/*

  * 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.giraph.examples;

 import org.apache.giraph.graph.BasicComputation;

 import org.apache.giraph.edge.Edge;

 import org.apache.giraph.graph.Vertex;

 import org.apache.hadoop.io.DoubleWritable;

 import org.apache.hadoop.io.LongWritable;

 import java.io.IOException;

 /**

  * Simple function to return the out degree for each vertex.

  */

 @Algorithm(

     name = "Indegree Count"

 )

 public class SimpleInDegreeCountComputation extends BasicComputation<

   LongWritable, LongWritable, DoubleWritable, DoubleWritable> {

   @Override

   public void compute(

       Vertex<LongWritable, LongWritable, DoubleWritable> vertex,

       Iterable<DoubleWritable> messages) throws IOException {

     if (getSuperstep() == 0) {

       Iterable<Edge<LongWritable, DoubleWritable>> edges = vertex.getEdges();

       for (Edge<LongWritable, DoubleWritable> edge : edges) {

         sendMessage(edge.getTargetVertexId(), new DoubleWritable(1.0));

       }

     } else {

       long sum = 0;

       for (DoubleWritable message : messages) {

         sum++;

       }

       LongWritable vertexValue = vertex.getValue();

       vertexValue.set(sum);

       vertex.setValue(vertexValue);

       vertex.voteToHalt();

     }

   }

 }