/*

  * 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.aggregators;

 import com.google.common.base.Charsets;

 import java.io.IOException;

 import java.util.Map.Entry;

 import org.apache.giraph.conf.DefaultImmutableClassesGiraphConfigurable;

 import org.apache.hadoop.fs.FSDataOutputStream;

 import org.apache.hadoop.fs.FileSystem;

 import org.apache.hadoop.fs.Path;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.mapreduce.Mapper.Context;

 /**

  * Default implementation of {@link AggregatorWriter}. Each line consists of

  * text and contains the aggregator name, the aggregator value and the

  * aggregator class.

  */

 public class TextAggregatorWriter

     extends DefaultImmutableClassesGiraphConfigurable

     implements AggregatorWriter {

   /** The filename of the outputfile */

   public static final String FILENAME =

       "giraph.textAggregatorWriter.filename";

   /** Signal for "never write" frequency */

   public static final int NEVER = 0;

   /** Signal for "write only the final values" frequency */

   public static final int AT_THE_END = -1;

   /** Signal for "write values in every superstep" frequency */

   public static final int ALWAYS = 1;

   /** The frequency of writing:

    *  - NEVER: never write, files aren't created at all

    *  - AT_THE_END: aggregators are written only when the computation is over

    *  - int: i.e. 1 is every superstep, 2 every two supersteps and so on

    */

   public static final String FREQUENCY =

       "giraph.textAggregatorWriter.frequency";

   /** Default filename for dumping aggregator values */

   private static final String DEFAULT_FILENAME = "aggregatorValues";

   /** Handle to the outputfile */

   protected FSDataOutputStream output;

   /** Write every "frequency" supersteps */

   private int frequency;

   @Override

   @SuppressWarnings("rawtypes")

   public void initialize(Context context, long attempt) throws IOException {

     frequency = getConf().getInt(FREQUENCY, NEVER);

     String filename  = getConf().get(FILENAME, DEFAULT_FILENAME);

     if (frequency != NEVER) {

       Path p = new Path(filename + "_" + attempt);

       FileSystem fs = FileSystem.get(getConf());

       if (fs.exists(p)) {

         throw new RuntimeException("aggregatorWriter file already" +

             " exists: " + p.getName());

       }

       output = fs.create(p);

     }

   }

   @Override

   public void writeAggregator(

       Iterable<Entry<String, Writable>> aggregatorMap,

       long superstep) throws IOException {

     if (shouldWrite(superstep)) {

       for (Entry<String, Writable> entry : aggregatorMap) {

         byte[] bytes = aggregatorToString(entry.getKey(), entry.getValue(),

             superstep).getBytes(Charsets.UTF_8);

         output.write(bytes, 0, bytes.length);

       }

       output.flush();

     }

   }

   /**

    * Implements the way an aggregator is converted into a String.

    * Override this if you want to implement your own text format.

    *

    * @param aggregatorName Name of the aggregator

    * @param value Value of aggregator

    * @param superstep Current superstep

    * @return The String representation for the aggregator

    */

   protected String aggregatorToString(String aggregatorName,

       Writable value,

       long superstep) {

     return new StringBuilder("superstep=").append(superstep).append("\t")

         .append(aggregatorName).append("=").append(value).append("\n")

         .toString();

   }

   /**

    * Should write this superstep?

    *

    * @param superstep Superstep to check

    * @return True if should write, false otherwise

    */

   private boolean shouldWrite(long superstep) {

     return (frequency == AT_THE_END && superstep == LAST_SUPERSTEP) ||

         (frequency != NEVER && frequency != AT_THE_END &&

             superstep % frequency == 0);

   }

   @Override

   public void close() throws IOException {

     if (output != null) {

       output.close();

     }

   }

 }