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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.example;

import org.apache.flink.api.common.ProgramDescription;
import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.graph.Edge;
import org.apache.flink.graph.Graph;
import org.apache.flink.graph.Vertex;
import org.apache.flink.graph.example.utils.SingleSourceShortestPathsData;
import org.apache.flink.graph.spargel.MessageIterator;
import org.apache.flink.graph.spargel.MessagingFunction;
import org.apache.flink.graph.spargel.VertexUpdateFunction;
import org.apache.flink.graph.utils.Tuple3ToEdgeMap;

/**
 * This example shows how to use Gelly's vertex-centric iterations.
 * 
 * It is an implementation of the Single-Source-Shortest-Paths algorithm.
 * For a gather-sum-apply implementation of the same algorithm, please refer to {@link GSASingleSourceShortestPaths}. 
 *
 * The input file is a plain text file and must be formatted as follows:
 * Edges are represented by tuples of srcVertexId, trgVertexId, distance which are
 * separated by tabs. Edges themselves are separated by newlines.
 * For example: 1\t2\t0.1\n1\t3\t1.4\n defines two edges,
 * edge 1-2 with distance 0.1, and edge 1-3 with distance 1.4.
 *
 * If no parameters are provided, the program is run with default data from
 * {@link org.apache.flink.graph.example.utils.SingleSourceShortestPathsData}
 */
public class SingleSourceShortestPaths implements ProgramDescription {

	public static void main(String[] args) throws Exception {

		if (!parseParameters(args)) {
			return;
		}

		ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();

		DataSet> edges = getEdgesDataSet(env);

		Graph graph = Graph.fromDataSet(edges, new InitVertices(srcVertexId), env);

		// Execute the vertex-centric iteration
		Graph result = graph.runVertexCentricIteration(
				new VertexDistanceUpdater(), new MinDistanceMessenger(), maxIterations);

		// Extract the vertices as the result
		DataSet> singleSourceShortestPaths = result.getVertices();

		// emit result
		if (fileOutput) {
			singleSourceShortestPaths.writeAsCsv(outputPath, "\n", ",");

			// since file sinks are lazy, we trigger the execution explicitly
			env.execute("Single Source Shortest Paths Example");
		} else {
			singleSourceShortestPaths.print();
		}

	}

	// --------------------------------------------------------------------------------------------
	//  Single Source Shortest Path UDFs
	// --------------------------------------------------------------------------------------------

	@SuppressWarnings("serial")
	private static final class InitVertices implements MapFunction{

		private long srcId;

		public InitVertices(long srcId) {
			this.srcId = srcId;
		}

		public Double map(Long id) {
			if (id.equals(srcId)) {
				return 0.0;
			}
			else {
				return Double.POSITIVE_INFINITY;
			}
		}
	}

	/**
	 * Function that updates the value of a vertex by picking the minimum
	 * distance from all incoming messages.
	 */
	@SuppressWarnings("serial")
	public static final class VertexDistanceUpdater extends VertexUpdateFunction {

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

			Double minDistance = Double.MAX_VALUE;

			for (double msg : inMessages) {
				if (msg < minDistance) {
					minDistance = msg;
				}
			}

			if (vertex.getValue() > minDistance) {
				setNewVertexValue(minDistance);
			}
		}
	}

	/**
	 * Distributes the minimum distance associated with a given vertex among all
	 * the target vertices summed up with the edge's value.
	 */
	@SuppressWarnings("serial")
	public static final class MinDistanceMessenger extends MessagingFunction {

		@Override
		public void sendMessages(Vertex vertex) {
			for (Edge edge : getEdges()) {
				sendMessageTo(edge.getTarget(), vertex.getValue() + edge.getValue());
			}
		}
	}

	// ******************************************************************************************************************
	// UTIL METHODS
	// ******************************************************************************************************************

	private static boolean fileOutput = false;

	private static Long srcVertexId = 1l;

	private static String edgesInputPath = null;

	private static String outputPath = null;

	private static int maxIterations = 5;

	private static boolean parseParameters(String[] args) {

		if(args.length > 0) {
			if(args.length != 4) {
				System.err.println("Usage: SingleSourceShortestPaths " +
						"   ");
				return false;
			}

			fileOutput = true;
			srcVertexId = Long.parseLong(args[0]);
			edgesInputPath = args[1];
			outputPath = args[2];
			maxIterations = Integer.parseInt(args[3]);
		} else {
				System.out.println("Executing Single Source Shortest Paths example "
						+ "with default parameters and built-in default data.");
				System.out.println("  Provide parameters to read input data from files.");
				System.out.println("  See the documentation for the correct format of input files.");
				System.out.println("Usage: SingleSourceShortestPaths " +
						"   ");
		}
		return true;
	}

	private static DataSet> getEdgesDataSet(ExecutionEnvironment env) {
		if (fileOutput) {
			return env.readCsvFile(edgesInputPath)
					.lineDelimiter("\n")
					.fieldDelimiter("\t")
					.types(Long.class, Long.class, Double.class)
					.map(new Tuple3ToEdgeMap());
		} else {
			return SingleSourceShortestPathsData.getDefaultEdgeDataSet(env);
		}
	}

	@Override
	public String getDescription() {
		return "Vertex-centric Single Source Shortest Paths";
	}
}