/*
    * 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.omid.transaction;
  
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.KeyValueUtil;
  import org.apache.hadoop.hbase.filter.Filter;
  import org.apache.omid.OmidFilterBase;
  
  import java.io.IOException;
  import java.util.List;
  
  /**
   * {@link Filter} that encapsulates another {@link Filter}. It remembers the last {@link KeyValue}
   * for which the underlying filter returned the {@link ReturnCode#NEXT_COL} or {@link ReturnCode#INCLUDE_AND_NEXT_COL},
   * so that when {@link #filterKeyValue} is called again for the same {@link KeyValue} with different
   * version, it returns {@link ReturnCode#NEXT_COL} directly without consulting the underlying {@link Filter}.
   * Please see TEPHRA-169 for more details.
   */
  
  public class CellSkipFilterBase extends OmidFilterBase {
      private final Filter filter;
      // remember the previous keyvalue processed by filter when the return code was NEXT_COL or INCLUDE_AND_NEXT_COL
      private KeyValue skipColumn = null;
  
      public CellSkipFilterBase(Filter filter) {
          this.filter = filter;
      }
  
      /**
       * Determines whether the current cell should be skipped. The cell will be skipped
       * if the previous keyvalue had the same key as the current cell. This means filter already responded
       * for the previous keyvalue with ReturnCode.NEXT_COL or ReturnCode.INCLUDE_AND_NEXT_COL.
       * @param cell the {@link Cell} to be tested for skipping
       * @return true is current cell should be skipped, false otherwise
       */
      private boolean skipCellVersion(Cell cell) {
          return skipColumn != null
          && CellUtil.matchingRow(cell, skipColumn.getRowArray(), skipColumn.getRowOffset(),
                  skipColumn.getRowLength())
                  && CellUtil.matchingFamily(cell, skipColumn.getFamilyArray(), skipColumn.getFamilyOffset(),
                  skipColumn.getFamilyLength())
                  && CellUtil.matchingQualifier(cell, skipColumn.getQualifierArray(), skipColumn.getQualifierOffset(),
                  skipColumn.getQualifierLength());
      }
  
      @Override
      public ReturnCode filterKeyValue(Cell cell) throws IOException {
          if (skipCellVersion(cell)) {
              return ReturnCode.NEXT_COL;
          }
  
          ReturnCode code = filter.filterKeyValue(cell);
          if (code == ReturnCode.NEXT_COL || code == ReturnCode.INCLUDE_AND_NEXT_COL) {
              // only store the reference to the keyvalue if we are returning NEXT_COL or INCLUDE_AND_NEXT_COL
              skipColumn = KeyValueUtil.createFirstOnRow(cell.getRowArray(), cell.getRowOffset(), cell.getRowLength(),
                      cell.getFamilyArray(), cell.getFamilyOffset(),
                      cell.getFamilyLength(), cell.getQualifierArray(),
                      cell.getQualifierOffset(), cell.getQualifierLength());
          } else {
              skipColumn = null;
          }
          return code;
      }
  
      @Override
      public boolean filterRow() throws IOException {
          return filter.filterRow();
      }
  
      @Override
      public Cell transformCell(Cell cell) throws IOException {
          return filter.transformCell(cell);
      }
  
      @Override
      public void reset() throws IOException {
          filter.reset();
      }
  
      @Override
      public boolean filterRowKey(byte[] buffer, int offset, int length) throws IOException {
         return filter.filterRowKey(buffer, offset, length);
     }
 
     @Override
     public boolean filterAllRemaining() throws IOException {
         return filter.filterAllRemaining();
     }
 
     @Override
     public void filterRowCells(List<Cell> kvs) throws IOException {
         filter.filterRowCells(kvs);
     }
 
     @Override
     public boolean hasFilterRow() {
         return filter.hasFilterRow();
     }
 
     @Override
     public Cell getNextCellHint(Cell currentKV) throws IOException {
         return filter.getNextCellHint(currentKV);
     }
 
     @Override
     public boolean isFamilyEssential(byte[] name) throws IOException {
         return filter.isFamilyEssential(name);
     }
 
     @Override
     public byte[] toByteArray() throws IOException {
         return filter.toByteArray();
     }
 
     public Filter getInnerFilter() {
         return filter;
     }
 }