/*

  * 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.combiner;

 import org.apache.giraph.types.ops.NumericTypeOps;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Keeps only the message with minimum value.

  *

  * @param <I> Vertex id

  * @param <M> Message

  */

 public class MinMessageCombiner<I extends WritableComparable,

     M extends Writable> implements MessageCombiner<I, M> {

   /** Numeric type ops for the value to combine */

   private final NumericTypeOps<M> numTypeOps;

   /**

    * Combiner

    *

    * @param numTypeOps Type ops to use

    */

   public MinMessageCombiner(NumericTypeOps<M> numTypeOps) {

     this.numTypeOps = numTypeOps;

   }

   @Override

   public void combine(I vertexId, M originalMessage, M messageToCombine) {

     if (numTypeOps.compare(originalMessage, messageToCombine) > 0) {

       numTypeOps.set(originalMessage, messageToCombine);

     }

   }

   @Override

   public M createInitialMessage() {

     return this.numTypeOps.createMaxPositiveValue();

   }

 }