/*

  * 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.reducers.impl;

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import org.apache.giraph.reducers.ReduceSameTypeOperation;

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

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

 import org.apache.giraph.writable.tuple.PairWritable;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Aggregating PairWritable<L, R>, by taking pair with

  * largest second value.

  *

  * @param <L> Type of the left value

  * @param <R> Type of the right value

  */

 public class MaxPairReducer<L extends Writable, R extends WritableComparable>

     extends ReduceSameTypeOperation<PairWritable<L, R>> {

   /** Left value TypeOps */

   private TypeOps<L> leftTypeOps;

   /** Right value TypeOps */

   private TypeOps<R> rightTypeOps;

   /** Constructor used for deserialization only */

   public MaxPairReducer() {

   }

   /**

    * Constructor

    * @param leftTypeOps Left value TypeOps

    * @param rightTypeOps Right value TypeOps

    */

   public MaxPairReducer(TypeOps<L> leftTypeOps, TypeOps<R> rightTypeOps) {

     this.leftTypeOps = leftTypeOps;

     this.rightTypeOps = rightTypeOps;

   }

   @Override

   public PairWritable<L, R> reduce(

       PairWritable<L, R> curValue, PairWritable<L, R> valueToReduce) {

     if (valueToReduce.getRight().compareTo(curValue.getRight()) > 0) {

       leftTypeOps.set(curValue.getLeft(), valueToReduce.getLeft());

       rightTypeOps.set(curValue.getRight(), valueToReduce.getRight());

     }

     return curValue;

   }

   @Override

   public PairWritable<L, R> createInitialValue() {

     return new PairWritable<L, R>(

         leftTypeOps.create(), rightTypeOps.create());

   }

   @Override

   public void write(DataOutput out) throws IOException {

     TypeOpsUtils.writeTypeOps(leftTypeOps, out);

     TypeOpsUtils.writeTypeOps(rightTypeOps, out);

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     leftTypeOps = TypeOpsUtils.readTypeOps(in);

     rightTypeOps = TypeOpsUtils.readTypeOps(in);

   }

 }