/**
    * 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.client;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
  import org.apache.hadoop.hbase.regionserver.HRegion;
  import org.apache.hadoop.hbase.regionserver.RegionScanner;
  
  /**
   * A client scanner for a region opened for read-only on the client side. Assumes region data
   * is not changing.
   */
  @InterfaceAudience.Private
  public class ClientSideRegionScanner extends AbstractClientScanner {
  
    private static final Log LOG = LogFactory.getLog(ClientSideRegionScanner.class);
  
    private HRegion region;
    RegionScanner scanner;
    List<Cell> values;
  
    public ClientSideRegionScanner(Configuration conf, FileSystem fs,
        Path rootDir, HTableDescriptor htd, HRegionInfo hri, Scan scan, ScanMetrics scanMetrics)
            throws IOException {
      // region is immutable, set isolation level
      scan.setIsolationLevel(IsolationLevel.READ_UNCOMMITTED);
  
      htd.setReadOnly(true);
  
      // open region from the snapshot directory
      this.region = HRegion.openHRegion(conf, fs, rootDir, hri, htd, null, null, null);
  
      // create an internal region scanner
      this.scanner = region.getScanner(scan);
      values = new ArrayList<Cell>();
  
      if (scanMetrics == null) {
        initScanMetrics(scan);
      } else {
        this.scanMetrics = scanMetrics;
      }
      region.startRegionOperation();
    }
  
    @Override
    public Result next() throws IOException {
      values.clear();
      scanner.nextRaw(values);
      if (values.isEmpty()) {
        //we are done
        return null;
      }
  
      Result result = Result.create(values);
      if (this.scanMetrics != null) {
        long resultSize = 0;
        for (Cell cell : values) {
          resultSize += CellUtil.estimatedSerializedSizeOf(cell);
        }
        this.scanMetrics.countOfBytesInResults.addAndGet(resultSize);
        this.scanMetrics.countOfRowsScanned.incrementAndGet();
      }
  
      return result;
    }
  
    @Override
    public void close() {
      if (this.scanner != null) {
       try {
         this.scanner.close();
         this.scanner = null;
       } catch (IOException ex) {
         LOG.warn("Exception while closing scanner", ex);
       }
     }
     if (this.region != null) {
       try {
         this.region.closeRegionOperation();
         this.region.close(true);
         this.region = null;
       } catch (IOException ex) {
         LOG.warn("Exception while closing region", ex);
       }
     }
   }
 
   @Override
   public boolean renewLease() {
     throw new UnsupportedOperationException();
   }
 }