/*
    * 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.ReduceOperation;
  import org.apache.giraph.writable.kryo.KryoWritableWrapper;
  
  /**
   * Reduce operation which wraps reduced value in KryoWritableWrapper,
   * so we don't need to worry about it being writable
   *
   * @param <S> Single value type
   * @param <R> Reduced value type
   */
  public abstract class KryoWrappedReduceOperation<S, R>
      implements ReduceOperation<S, KryoWritableWrapper<R>> {
    /**
     * Look at ReduceOperation.reduce.
     *
     * @param reduceInto Partial value into which to reduce and store the result
     * @param valueToReduce Single value to be reduced
     */
    public abstract void reduce(R reduceInto, S valueToReduce);
  
    /**
     * Look at ReduceOperation.reduceMerge.
     *
     * @param reduceInto Partial value into which to reduce and store the result
     * @param valueToReduce Partial value to be reduced
     */
    public abstract void reduceMerge(R reduceInto, R valueToReduce);
  
    /**
     * Look at ReduceOperation.createValue.
     *
     * @return Neutral value
     */
    public abstract R createValue();
  
    @Override
    public final KryoWritableWrapper<R> createInitialValue() {
      return new KryoWritableWrapper<>(createValue());
    }
  
    @Override
    public final KryoWritableWrapper<R> reduce(
        KryoWritableWrapper<R> wrapper, S value) {
      reduce(wrapper.get(), value);
      return wrapper;
    }
  
    @Override
    public final KryoWritableWrapper<R> reduceMerge(
        KryoWritableWrapper<R> wrapper,
        KryoWritableWrapper<R> wrapperToReduce) {
      reduceMerge(wrapper.get(), wrapperToReduce.get());
      return wrapper;
    }
  
    @Override
    public void write(DataOutput dataOutput) throws IOException {
    }
  
    @Override
    public void readFields(DataInput dataInput) throws IOException {
    }
  }