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/*
 * 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.library;

import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.functions.FunctionAnnotation.ForwardedFields;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.graph.Edge;
import org.apache.flink.graph.Graph;
import org.apache.flink.graph.GraphAlgorithm;
import org.apache.flink.graph.Vertex;
import org.apache.flink.graph.spargel.MessageIterator;
import org.apache.flink.graph.spargel.MessagingFunction;
import org.apache.flink.graph.spargel.VertexUpdateFunction;

import java.util.Map;
import java.util.TreeMap;

/**
 * Community Detection Algorithm.
 *
 * The Vertex values of the input Graph provide the initial label assignments.
 * 
 * Initially, each vertex is assigned a tuple formed of its own initial value along with a score equal to 1.0.
 * The vertices propagate their labels and max scores in iterations, each time adopting the label with the
 * highest score from the list of received messages. The chosen label is afterwards re-scored using the fraction
 * delta/the superstep number. Delta is passed as a parameter and has 0.5 as a default value.
 * 
 * @param  the Vertex ID type 
 *
 */
public class CommunityDetection implements GraphAlgorithm> {

	private Integer maxIterations;

	private Double delta;

	/**
	 * Creates a new Community Detection algorithm instance.
	 * The algorithm converges when vertices no longer update their value
	 * or when the maximum number of iterations is reached.
	 * 
	 * @see 
	 * Towards real-time community detection in large networks
	 * 
	 * @param maxIterations The maximum number of iterations to run.
	 * @param delta The hop attenuation parameter. Its default value is 0.5.  
	 */
	public CommunityDetection(Integer maxIterations, Double delta) {

		this.maxIterations = maxIterations;
		this.delta = delta;
	}

	@Override
	public Graph run(Graph graph) {

		DataSet>> initializedVertices = graph.getVertices()
				.map(new AddScoreToVertexValuesMapper());

		Graph, Double> graphWithScoredVertices =
				Graph.fromDataSet(initializedVertices, graph.getEdges(), graph.getContext()).getUndirected();

		return graphWithScoredVertices.runScatterGatherIteration(new VertexLabelUpdater(delta),
				new LabelMessenger(), maxIterations)
				.mapVertices(new RemoveScoreFromVertexValuesMapper());
	}

	@SuppressWarnings("serial")
	public static final class VertexLabelUpdater extends VertexUpdateFunction<
		K, Tuple2, Tuple2> {

		private Double delta;

		public VertexLabelUpdater(Double delta) {
			this.delta = delta;
		}

		@Override
		public void updateVertex(Vertex> vertex,
								MessageIterator> inMessages) throws Exception {

			// we would like these two maps to be ordered
			Map receivedLabelsWithScores = new TreeMap();
			Map labelsWithHighestScore = new TreeMap();

			for (Tuple2 message : inMessages) {
				// split the message into received label and score
				Long receivedLabel = message.f0;
				Double receivedScore = message.f1;

				// if the label was received before
				if (receivedLabelsWithScores.containsKey(receivedLabel)) {
					Double newScore = receivedScore + receivedLabelsWithScores.get(receivedLabel);
					receivedLabelsWithScores.put(receivedLabel, newScore);
				} else {
					// first time we see the label
					receivedLabelsWithScores.put(receivedLabel, receivedScore);
				}

				// store the labels with the highest scores
				if (labelsWithHighestScore.containsKey(receivedLabel)) {
					Double currentScore = labelsWithHighestScore.get(receivedLabel);
					if (currentScore < receivedScore) {
						// record the highest score
						labelsWithHighestScore.put(receivedLabel, receivedScore);
					}
				} else {
					// first time we see this label
					labelsWithHighestScore.put(receivedLabel, receivedScore);
				}
			}

			if(receivedLabelsWithScores.size() > 0) {
				// find the label with the highest score from the ones received
				Double maxScore = -Double.MAX_VALUE;
				Long maxScoreLabel = vertex.getValue().f0;
				for (Long curLabel : receivedLabelsWithScores.keySet()) {

					if (receivedLabelsWithScores.get(curLabel) > maxScore) {
						maxScore = receivedLabelsWithScores.get(curLabel);
						maxScoreLabel = curLabel;
					}
				}

				// find the highest score of maxScoreLabel
				Double highestScore = labelsWithHighestScore.get(maxScoreLabel);
				// re-score the new label
				if (maxScoreLabel != vertex.getValue().f0) {
					highestScore -= delta / getSuperstepNumber();
				}
				// else delta = 0
				// update own label
				setNewVertexValue(new Tuple2(maxScoreLabel, highestScore));
			}
		}
	}

	@SuppressWarnings("serial")
	public static final class LabelMessenger extends MessagingFunction,
			Tuple2, Double> {

		@Override
		public void sendMessages(Vertex> vertex) throws Exception {

			for(Edge edge : getEdges()) {
				sendMessageTo(edge.getTarget(), new Tuple2(vertex.getValue().f0,
						vertex.getValue().f1 * edge.getValue()));
			}
		}
	}

	@SuppressWarnings("serial")
	@ForwardedFields("f0")
	public static final class AddScoreToVertexValuesMapper implements MapFunction<
		Vertex, Vertex>> {

		public Vertex> map(Vertex vertex) {
			return new Vertex>(
					vertex.getId(), new Tuple2(vertex.getValue(), 1.0));
		}
	}

	@SuppressWarnings("serial")
	public static final class RemoveScoreFromVertexValuesMapper implements MapFunction<
		Vertex>, Long> {

		@Override
		public Long map(Vertex> vertex) throws Exception {
			return vertex.getValue().f0;
		}
	}
}