch (InterruptedException e) {
				throw new RuntimeException(e);
			}
		}

		@Override
		public <X> void collect(OutputTag<X> outputTag, StreamRecord<X> record) {
			throw new UnsupportedOperationException("Side outputs not used in iteration tail");

		}

		@Override
		public void close() {
		}
	}
}