/**
 * 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.hadoop.mapreduce;

import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.Arrays;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.MiniDFSCluster;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.MiniMRCluster;
import org.apache.hadoop.mapred.Utils;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.LazyOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.junit.Test;

import static org.junit.Assert.assertTrue;

/**
 * A JUnit test to test the Map-Reduce framework's feature to create part
 * files only if there is an explicit output.collect. This helps in preventing
 * 0 byte files
 */
public class TestMapReduceLazyOutput {
  private static final int NUM_HADOOP_WORKERS = 3;
  private static final int NUM_MAPS_PER_NODE = 2;
  private static final Path INPUTPATH = new Path("/testlazy/input");

  private static final List<String> INPUTLIST =
    Arrays.asList("All","Roads","Lead","To","Hadoop");

  /**
   * Test mapper.
   */
  public static class TestMapper
  extends Mapper<LongWritable, Text, LongWritable, Text>{

    public void map(LongWritable key, Text value, Context context
    ) throws IOException, InterruptedException {
      String id = context.getTaskAttemptID().toString();
      // Mapper 0 does not output anything
      if (!id.endsWith("0_0")) {
        context.write(key, value);
      }
    }
  }

  /**
   * Test Reducer.
   */
  public static class TestReducer
  extends Reducer<LongWritable,Text,LongWritable,Text> {

    public void reduce(LongWritable key, Iterable<Text> values,
        Context context) throws IOException, InterruptedException {
      String id = context.getTaskAttemptID().toString();
      // Reducer 0 does not output anything
      if (!id.endsWith("0_0")) {
        for (Text val: values) {
          context.write(key, val);
        }
      }
    }
  }

  private static void runTestLazyOutput(Configuration conf, Path output,
      int numReducers, boolean createLazily)
  throws Exception {
    Job job = Job.getInstance(conf, "Test-Lazy-Output");

    FileInputFormat.setInputPaths(job, INPUTPATH);
    FileOutputFormat.setOutputPath(job, output);

    job.setJarByClass(TestMapReduceLazyOutput.class);
    job.setInputFormatClass(TextInputFormat.class);
    job.setOutputKeyClass(LongWritable.class);
    job.setOutputValueClass(Text.class);
    job.setNumReduceTasks(numReducers);

    job.setMapperClass(TestMapper.class);
    job.setReducerClass(TestReducer.class);

    if (createLazily) {
      LazyOutputFormat.setOutputFormatClass(job, TextOutputFormat.class);
    } else {
      job.setOutputFormatClass(TextOutputFormat.class);
    }
    assertTrue(job.waitForCompletion(true));
  }

  public void createInput(FileSystem fs, int numMappers) throws Exception {
    for (int i =0; i < numMappers; i++) {
      OutputStream os = fs.create(new Path(INPUTPATH,
        "text" + i + ".txt"));
      Writer wr = new OutputStreamWriter(os);
      for(String inp : INPUTLIST) {
        wr.write(inp+"\n");
      }
      wr.close();
    }
  }

  @Test
  public void testLazyOutput() throws Exception {
    MiniDFSCluster dfs = null;
    MiniMRCluster mr = null;
    FileSystem fileSys = null;
    try {
      Configuration conf = new Configuration();

      // Start the mini-MR and mini-DFS clusters
      dfs = new MiniDFSCluster.Builder(conf).numDataNodes(NUM_HADOOP_WORKERS)
          .build();
      fileSys = dfs.getFileSystem();
      mr = new MiniMRCluster(NUM_HADOOP_WORKERS,
                             fileSys.getUri().toString(), 1);

      int numReducers = 2;
      int numMappers = NUM_HADOOP_WORKERS * NUM_MAPS_PER_NODE;

      createInput(fileSys, numMappers);
      Path output1 = new Path("/testlazy/output1");

      // Test 1.
      runTestLazyOutput(mr.createJobConf(), output1,
          numReducers, true);

      Path[] fileList =
        FileUtil.stat2Paths(fileSys.listStatus(output1,
            new Utils.OutputFileUtils.OutputFilesFilter()));
      for(int i=0; i < fileList.length; ++i) {
        System.out.println("Test1 File list[" + i + "]" + ": "+ fileList[i]);
      }
      assertTrue(fileList.length == (numReducers - 1));

      // Test 2. 0 Reducers, maps directly write to the output files
      Path output2 = new Path("/testlazy/output2");
      runTestLazyOutput(mr.createJobConf(), output2, 0, true);

      fileList =
        FileUtil.stat2Paths(fileSys.listStatus(output2,
            new Utils.OutputFileUtils.OutputFilesFilter()));
      for(int i=0; i < fileList.length; ++i) {
        System.out.println("Test2 File list[" + i + "]" + ": "+ fileList[i]);
      }

      assertTrue(fileList.length == numMappers - 1);

      // Test 3. 0 Reducers, but flag is turned off
      Path output3 = new Path("/testlazy/output3");
      runTestLazyOutput(mr.createJobConf(), output3, 0, false);

      fileList =
        FileUtil.stat2Paths(fileSys.listStatus(output3,
            new Utils.OutputFileUtils.OutputFilesFilter()));
      for(int i=0; i < fileList.length; ++i) {
        System.out.println("Test3 File list[" + i + "]" + ": "+ fileList[i]);
      }

      assertTrue(fileList.length == numMappers);

    } finally {
      if (dfs != null) { dfs.shutdown(); }
      if (mr != null) { mr.shutdown();
      }
    }
  }

}
