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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.examples.java.graph;

import org.apache.flink.api.common.ProgramDescription;
import org.apache.flink.api.common.functions.FlatJoinFunction;
import org.apache.flink.api.common.functions.FlatMapFunction;
import org.apache.flink.api.common.functions.JoinFunction;
import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.java.aggregation.Aggregations;
import org.apache.flink.api.java.functions.FunctionAnnotation.ForwardedFields;
import org.apache.flink.api.java.functions.FunctionAnnotation.ForwardedFieldsFirst;
import org.apache.flink.api.java.functions.FunctionAnnotation.ForwardedFieldsSecond;
import org.apache.flink.api.java.tuple.Tuple1;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.util.Collector;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.operators.DeltaIteration;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.examples.java.graph.util.ConnectedComponentsData;

/**
 * An implementation of the connected components algorithm, using a delta iteration.
 * 
 * 
 * Initially, the algorithm assigns each vertex an unique ID. In each step, a vertex picks the minimum of its own ID and its
 * neighbors' IDs, as its new ID and tells its neighbors about its new ID. After the algorithm has completed, all vertices in the
 * same component will have the same ID.
 * 
 * 

 * A vertex whose component ID did not change needs not propagate its information in the next step. Because of that,
 * the algorithm is easily expressible via a delta iteration. We here model the solution set as the vertices with
 * their current component ids, and the workset as the changed vertices. Because we see all vertices initially as
 * changed, the initial workset and the initial solution set are identical. Also, the delta to the solution set
 * is consequently also the next workset.

 * 
 * 

 * Input files are plain text files and must be formatted as follows:
 * 

 * Vertices represented as IDs and separated by new-line characters.
 
 * For example "1\n2\n12\n42\n63" gives five vertices (1), (2), (12), (42), and (63).
 * 
Edges are represented as pairs for vertex IDs which are separated by space 
 * characters. Edges are separated by new-line characters.

 * For example "1 2\n2 12\n1 12\n42 63" gives four (undirected) edges (1)-(2), (2)-(12), (1)-(12), and (42)-(63).
 * 
 * 
 * 
 * Usage: ConnectedComponents <vertices path> <edges path> <result path> <max number of iterations>

 * If no parameters are provided, the program is run with default data from {@link ConnectedComponentsData} and 10 iterations. 
 * 
 * 

 * This example shows how to use:
 * 

 * Delta Iterations
 * 
Generic-typed Functions 
 * 
 */
@SuppressWarnings("serial")
public class ConnectedComponents implements ProgramDescription {
	
	// *************************************************************************
	//     PROGRAM
	// *************************************************************************
	
	public static void main(String... args) throws Exception {
		
		if(!parseParameters(args)) {
			return;
		}
		
		// set up execution environment
		ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
		
		// read vertex and edge data
		DataSet vertices = getVertexDataSet(env);
		DataSet> edges = getEdgeDataSet(env).flatMap(new UndirectEdge());
		
		// assign the initial components (equal to the vertex id)
		DataSet> verticesWithInitialId = vertices.map(new DuplicateValue());
				
		// open a delta iteration
		DeltaIteration, Tuple2> iteration =
				verticesWithInitialId.iterateDelta(verticesWithInitialId, maxIterations, 0);
		
		// apply the step logic: join with the edges, select the minimum neighbor, update if the component of the candidate is smaller
		DataSet> changes = iteration.getWorkset().join(edges).where(0).equalTo(0).with(new NeighborWithComponentIDJoin())
				.groupBy(0).aggregate(Aggregations.MIN, 1)
				.join(iteration.getSolutionSet()).where(0).equalTo(0)
				.with(new ComponentIdFilter());

		// close the delta iteration (delta and new workset are identical)
		DataSet> result = iteration.closeWith(changes, changes);
		
		// emit result
		if (fileOutput) {
			result.writeAsCsv(outputPath, "\n", " ");
			// execute program
			env.execute("Connected Components Example");
		} else {
			result.print();
		}
	}
	
	// *************************************************************************
	//     USER FUNCTIONS
	// *************************************************************************
	
	/**
	 * Function that turns a value into a 2-tuple where both fields are that value.
	 */
	@ForwardedFields("*->f0")
	public static final class DuplicateValue implements MapFunction> {
		
		@Override
		public Tuple2 map(T vertex) {
			return new Tuple2(vertex, vertex);
		}
	}
	
	/**
	 * Undirected edges by emitting for each input edge the input edges itself and an inverted version.
	 */
	public static final class UndirectEdge implements FlatMapFunction, Tuple2> {
		Tuple2 invertedEdge = new Tuple2();
		
		@Override
		public void flatMap(Tuple2 edge, Collector> out) {
			invertedEdge.f0 = edge.f1;
			invertedEdge.f1 = edge.f0;
			out.collect(edge);
			out.collect(invertedEdge);
		}
	}
	
	/**
	 * UDF that joins a (Vertex-ID, Component-ID) pair that represents the current component that
	 * a vertex is associated with, with a (Source-Vertex-ID, Target-VertexID) edge. The function
	 * produces a (Target-vertex-ID, Component-ID) pair.
	 */
	@ForwardedFieldsFirst("f1->f1")
	@ForwardedFieldsSecond("f1->f0")
	public static final class NeighborWithComponentIDJoin implements JoinFunction, Tuple2, Tuple2> {

		@Override
		public Tuple2 join(Tuple2 vertexWithComponent, Tuple2 edge) {
			return new Tuple2(edge.f1, vertexWithComponent.f1);
		}
	}
	


	@ForwardedFieldsFirst("*")
	public static final class ComponentIdFilter implements FlatJoinFunction, Tuple2, Tuple2> {

		@Override
		public void join(Tuple2 candidate, Tuple2 old, Collector> out) {
			if (candidate.f1 < old.f1) {
				out.collect(candidate);
			}
		}
	}



	@Override
	public String getDescription() {
		return "Parameters:    ";
	}
	
	// *************************************************************************
	//     UTIL METHODS
	// *************************************************************************
	
	private static boolean fileOutput = false;
	private static String verticesPath = null;
	private static String edgesPath = null;
	private static String outputPath = null;
	private static int maxIterations = 10;
	
	private static boolean parseParameters(String[] programArguments) {
		
		if(programArguments.length > 0) {
			// parse input arguments
			fileOutput = true;
			if(programArguments.length == 4) {
				verticesPath = programArguments[0];
				edgesPath = programArguments[1];
				outputPath = programArguments[2];
				maxIterations = Integer.parseInt(programArguments[3]);
			} else {
				System.err.println("Usage: ConnectedComponents    ");
				return false;
			}
		} else {
			System.out.println("Executing Connected Components 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: ConnectedComponents    ");
		}
		return true;
	}
	
	private static DataSet getVertexDataSet(ExecutionEnvironment env) {
		
		if(fileOutput) {
			return env.readCsvFile(verticesPath).types(Long.class)
						.map(
								new MapFunction, Long>() {
									public Long map(Tuple1 value) { return value.f0; }
								});
		} else {
			return ConnectedComponentsData.getDefaultVertexDataSet(env);
		}
	}
	
	private static DataSet> getEdgeDataSet(ExecutionEnvironment env) {
		
		if(fileOutput) {
			return env.readCsvFile(edgesPath).fieldDelimiter(" ").types(Long.class, Long.class);
		} else {
			return ConnectedComponentsData.getDefaultEdgeDataSet(env);
		}
	}
	
	
}