/**
    * 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 org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.HDFSBlocksDistribution;
  import org.apache.hadoop.hbase.HDFSBlocksDistribution.HostAndWeight;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.client.ClientSideRegionScanner;
  import org.apache.hadoop.hbase.client.IsolationLevel;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.SnapshotDescription;
  import org.apache.hadoop.hbase.protobuf.generated.MapReduceProtos.TableSnapshotRegionSplit;
  import org.apache.hadoop.hbase.protobuf.generated.SnapshotProtos.SnapshotRegionManifest;
  import org.apache.hadoop.hbase.regionserver.HRegion;
  import org.apache.hadoop.hbase.snapshot.RestoreSnapshotHelper;
  import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;
  import org.apache.hadoop.hbase.snapshot.SnapshotManifest;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.FSUtils;
  import org.apache.hadoop.io.Writable;
  
  import java.io.ByteArrayOutputStream;
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.UUID;
  
  /**
   * Hadoop MR API-agnostic implementation for mapreduce over table snapshots.
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public class TableSnapshotInputFormatImpl {
    // TODO: Snapshots files are owned in fs by the hbase user. There is no
    // easy way to delegate access.
  
    private static final String SNAPSHOT_NAME_KEY = "hbase.TableSnapshotInputFormat.snapshot.name";
    // key for specifying the root dir of the restored snapshot
    private static final String RESTORE_DIR_KEY = "hbase.TableSnapshotInputFormat.restore.dir";
  
    /** See {@link #getBestLocations(Configuration, HDFSBlocksDistribution)} */
    private static final String LOCALITY_CUTOFF_MULTIPLIER =
      "hbase.tablesnapshotinputformat.locality.cutoff.multiplier";
    private static final float DEFAULT_LOCALITY_CUTOFF_MULTIPLIER = 0.8f;
  
    /**
     * Implementation class for InputSplit logic common between mapred and mapreduce.
     */
    public static class InputSplit implements Writable {
      private HTableDescriptor htd;
      private HRegionInfo regionInfo;
      private String[] locations;
  
      // constructor for mapreduce framework / Writable
      public InputSplit() {}
  
      public InputSplit(HTableDescriptor htd, HRegionInfo regionInfo, List<String> locations) {
        this.htd = htd;
        this.regionInfo = regionInfo;
        if (locations == null || locations.isEmpty()) {
          this.locations = new String[0];
        } else {
          this.locations = locations.toArray(new String[locations.size()]);
        }
      }
  
      public long getLength() {
        //TODO: We can obtain the file sizes of the snapshot here.
        return 0;
      }
  
      public String[] getLocations() {
       return locations;
     }
 
     public HTableDescriptor getTableDescriptor() {
       return htd;
     }
 
     public HRegionInfo getRegionInfo() {
       return regionInfo;
     }
 
     // TODO: We should have ProtobufSerialization in Hadoop, and directly use PB objects instead of
     // doing this wrapping with Writables.
     @Override
     public void write(DataOutput out) throws IOException {
       TableSnapshotRegionSplit.Builder builder = TableSnapshotRegionSplit.newBuilder()
           .setTable(htd.convert())
           .setRegion(HRegionInfo.convert(regionInfo));
 
       for (String location : locations) {
         builder.addLocations(location);
       }
 
       TableSnapshotRegionSplit split = builder.build();
 
       ByteArrayOutputStream baos = new ByteArrayOutputStream();
       split.writeTo(baos);
       baos.close();
       byte[] buf = baos.toByteArray();
       out.writeInt(buf.length);
       out.write(buf);
     }
 
     @Override
     public void readFields(DataInput in) throws IOException {
       int len = in.readInt();
       byte[] buf = new byte[len];
       in.readFully(buf);
       TableSnapshotRegionSplit split = TableSnapshotRegionSplit.PARSER.parseFrom(buf);
       this.htd = HTableDescriptor.convert(split.getTable());
       this.regionInfo = HRegionInfo.convert(split.getRegion());
       List<String> locationsList = split.getLocationsList();
       this.locations = locationsList.toArray(new String[locationsList.size()]);
     }
   }
 
   /**
    * Implementation class for RecordReader logic common between mapred and mapreduce.
    */
   public static class RecordReader {
     private InputSplit split;
     private Scan scan;
     private Result result = null;
     private ImmutableBytesWritable row = null;
     private ClientSideRegionScanner scanner;
 
     public ClientSideRegionScanner getScanner() {
       return scanner;
     }
 
     public void initialize(InputSplit split, Configuration conf) throws IOException {
       this.split = split;
       HTableDescriptor htd = split.htd;
       HRegionInfo hri = this.split.getRegionInfo();
       FileSystem fs = FSUtils.getCurrentFileSystem(conf);
 
       Path tmpRootDir = new Path(conf.get(RESTORE_DIR_KEY)); // This is the user specified root
       // directory where snapshot was restored
 
       // create scan
       // TODO: mapred does not support scan as input API. Work around for now.
       if (conf.get(TableInputFormat.SCAN) != null) {
         scan = TableMapReduceUtil.convertStringToScan(conf.get(TableInputFormat.SCAN));
       } else if (conf.get(org.apache.hadoop.hbase.mapred.TableInputFormat.COLUMN_LIST) != null) {
         String[] columns =
           conf.get(org.apache.hadoop.hbase.mapred.TableInputFormat.COLUMN_LIST).split(" ");
         scan = new Scan();
         for (String col : columns) {
           scan.addFamily(Bytes.toBytes(col));
         }
       } else {
         throw new IllegalArgumentException("A Scan is not configured for this job");
       }
 
       // region is immutable, this should be fine,
       // otherwise we have to set the thread read point
       scan.setIsolationLevel(IsolationLevel.READ_UNCOMMITTED);
       // disable caching of data blocks
       scan.setCacheBlocks(false);
 
       scanner = new ClientSideRegionScanner(conf, fs, tmpRootDir, htd, hri, scan, null);
     }
 
     public boolean nextKeyValue() throws IOException {
       result = scanner.next();
       if (result == null) {
         //we are done
         return false;
       }
 
       if (this.row == null) {
         this.row = new ImmutableBytesWritable();
       }
       this.row.set(result.getRow());
       return true;
     }
 
     public ImmutableBytesWritable getCurrentKey() {
       return row;
     }
 
     public Result getCurrentValue() {
       return result;
     }
 
     public long getPos() {
       return 0;
     }
 
     public float getProgress() {
       return 0; // TODO: use total bytes to estimate
     }
 
     public void close() {
       if (this.scanner != null) {
         this.scanner.close();
       }
     }
   }
 
   public static List<InputSplit> getSplits(Configuration conf) throws IOException {
     String snapshotName = getSnapshotName(conf);
 
     Path rootDir = FSUtils.getRootDir(conf);
     FileSystem fs = rootDir.getFileSystem(conf);
 
     Path snapshotDir = SnapshotDescriptionUtils.getCompletedSnapshotDir(snapshotName, rootDir);
     SnapshotDescription snapshotDesc = SnapshotDescriptionUtils.readSnapshotInfo(fs, snapshotDir);
     SnapshotManifest manifest = SnapshotManifest.open(conf, fs, snapshotDir, snapshotDesc);
     List<SnapshotRegionManifest> regionManifests = manifest.getRegionManifests();
     if (regionManifests == null) {
       throw new IllegalArgumentException("Snapshot seems empty");
     }
 
     // load table descriptor
     HTableDescriptor htd = manifest.getTableDescriptor();
 
     // TODO: mapred does not support scan as input API. Work around for now.
     Scan scan = null;
     if (conf.get(TableInputFormat.SCAN) != null) {
       scan = TableMapReduceUtil.convertStringToScan(conf.get(TableInputFormat.SCAN));
     } else if (conf.get(org.apache.hadoop.hbase.mapred.TableInputFormat.COLUMN_LIST) != null) {
       String[] columns =
         conf.get(org.apache.hadoop.hbase.mapred.TableInputFormat.COLUMN_LIST).split(" ");
       scan = new Scan();
       for (String col : columns) {
         scan.addFamily(Bytes.toBytes(col));
       }
     } else {
       throw new IllegalArgumentException("Unable to create scan");
     }
     // the temp dir where the snapshot is restored
     Path restoreDir = new Path(conf.get(RESTORE_DIR_KEY));
     Path tableDir = FSUtils.getTableDir(restoreDir, htd.getTableName());
 
     List<InputSplit> splits = new ArrayList<InputSplit>();
     for (SnapshotRegionManifest regionManifest : regionManifests) {
       // load region descriptor
       HRegionInfo hri = HRegionInfo.convert(regionManifest.getRegionInfo());
 
       if (CellUtil.overlappingKeys(scan.getStartRow(), scan.getStopRow(),
         hri.getStartKey(), hri.getEndKey())) {
         // compute HDFS locations from snapshot files (which will get the locations for
         // referred hfiles)
         List<String> hosts = getBestLocations(conf,
           HRegion.computeHDFSBlocksDistribution(conf, htd, hri, tableDir));
 
         int len = Math.min(3, hosts.size());
         hosts = hosts.subList(0, len);
         splits.add(new InputSplit(htd, hri, hosts));
       }
     }
 
     return splits;
   }
 
   /**
    * This computes the locations to be passed from the InputSplit. MR/Yarn schedulers does not take
    * weights into account, thus will treat every location passed from the input split as equal. We
    * do not want to blindly pass all the locations, since we are creating one split per region, and
    * the region's blocks are all distributed throughout the cluster unless favorite node assignment
    * is used. On the expected stable case, only one location will contain most of the blocks as
    * local.
    * On the other hand, in favored node assignment, 3 nodes will contain highly local blocks. Here
    * we are doing a simple heuristic, where we will pass all hosts which have at least 80%
    * (hbase.tablesnapshotinputformat.locality.cutoff.multiplier) as much block locality as the top
    * host with the best locality.
    */
   public static List<String> getBestLocations(
       Configuration conf, HDFSBlocksDistribution blockDistribution) {
     List<String> locations = new ArrayList<String>(3);
 
     HostAndWeight[] hostAndWeights = blockDistribution.getTopHostsWithWeights();
 
     if (hostAndWeights.length == 0) {
       return locations;
     }
 
     HostAndWeight topHost = hostAndWeights[0];
     locations.add(topHost.getHost());
 
     // Heuristic: filter all hosts which have at least cutoffMultiplier % of block locality
     double cutoffMultiplier
       = conf.getFloat(LOCALITY_CUTOFF_MULTIPLIER, DEFAULT_LOCALITY_CUTOFF_MULTIPLIER);
 
     double filterWeight = topHost.getWeight() * cutoffMultiplier;
 
     for (int i = 1; i < hostAndWeights.length; i++) {
       if (hostAndWeights[i].getWeight() >= filterWeight) {
         locations.add(hostAndWeights[i].getHost());
       } else {
         break;
       }
     }
 
     return locations;
   }
 
   private static String getSnapshotName(Configuration conf) {
     String snapshotName = conf.get(SNAPSHOT_NAME_KEY);
     if (snapshotName == null) {
       throw new IllegalArgumentException("Snapshot name must be provided");
     }
     return snapshotName;
   }
 
   /**
    * Configures the job to use TableSnapshotInputFormat to read from a snapshot.
    * @param conf the job to configuration
    * @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(Configuration conf, String snapshotName, Path restoreDir)
       throws IOException {
     conf.set(SNAPSHOT_NAME_KEY, snapshotName);
 
     Path rootDir = FSUtils.getRootDir(conf);
     FileSystem fs = rootDir.getFileSystem(conf);
 
     restoreDir = new Path(restoreDir, UUID.randomUUID().toString());
 
     // TODO: restore from record readers to parallelize.
     RestoreSnapshotHelper.copySnapshotForScanner(conf, fs, rootDir, restoreDir, snapshotName);
 
     conf.set(RESTORE_DIR_KEY, restoreDir.toString());
   }
 }