/**
    * Copyright The Apache Software Foundation
    *
    * 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.regionserver;
  
  import java.io.IOException;
  import java.util.List;
  
  import org.apache.hadoop.hbase.KeyValueUtil;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.regionserver.HRegion.RegionScannerImpl;
  
  /**
   * ReversibleRegionScannerImpl extends from RegionScannerImpl, and is used to
   * support reversed scanning.
   */
  @InterfaceAudience.Private
  class ReversedRegionScannerImpl extends RegionScannerImpl {
  
    /**
     * @param scan
     * @param additionalScanners
     * @param region
     * @throws IOException
     */
    ReversedRegionScannerImpl(Scan scan,
        List<KeyValueScanner> additionalScanners, HRegion region)
        throws IOException {
      region.super(scan, additionalScanners, region);
    }
  
    @Override
    protected void initializeKVHeap(List<KeyValueScanner> scanners,
        List<KeyValueScanner> joinedScanners, HRegion region) throws IOException {
      this.storeHeap = new ReversedKeyValueHeap(scanners, region.getComparator());
      if (!joinedScanners.isEmpty()) {
        this.joinedHeap = new ReversedKeyValueHeap(joinedScanners,
            region.getComparator());
      }
    }
  
    @Override
    protected boolean isStopRow(byte[] currentRow, int offset, short length) {
      return currentRow == null
          || (super.stopRow != null && region.getComparator().compareRows(
              stopRow, 0, stopRow.length, currentRow, offset, length) >= super.isScan);
    }
  
    @Override
    protected boolean nextRow(ScannerContext scannerContext, byte[] currentRow, int offset,
        short length) throws IOException {
      assert super.joinedContinuationRow == null : "Trying to go to next row during joinedHeap read.";
      byte row[] = new byte[length];
      System.arraycopy(currentRow, offset, row, 0, length);
      this.storeHeap.seekToPreviousRow(KeyValueUtil.createFirstOnRow(row));
      resetFilters();
  
      // Calling the hook in CP which allows it to do a fast forward
      if (this.region.getCoprocessorHost() != null) {
        return this.region.getCoprocessorHost().postScannerFilterRow(this,
            currentRow, offset, length);
      }
      return true;
    }
  
  }