/**
    * 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.hbase.mapreduce;
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  import java.lang.reflect.Method;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
  import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
  import org.apache.hadoop.io.Writable;
  import org.apache.hadoop.mapreduce.InputFormat;
  import org.apache.hadoop.mapreduce.InputSplit;
  import org.apache.hadoop.mapreduce.Job;
  import org.apache.hadoop.mapreduce.JobContext;
  import org.apache.hadoop.mapreduce.RecordReader;
  import org.apache.hadoop.mapreduce.TaskAttemptContext;
  
  import com.google.common.annotations.VisibleForTesting;
  
  /**
   * TableSnapshotInputFormat allows a MapReduce job to run over a table snapshot. The job
   * bypasses HBase servers, and directly accesses the underlying files (hfile, recovered edits,
   * wals, etc) directly to provide maximum performance. The snapshot is not required to be
   * restored to the live cluster or cloned. This also allows to run the mapreduce job from an
   * online or offline hbase cluster. The snapshot files can be exported by using the
   * {@link org.apache.hadoop.hbase.snapshot.ExportSnapshot} tool, to a pure-hdfs cluster, 
   * and this InputFormat can be used to run the mapreduce job directly over the snapshot files. 
   * The snapshot should not be deleted while there are jobs reading from snapshot files.
   * <p>
   * Usage is similar to TableInputFormat, and
   * {@link TableMapReduceUtil#initTableSnapshotMapperJob(String, Scan, Class, Class, Class, Job,
   *   boolean, Path)}
   * can be used to configure the job.
   * <pre>{@code
   * Job job = new Job(conf);
   * Scan scan = new Scan();
   * TableMapReduceUtil.initTableSnapshotMapperJob(snapshotName,
   *      scan, MyTableMapper.class, MyMapKeyOutput.class,
   *      MyMapOutputValueWritable.class, job, true);
   * }
   * </pre>
   * <p>
   * Internally, this input format restores the snapshot into the given tmp directory. Similar to
   * {@link TableInputFormat} an InputSplit is created per region. The region is opened for reading
   * from each RecordReader. An internal RegionScanner is used to execute the 
   * {@link org.apache.hadoop.hbase.CellScanner} obtained from the user.
   * <p>
   * HBase owns all the data and snapshot files on the filesystem. Only the 'hbase' user can read from
   * snapshot files and data files.
   * To read from snapshot files directly from the file system, the user who is running the MR job
   * must have sufficient permissions to access snapshot and reference files.
   * This means that to run mapreduce over snapshot files, the MR job has to be run as the HBase
   * user or the user must have group or other privileges in the filesystem (See HBASE-8369).
   * Note that, given other users access to read from snapshot/data files will completely circumvent
   * the access control enforced by HBase.
   * @see org.apache.hadoop.hbase.client.TableSnapshotScanner
   */
  @InterfaceAudience.Public
  @InterfaceStability.Evolving
  public class TableSnapshotInputFormat extends InputFormat<ImmutableBytesWritable, Result> {
  
    public static class TableSnapshotRegionSplit extends InputSplit implements Writable {
      private TableSnapshotInputFormatImpl.InputSplit delegate;
  
      // constructor for mapreduce framework / Writable
      public TableSnapshotRegionSplit() {
        this.delegate = new TableSnapshotInputFormatImpl.InputSplit();
      }
  
      public TableSnapshotRegionSplit(TableSnapshotInputFormatImpl.InputSplit delegate) {
        this.delegate = delegate;
      }
  
     public TableSnapshotRegionSplit(HTableDescriptor htd, HRegionInfo regionInfo,
         List<String> locations) {
       this.delegate = new TableSnapshotInputFormatImpl.InputSplit(htd, regionInfo, locations);
     }
 
     @Override
     public long getLength() throws IOException, InterruptedException {
       return delegate.getLength();
     }
 
     @Override
     public String[] getLocations() throws IOException, InterruptedException {
       return delegate.getLocations();
     }
 
     @Override
     public void write(DataOutput out) throws IOException {
       delegate.write(out);
     }
 
     @Override
     public void readFields(DataInput in) throws IOException {
       delegate.readFields(in);
     }
   }
 
   @VisibleForTesting
   static class TableSnapshotRegionRecordReader extends
       RecordReader<ImmutableBytesWritable, Result> {
     private TableSnapshotInputFormatImpl.RecordReader delegate =
       new TableSnapshotInputFormatImpl.RecordReader();
     private TaskAttemptContext context;
     private Method getCounter;
 
     @Override
     public void initialize(InputSplit split, TaskAttemptContext context) throws IOException,
         InterruptedException {
       this.context = context;
       getCounter = TableRecordReaderImpl.retrieveGetCounterWithStringsParams(context);
       delegate.initialize(
         ((TableSnapshotRegionSplit) split).delegate,
         context.getConfiguration());
     }
 
     @Override
     public boolean nextKeyValue() throws IOException, InterruptedException {
       boolean result = delegate.nextKeyValue();
       if (result) {
         ScanMetrics scanMetrics = delegate.getScanner().getScanMetrics();
         if (scanMetrics != null && context != null) {
           TableRecordReaderImpl.updateCounters(scanMetrics, 0, getCounter, context, 0);
         }
       }
       return result;
     }
 
     @Override
     public ImmutableBytesWritable getCurrentKey() throws IOException, InterruptedException {
       return delegate.getCurrentKey();
     }
 
     @Override
     public Result getCurrentValue() throws IOException, InterruptedException {
       return delegate.getCurrentValue();
     }
 
     @Override
     public float getProgress() throws IOException, InterruptedException {
       return delegate.getProgress();
     }
 
     @Override
     public void close() throws IOException {
       delegate.close();
     }
   }
 
   @Override
   public RecordReader<ImmutableBytesWritable, Result> createRecordReader(
       InputSplit split, TaskAttemptContext context) throws IOException {
     return new TableSnapshotRegionRecordReader();
   }
 
   @Override
   public List<InputSplit> getSplits(JobContext job) throws IOException, InterruptedException {
     List<InputSplit> results = new ArrayList<InputSplit>();
     for (TableSnapshotInputFormatImpl.InputSplit split :
         TableSnapshotInputFormatImpl.getSplits(job.getConfiguration())) {
       results.add(new TableSnapshotRegionSplit(split));
     }
     return results;
   }
 
   /**
    * Configures the job to use TableSnapshotInputFormat to read from a snapshot.
    * @param job the job to configure
    * @param snapshotName the name of the snapshot to read from
    * @param restoreDir a temporary directory to restore the snapshot into. Current user should
    * have write permissions to this directory, and this should not be a subdirectory of rootdir.
    * After the job is finished, restoreDir can be deleted.
    * @throws IOException if an error occurs
    */
   public static void setInput(Job job, String snapshotName, Path restoreDir)
       throws IOException {
     TableSnapshotInputFormatImpl.setInput(job.getConfiguration(), snapshotName, restoreDir);
   }
 }