/*
    * 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();
    }
  }