/*
    * 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.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.monitoring.MonitoredTask;
  import org.apache.hadoop.hbase.regionserver.compactions.Compactor;
  
  /**
   * Store flusher interface. Turns a snapshot of memstore into a set of store files (usually one).
   * Custom implementation can be provided.
   */
  @InterfaceAudience.Private
  abstract class StoreFlusher {
    protected Configuration conf;
    protected Store store;
  
    public StoreFlusher(Configuration conf, Store store) {
      this.conf = conf;
      this.store = store;
    }
  
    /**
     * Turns a snapshot of memstore into a set of store files.
     * @param snapshot Memstore snapshot.
     * @param cacheFlushSeqNum Log cache flush sequence number.
     * @param status Task that represents the flush operation and may be updated with status.
     * @return List of files written. Can be empty; must not be null.
     */
    public abstract List<Path> flushSnapshot(MemStoreSnapshot snapshot, long cacheFlushSeqNum,
        MonitoredTask status) throws IOException;
  
    protected void finalizeWriter(StoreFile.Writer writer, long cacheFlushSeqNum,
        MonitoredTask status) throws IOException {
      // Write out the log sequence number that corresponds to this output
      // hfile. Also write current time in metadata as minFlushTime.
      // The hfile is current up to and including cacheFlushSeqNum.
      status.setStatus("Flushing " + store + ": appending metadata");
      writer.appendMetadata(cacheFlushSeqNum, false);
      status.setStatus("Flushing " + store + ": closing flushed file");
      writer.close();
    }
  
  
    /**
     * Creates the scanner for flushing snapshot. Also calls coprocessors.
     * @param snapshotScanner
     * @param smallestReadPoint
     * @return The scanner; null if coprocessor is canceling the flush.
     */
    protected InternalScanner createScanner(KeyValueScanner snapshotScanner,
        long smallestReadPoint) throws IOException {
      InternalScanner scanner = null;
      if (store.getCoprocessorHost() != null) {
        scanner = store.getCoprocessorHost().preFlushScannerOpen(store, snapshotScanner);
      }
      if (scanner == null) {
        Scan scan = new Scan();
        scan.setMaxVersions(store.getScanInfo().getMaxVersions());
        scanner = new StoreScanner(store, store.getScanInfo(), scan,
            Collections.singletonList(snapshotScanner), ScanType.COMPACT_RETAIN_DELETES,
            smallestReadPoint, HConstants.OLDEST_TIMESTAMP);
      }
      assert scanner != null;
      if (store.getCoprocessorHost() != null) {
        try {
          return store.getCoprocessorHost().preFlush(store, scanner);
        } catch (IOException ioe) {
          scanner.close();
          throw ioe;
        }
      }
      return scanner;
   }
 
   /**
    * Performs memstore flush, writing data from scanner into sink.
    * @param scanner Scanner to get data from.
    * @param sink Sink to write data to. Could be StoreFile.Writer.
    * @param smallestReadPoint Smallest read point used for the flush.
    */
   protected void performFlush(InternalScanner scanner,
       Compactor.CellSink sink, long smallestReadPoint) throws IOException {
     int compactionKVMax =
       conf.getInt(HConstants.COMPACTION_KV_MAX, HConstants.COMPACTION_KV_MAX_DEFAULT);
 
     ScannerContext scannerContext =
         ScannerContext.newBuilder().setBatchLimit(compactionKVMax).build();
 
     List<Cell> kvs = new ArrayList<Cell>();
     boolean hasMore;
     do {
       hasMore = scanner.next(kvs, scannerContext);
       if (!kvs.isEmpty()) {
         for (Cell c : kvs) {
           // If we know that this KV is going to be included always, then let us
           // set its memstoreTS to 0. This will help us save space when writing to
           // disk.
           sink.append(c);
         }
         kvs.clear();
       }
     } while (hasMore);
   }
 }