/*
    * 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.benchmark;
  
  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;
  
  /**
   * Shortest paths algorithm.
   */
  public class ShortestPathsComputation extends BasicComputation<LongWritable,
      DoubleWritable, DoubleWritable, DoubleWritable> {
    /** Source id. */
    public static final String SOURCE_ID =
        "giraph.shortestPathsBenchmark.sourceId";
    /** Default source id. */
    public static final long SOURCE_ID_DEFAULT = 1;
  
    /**
     * Check if vertex is source from which to calculate shortest paths.
     *
     * @param vertex Vertex
     * @return True iff vertex is source for shortest paths
     */
    private boolean isSource(
        Vertex<LongWritable, DoubleWritable, DoubleWritable> vertex) {
      return vertex.getId().get() ==
          getConf().getLong(SOURCE_ID, SOURCE_ID_DEFAULT);
    }
  
    @Override
    public void compute(
        Vertex<LongWritable, DoubleWritable, DoubleWritable> 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 (minDist < vertex.getValue().get()) {
        vertex.setValue(new DoubleWritable(minDist));
        for (Edge<LongWritable, DoubleWritable> edge : vertex.getEdges()) {
          double distance = minDist + edge.getValue().get();
          sendMessage(edge.getTargetVertexId(),
              new DoubleWritable(distance));
        }
      }
  
      vertex.voteToHalt();
    }
  }