/*
    * 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 com.google.common.annotations.VisibleForTesting;
  import com.google.common.base.Optional;
  import com.google.common.collect.Iterators;
  import com.google.common.collect.PeekingIterator;
  import org.apache.omid.HBaseShims;
  import org.apache.omid.committable.CommitTable;
  import org.apache.omid.committable.CommitTable.Client;
  import org.apache.omid.committable.CommitTable.CommitTimestamp;
  import org.apache.omid.transaction.CellUtils;
  import org.apache.omid.transaction.CellInfo;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.client.Get;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.coprocessor.ObserverContext;
  import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Queue;
  import java.util.SortedMap;
  import java.util.concurrent.ExecutionException;
  
  import static org.apache.omid.committable.CommitTable.CommitTimestamp.Location.SHADOW_CELL;
  
  public class CompactorScanner implements InternalScanner {
      private static final Logger LOG = LoggerFactory.getLogger(CompactorScanner.class);
      private final InternalScanner internalScanner;
      private final CommitTable.Client commitTableClient;
      private final Queue<CommitTable.Client> commitTableClientQueue;
      private final boolean isMajorCompaction;
      private final boolean retainNonTransactionallyDeletedCells;
      private final long lowWatermark;
  
      private final Region hRegion;
  
      private boolean hasMoreRows = false;
      private List<Cell> currentRowWorthValues = new ArrayList<Cell>();
  
      public CompactorScanner(ObserverContext<RegionCoprocessorEnvironment> e,
                              InternalScanner internalScanner,
                              Client commitTableClient,
                              Queue<CommitTable.Client> commitTableClientQueue,
                              boolean isMajorCompaction,
                              boolean preserveNonTransactionallyDeletedCells) throws IOException {
          this.internalScanner = internalScanner;
          this.commitTableClient = commitTableClient;
          this.commitTableClientQueue = commitTableClientQueue;
          this.isMajorCompaction = isMajorCompaction;
          this.retainNonTransactionallyDeletedCells = preserveNonTransactionallyDeletedCells;
          this.lowWatermark = getLowWatermarkFromCommitTable();
          // Obtain the table in which the scanner is going to operate
          this.hRegion = HBaseShims.getRegionCoprocessorRegion(e.getEnvironment());
          LOG.info("Scanner cleaning up uncommitted txs older than LW [{}] in region [{}]",
                  lowWatermark, hRegion.getRegionInfo());
      }
  
      @Override
      public boolean next(List<Cell> results) throws IOException {
          return next(results, -1);
      }
  
      public boolean next(List<Cell> result, ScannerContext scannerContext) throws IOException {
          int limit = scannerContext.getBatchLimit();
          return next(result, limit);
      }
  
      public boolean next(List<Cell> result, int limit) throws IOException {
  
          if (currentRowWorthValues.isEmpty()) {
              // 1) Read next row
              List<Cell> scanResult = new ArrayList<Cell>();
             hasMoreRows = internalScanner.next(scanResult);
             if (LOG.isTraceEnabled()) {
                 LOG.trace("Row: Result {} limit {} more rows? {}", scanResult, limit, hasMoreRows);
             }
             // 2) Traverse result list separating normal cells from shadow
             // cells and building a map to access easily the shadow cells.
             SortedMap<Cell, Optional<Cell>> cellToSc = CellUtils.mapCellsToShadowCells(scanResult);
 
             // 3) traverse the list of row key values isolated before and
             // check which ones should be discarded
             Map<String, CellInfo> lastTimestampedCellsInRow = new HashMap<>();
             PeekingIterator<Map.Entry<Cell, Optional<Cell>>> iter
                     = Iterators.peekingIterator(cellToSc.entrySet().iterator());
             while (iter.hasNext()) {
                 Map.Entry<Cell, Optional<Cell>> entry = iter.next();
                 Cell cell = entry.getKey();
                 Optional<Cell> shadowCellOp = entry.getValue();
 
                 if (cell.getTimestamp() > lowWatermark) {
                     retain(currentRowWorthValues, cell, shadowCellOp);
                     continue;
                 }
 
                 if (shouldRetainNonTransactionallyDeletedCell(cell)) {
                     retain(currentRowWorthValues, cell, shadowCellOp);
                     continue;
                 }
 
                 // During a minor compaction the coprocessor may only see a
                 // subset of store files and may not have the all the versions
                 // of a cell available for consideration. Therefore, if it
                 // deletes a cell with a tombstone during a minor compaction,
                 // an older version of the cell may become visible again. So,
                 // we have to remove tombstones only in major compactions.
                 if (isMajorCompaction) {
                     if (CellUtils.isTombstone(cell)) {
                         if (shadowCellOp.isPresent()) {
                             skipToNextColumn(cell, iter);
                         } else {
                             Optional<CommitTimestamp> commitTimestamp = queryCommitTimestamp(cell);
                             // Clean the cell only if it is valid
                             if (commitTimestamp.isPresent() && commitTimestamp.get().isValid()) {
                                 skipToNextColumn(cell, iter);
                             }
                         }
                         continue;
                     }
                 }
 
                 if (shadowCellOp.isPresent()) {
                     saveLastTimestampedCell(lastTimestampedCellsInRow, cell, shadowCellOp.get());
                 } else {
                     Optional<CommitTimestamp> commitTimestamp = queryCommitTimestamp(cell);
                     if (commitTimestamp.isPresent() && commitTimestamp.get().isValid()) {
                         // Build the missing shadow cell...
                         byte[] shadowCellValue = Bytes.toBytes(commitTimestamp.get().getValue());
                         Cell shadowCell = CellUtils.buildShadowCellFromCell(cell, shadowCellValue);
                         saveLastTimestampedCell(lastTimestampedCellsInRow, cell, shadowCell);
                     } else {
                         LOG.trace("Discarding cell {}", cell);
                     }
                 }
             }
             retainLastTimestampedCellsSaved(currentRowWorthValues, lastTimestampedCellsInRow);
 
             // 4) Sort the list
             Collections.sort(currentRowWorthValues, KeyValue.COMPARATOR);
         }
 
         // Chomp current row worth values up to the limit
         if (currentRowWorthValues.size() <= limit) {
             result.addAll(currentRowWorthValues);
             currentRowWorthValues.clear();
         } else {
             result.addAll(currentRowWorthValues.subList(0, limit));
             currentRowWorthValues.subList(0, limit).clear();
         }
         LOG.trace("Results to preserve {}", result);
 
         return hasMoreRows;
     }
 
     @Override
     public void close() throws IOException {
         internalScanner.close();
         commitTableClientQueue.add(commitTableClient);
     }
 
     // ----------------------------------------------------------------------------------------------------------------
     // Helper methods
     // ----------------------------------------------------------------------------------------------------------------
 
     @VisibleForTesting
     public boolean shouldRetainNonTransactionallyDeletedCell(Cell cell) {
         return (CellUtil.isDelete(cell) || CellUtil.isDeleteFamily(cell))
                 &&
                 retainNonTransactionallyDeletedCells;
     }
 
     private void saveLastTimestampedCell(Map<String, CellInfo> lastCells, Cell cell, Cell shadowCell) {
         String cellKey = Bytes.toString(cell.getFamilyArray(), cell.getFamilyOffset(), cell.getFamilyLength())
                 + ":"
                 + Bytes.toString(cell.getQualifierArray(), cell.getQualifierOffset(), cell.getQualifierLength());
         LOG.trace("Cell Key: {}", cellKey);
 
         if (!lastCells.containsKey(cellKey)) {
             lastCells.put(cellKey, new CellInfo(cell, shadowCell));
         } else {
             if (lastCells.get(cellKey).getTimestamp() < cell.getTimestamp()) {
                 lastCells.put(cellKey, new CellInfo(cell, shadowCell));
             } else {
                 LOG.trace("Forgetting old cell {}", cell);
             }
         }
     }
 
     private long getLowWatermarkFromCommitTable() throws IOException {
         try {
             LOG.trace("About to read log watermark from commit table");
             return commitTableClient.readLowWatermark().get();
         } catch (InterruptedException ie) {
             Thread.currentThread().interrupt();
             LOG.warn("Interrupted getting low watermark from commit table", ie);
             throw new IOException("Interrupted getting low watermark from commit table");
         } catch (ExecutionException ee) {
             LOG.warn("Problem getting low watermark from commit table");
             throw new IOException("Problem getting low watermark from commit table", ee.getCause());
         }
     }
 
     private Optional<CommitTimestamp> queryCommitTimestamp(Cell cell) throws IOException {
         try {
             Optional<CommitTimestamp> ct = commitTableClient.getCommitTimestamp(cell.getTimestamp()).get();
             if (ct.isPresent()) {
                 return Optional.of(ct.get());
             } else {
                 Get g = new Get(CellUtil.cloneRow(cell));
                 byte[] family = CellUtil.cloneFamily(cell);
                 byte[] qualifier = CellUtils.addShadowCellSuffixPrefix(cell.getQualifierArray(),
                         cell.getQualifierOffset(),
                         cell.getQualifierLength());
                 g.addColumn(family, qualifier);
                 g.setTimeStamp(cell.getTimestamp());
                 Result r = hRegion.get(g);
                 if (r.containsColumn(family, qualifier)) {
                     return Optional.of(new CommitTimestamp(SHADOW_CELL,
                             Bytes.toLong(r.getValue(family, qualifier)), true));
                 }
             }
         } catch (InterruptedException e) {
             Thread.currentThread().interrupt();
             throw new IOException("Interrupted while getting commit timestamp from commit table");
         } catch (ExecutionException e) {
             throw new IOException("Error getting commit timestamp from commit table", e);
         }
 
         return Optional.absent();
     }
 
     private void retain(List<Cell> result, Cell cell, Optional<Cell> shadowCell) {
         LOG.trace("Retaining cell {}", cell);
         result.add(cell);
         if (shadowCell.isPresent()) {
             LOG.trace("...with shadow cell {}", cell, shadowCell.get());
             result.add(shadowCell.get());
         } else {
             LOG.trace("...without shadow cell! (TS is above Low Watermark)");
         }
     }
 
     private void retainLastTimestampedCellsSaved(List<Cell> result, Map<String, CellInfo> lastTimestampedCellsInRow) {
         for (CellInfo cellInfo : lastTimestampedCellsInRow.values()) {
             LOG.trace("Retaining last cell {} with shadow cell {}", cellInfo.getCell(), cellInfo.getShadowCell());
             result.add(cellInfo.getCell());
             result.add(cellInfo.getShadowCell());
         }
     }
 
     private void skipToNextColumn(Cell cell, PeekingIterator<Map.Entry<Cell, Optional<Cell>>> iter) {
         while (iter.hasNext()
                 && CellUtil.matchingFamily(iter.peek().getKey(), cell)
                 && CellUtil.matchingQualifier(iter.peek().getKey(), cell)) {
             iter.next();
         }
     }
 
 }