/*

  * 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.master;

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import org.apache.giraph.aggregators.Aggregator;

 import org.apache.giraph.conf.GiraphConfigurationSettable;

 import org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;

 import org.apache.giraph.reducers.ReduceSameTypeOperation;

 import org.apache.giraph.utils.ReflectionUtils;

 import org.apache.giraph.utils.WritableUtils;

 import org.apache.hadoop.io.Writable;

 /**

  * Translates aggregation operation to reduce operations.

  *

  * @param <A> Aggregation object type

  */

 public class AggregatorReduceOperation<A extends Writable>

     extends ReduceSameTypeOperation<A> implements GiraphConfigurationSettable {

   /** Aggregator class */

   private Class<? extends Aggregator<A>> aggregatorClass;

   /** Aggregator */

   private Aggregator<A> aggregator;

   /** Configuration */

   private ImmutableClassesGiraphConfiguration<?, ?, ?> conf;

   /** Constructor */

   public AggregatorReduceOperation() {

   }

   /**

    * Constructor

    * @param aggregatorClass Aggregator class

    * @param conf Configuration

    */

   public AggregatorReduceOperation(

       Class<? extends Aggregator<A>> aggregatorClass,

       ImmutableClassesGiraphConfiguration<?, ?, ?> conf) {

     this.aggregatorClass = aggregatorClass;

     this.conf = conf;

     initAggregator();

   }

   /** Initialize aggregator */

   private void initAggregator() {

     aggregator = ReflectionUtils.newInstance(aggregatorClass, conf);

     aggregator.setAggregatedValue(null);

   }

   @Override

   public A createInitialValue() {

     A agg = aggregator.createInitialValue();

     if (agg == null) {

       throw new IllegalStateException(

           "Aggregators initial value must not be null, but is for " +

           aggregator);

     }

     return agg;

   }

   /**

    * Creates copy of this object

    * @return copy

    */

   public AggregatorReduceOperation<A> createCopy() {

     return new AggregatorReduceOperation<>(aggregatorClass, conf);

   }

   public Class<? extends Aggregator<A>> getAggregatorClass() {

     return aggregatorClass;

   }

   @Override

   public synchronized A reduce(A curValue, A valueToReduce) {

     aggregator.setAggregatedValue(curValue);

     aggregator.aggregate(valueToReduce);

     A aggregated = aggregator.getAggregatedValue();

     aggregator.setAggregatedValue(null);

     return aggregated;

   }

   @Override

   public void setConf(ImmutableClassesGiraphConfiguration conf) {

     this.conf = conf;

   }

   @Override

   public void write(DataOutput out) throws IOException {

     WritableUtils.writeClass(aggregatorClass, out);

   }

   @Override

   public void readFields(DataInput in) throws IOException {

     aggregatorClass = WritableUtils.readClass(in);

     initAggregator();

   }

 }