/*

  * 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.io.formats;

 import java.io.IOException;

 import org.apache.giraph.graph.Vertex;

 import org.apache.giraph.io.VertexOutputFormat;

 import org.apache.giraph.io.VertexWriter;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 import org.apache.hadoop.mapreduce.JobContext;

 import org.apache.hadoop.mapreduce.OutputCommitter;

 import org.apache.hadoop.mapreduce.RecordWriter;

 import org.apache.hadoop.mapreduce.TaskAttemptContext;

 import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;

 /**

  * Sequence file vertex output format. It allows to convert a vertex into a key

  * and value pair of desired types, and output the pair into a sequence file.

  * A subclass has to provide two conversion methods convertToSequenceFileKey()

  * and convertToSequenceFileValue().

  *

  * @param <I> Vertex id type

  * @param <V> Vertex value type

  * @param <E> Edge value type

  * @param <OK> Output key data type for a sequence file

  * @param <OV> Output value data type for a sequence file

  */

 public abstract class SequenceFileVertexOutputFormat<

   I extends WritableComparable,

   V extends Writable,

   E extends Writable,

   OK extends Writable,

   OV extends Writable>

   extends VertexOutputFormat<I, V, E> {

   /**

    * Output format of a sequence file that stores key-value pairs of the

    * desired types.

    */

   private SequenceFileOutputFormat<OK, OV> sequenceFileOutputFormat =

       new SequenceFileOutputFormat<OK, OV>();

   @Override

   public void checkOutputSpecs(JobContext context)

     throws IOException, InterruptedException {

     sequenceFileOutputFormat.checkOutputSpecs(context);

   }

   @Override

   public OutputCommitter getOutputCommitter(TaskAttemptContext context)

     throws IOException, InterruptedException {

     return sequenceFileOutputFormat.getOutputCommitter(context);

   }

   @Override

   public VertexWriter createVertexWriter(TaskAttemptContext

       context) throws IOException, InterruptedException {

     return new SequenceFileVertexWriter();

   }

   /**

    * Converts a vertex identifier into a sequence file key.

    * @param vertexId Vertex identifier.

    * @return Sequence file key.

    */

   protected abstract OK convertToSequenceFileKey(I vertexId);

   /**

    * Converts a vertex value into a sequence file value.

    * @param vertexValue Vertex value.

    * @return Sequence file value.

    */

   protected abstract OV convertToSequenceFileValue(V vertexValue);

   /**

    * Vertex writer that converts a vertex into a key-value pair and writes

    * the result into a sequence file for a context.

    */

   private class SequenceFileVertexWriter extends VertexWriter<I, V, E> {

     /**

      * A record writer that will write into a sequence file initialized for

      * a context.

      */

     private RecordWriter<OK, OV> recordWriter;

     @Override

     public void initialize(TaskAttemptContext context) throws IOException,

            InterruptedException {

       recordWriter = sequenceFileOutputFormat.getRecordWriter(context);

     }

     @Override

     public final void writeVertex(Vertex<I, V, E> vertex) throws

       IOException, InterruptedException {

       // Convert vertex id to type OK.

       OK outKey = convertToSequenceFileKey(vertex.getId());

       // Convert vertex value to type OV.

       OV outValue = convertToSequenceFileValue(vertex.getValue());

       recordWriter.write(outKey, outValue);

     }

     @Override

     public void close(TaskAttemptContext context) throws IOException,

         InterruptedException {

       recordWriter.close(context);

     }

   }

 }