/*

  * 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.conf.LongConfOption;

 import org.apache.giraph.edge.Edge;

 import org.apache.giraph.graph.Vertex;

 import org.apache.hadoop.io.DoubleWritable;

 import org.apache.hadoop.io.FloatWritable;

 import org.apache.hadoop.io.LongWritable;

 import org.apache.log4j.Logger;

 import java.io.IOException;

 /**

  * Demonstrates the basic Pregel shortest paths implementation.

  */

 @Algorithm(

     name = "Shortest paths",

     description = "Finds all shortest paths from a selected vertex"

 )

 public class SimpleShortestPathsComputation extends BasicComputation<

     LongWritable, DoubleWritable, FloatWritable, DoubleWritable> {

   /** The shortest paths id */

   public static final LongConfOption SOURCE_ID =

       new LongConfOption("SimpleShortestPathsVertex.sourceId", 1,

           "The shortest paths id");

   /** Class logger */

   private static final Logger LOG =

       Logger.getLogger(SimpleShortestPathsComputation.class);

   /**

    * Is this vertex the source id?

    *

    * @param vertex Vertex

    * @return True if the source id

    */

   private boolean isSource(Vertex<LongWritable, ?, ?> vertex) {

     return vertex.getId().get() == SOURCE_ID.get(getConf());

   }

   @Override

   public void compute(

       Vertex<LongWritable, DoubleWritable, FloatWritable> vertex,

       Iterable<DoubleWritable> messages) throws IOException {

     if (getSuperstep() == 0) {

       vertex.setValue(new DoubleWritable(Double.MAX_VALUE));

     }

     double minDist = isSource(vertex) ? 0d : Double.MAX_VALUE;

     for (DoubleWritable message : messages) {

       minDist = Math.min(minDist, message.get());

     }

     if (LOG.isDebugEnabled()) {

       LOG.debug("Vertex " + vertex.getId() + " got minDist = " + minDist +

           " vertex value = " + vertex.getValue());

     }

     if (minDist < vertex.getValue().get()) {

       vertex.setValue(new DoubleWritable(minDist));

       for (Edge<LongWritable, FloatWritable> edge : vertex.getEdges()) {

         double distance = minDist + edge.getValue().get();

         if (LOG.isDebugEnabled()) {

           LOG.debug("Vertex " + vertex.getId() + " sent to " +

               edge.getTargetVertexId() + " = " + distance);

         }

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

       }

     }

     vertex.voteToHalt();

   }

 }