/*
 * 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.runtime.iterative.task;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.flink.api.common.functions.Function;
import org.apache.flink.runtime.iterative.concurrent.SolutionSetUpdateBarrier;
import org.apache.flink.runtime.iterative.concurrent.SolutionSetUpdateBarrierBroker;
import org.apache.flink.runtime.iterative.concurrent.SuperstepKickoffLatch;
import org.apache.flink.runtime.iterative.concurrent.SuperstepKickoffLatchBroker;
import org.apache.flink.runtime.iterative.io.WorksetUpdateOutputCollector;
import org.apache.flink.util.Collector;

/**
 * An iteration tail, which runs a driver inside.
 * <p>
 * If the iteration state is updated, the output of this task will be send back to the {@link IterationHeadTask} via
 * a BackChannel for the workset -OR- a HashTable for the solution set. Therefore this
 * task must be scheduled on the same instance as the head. It's also possible for the tail to update *both* the workset
 * and the solution set.
 * <p>
 * If there is a separate solution set tail, the iteration head has to make sure to wait for it to finish.
 */
public class IterationTailTask<S extends Function, OT> extends AbstractIterativeTask<S, OT> {

	private static final Logger log = LoggerFactory.getLogger(IterationTailTask.class);

	private SolutionSetUpdateBarrier solutionSetUpdateBarrier;

	private WorksetUpdateOutputCollector<OT> worksetUpdateOutputCollector;
	

	@Override
	protected void initialize() throws Exception {
		super.initialize();

		// sanity check: the tail has to update either the workset or the solution set
		if (!isWorksetUpdate && !isSolutionSetUpdate) {
			throw new RuntimeException("The iteration tail doesn't update workset or the solution set.");
		}

		// set the last output collector of this task to reflect the iteration tail state update:
		// a) workset update,
		// b) solution set update, or
		// c) merged workset and solution set update

		Collector<OT> outputCollector = null;
		if (isWorksetUpdate) {
			outputCollector = createWorksetUpdateOutputCollector();

			// we need the WorksetUpdateOutputCollector separately to count the collected elements
			if (isWorksetIteration) {
				worksetUpdateOutputCollector = (WorksetUpdateOutputCollector<OT>) outputCollector;
			}
		}

		if (isSolutionSetUpdate) {
			if (isWorksetIteration) {
				outputCollector = createSolutionSetUpdateOutputCollector(outputCollector);
			}
			// Bulk iteration with termination criterion
			else {
				outputCollector = new Collector<OT>() {
					@Override
					public void collect(OT record) {}
					@Override
					public void close() {}
				};
			}

			if (!isWorksetUpdate) {
				solutionSetUpdateBarrier = SolutionSetUpdateBarrierBroker.instance().get(brokerKey());
			}
		}

		setLastOutputCollector(outputCollector);
	}

	@Override
	public void run() throws Exception {
		
		SuperstepKickoffLatch nextSuperStepLatch = SuperstepKickoffLatchBroker.instance().get(brokerKey());
		
		while (this.running && !terminationRequested()) {

			if (log.isInfoEnabled()) {
				log.info(formatLogString("starting iteration [" + currentIteration() + "]"));
			}

			super.run();

			// check if termination was requested
			verifyEndOfSuperstepState();

			if (isWorksetUpdate && isWorksetIteration) {
				// aggregate workset update element count
				long numCollected = worksetUpdateOutputCollector.getElementsCollectedAndReset();
				worksetAggregator.aggregate(numCollected);

			}

			if (log.isInfoEnabled()) {
				log.info(formatLogString("finishing iteration [" + currentIteration() + "]"));
			}
			
			if (isWorksetUpdate) {
				// notify iteration head if responsible for workset update
				worksetBackChannel.notifyOfEndOfSuperstep();
			} else if (isSolutionSetUpdate) {
				// notify iteration head if responsible for solution set update
				solutionSetUpdateBarrier.notifySolutionSetUpdate();
			}

			boolean terminate = nextSuperStepLatch.awaitStartOfSuperstepOrTermination(currentIteration() + 1);
			if (terminate) {
				requestTermination();
			}
			else {
				incrementIterationCounter();
			}
		}
	}
}