/*

  * 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.DoubleTypeOps;

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

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

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

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

 import org.apache.hadoop.io.DoubleWritable;

 import org.apache.hadoop.io.FloatWritable;

 import org.apache.hadoop.io.IntWritable;

 import org.apache.hadoop.io.LongWritable;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Message combiner which calculates max of all messages.

  *

  * @param <M> Message type

  */

 public class MaxMessageCombiner<M extends WritableComparable>

     implements MessageCombiner<WritableComparable, M> {

   /** DoubleWritable specialization */

   public static final MaxMessageCombiner<DoubleWritable> DOUBLE =

       new MaxMessageCombiner<>(DoubleTypeOps.INSTANCE);

   /** DoubleWritable specialization */

   public static final MaxMessageCombiner<FloatWritable> FLOAT =

       new MaxMessageCombiner<>(FloatTypeOps.INSTANCE);

   /** LongWritable specialization */

   public static final MaxMessageCombiner<LongWritable> LONG =

       new MaxMessageCombiner<>(LongTypeOps.INSTANCE);

   /** IntWritable specialization */

   public static final MaxMessageCombiner<IntWritable> INT =

       new MaxMessageCombiner<>(IntTypeOps.INSTANCE);

   /** Value type operations */

   private final NumericTypeOps<M> typeOps;

   /**

    * Constructor

    * @param typeOps Value type operations

    */

   public MaxMessageCombiner(NumericTypeOps<M> typeOps) {

     this.typeOps = typeOps;

   }

   @Override

   public void combine(

       WritableComparable vertexIndex, M originalMessage, M messageToCombine) {

     if (originalMessage.compareTo(messageToCombine) < 0) {

       typeOps.set(originalMessage, messageToCombine);

     }

   }

   @Override

   public M createInitialMessage() {

     return typeOps.createZero();

   }

 }