/**
    * 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.client;
  
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.client.ClientSmallScanner.SmallScannerCallable;
  import org.apache.hadoop.hbase.client.ClientSmallScanner.SmallScannerCallableFactory;
  import org.apache.hadoop.hbase.ipc.RpcControllerFactory;
  import org.apache.hadoop.hbase.util.Bytes;
  
  import com.google.common.annotations.VisibleForTesting;
  
  import java.io.IOException;
  import java.util.concurrent.ExecutorService;
  
  /**
   * Client scanner for small reversed scan. Generally, only one RPC is called to fetch the
   * scan results, unless the results cross multiple regions or the row count of
   * results exceed the caching.
   * <p/>
   * For small scan, it will get better performance than {@link ReversedClientScanner}
   */
  @InterfaceAudience.Private
  public class ClientSmallReversedScanner extends ReversedClientScanner {
    private static final Log LOG = LogFactory.getLog(ClientSmallReversedScanner.class);
    private ScannerCallableWithReplicas smallScanCallable = null;
    private SmallScannerCallableFactory callableFactory;
  
    /**
     * Create a new ReversibleClientScanner for the specified table. Take note that the passed
     * {@link Scan} 's start row maybe changed changed.
     *
     * @param conf
     *          The {@link Configuration} to use.
     * @param scan
     *          {@link Scan} to use in this scanner
     * @param tableName
     *          The table that we wish to rangeGet
     * @param connection
     *          Connection identifying the cluster
     * @param rpcFactory
     *          Factory used to create the {@link RpcRetryingCaller}
     * @param controllerFactory
     *          Factory used to access RPC payloads
     * @param pool
     *          Threadpool for RPC threads
     * @param primaryOperationTimeout
     *          Call timeout
     * @throws IOException
     *           If the remote call fails
     */
    public ClientSmallReversedScanner(final Configuration conf, final Scan scan,
        final TableName tableName, ClusterConnection connection, RpcRetryingCallerFactory rpcFactory,
        RpcControllerFactory controllerFactory, ExecutorService pool, int primaryOperationTimeout)
        throws IOException {
      this(conf, scan, tableName, connection, rpcFactory, controllerFactory, pool,
          primaryOperationTimeout, new SmallScannerCallableFactory());
    }
  
    /**
     * Create a new ReversibleClientScanner for the specified table. Take note that the passed
     * {@link Scan}'s start row may be changed.
     *
     * @param conf
     *          The {@link Configuration} to use.
     * @param scan
     *          {@link Scan} to use in this scanner
     * @param tableName
     *          The table that we wish to rangeGet
     * @param connection
     *          Connection identifying the cluster
     * @param rpcFactory
     *          Factory used to create the {@link RpcRetryingCaller}
     * @param controllerFactory
    *          Factory used to access RPC payloads
    * @param pool
    *          Threadpool for RPC threads
    * @param primaryOperationTimeout
    *          Call timeout
    * @param callableFactory
    *          Factory used to create the {@link SmallScannerCallable}
    * @throws IOException
    *           If the remote call fails
    */
   @VisibleForTesting
   ClientSmallReversedScanner(final Configuration conf, final Scan scan, final TableName tableName,
       ClusterConnection connection, RpcRetryingCallerFactory rpcFactory,
       RpcControllerFactory controllerFactory, ExecutorService pool, int primaryOperationTimeout,
       SmallScannerCallableFactory callableFactory) throws IOException {
     super(conf, scan, tableName, connection, rpcFactory, controllerFactory, pool,
         primaryOperationTimeout);
     this.callableFactory = callableFactory;
   }
 
   /**
    * Gets a scanner for following scan. Move to next region or continue from the last result or
    * start from the start row.
    *
    * @param nbRows
    * @param done
    *          true if Server-side says we're done scanning.
    * @param currentRegionDone
    *          true if scan is over on current region
    * @return true if has next scanner
    * @throws IOException
    */
   private boolean nextScanner(int nbRows, final boolean done,
                               boolean currentRegionDone) throws IOException {
     // Where to start the next getter
     byte[] localStartKey;
     int cacheNum = nbRows;
     boolean regionChanged = true;
     // if we're at end of table, close and return false to stop iterating
     if (this.currentRegion != null && currentRegionDone) {
       byte[] startKey = this.currentRegion.getStartKey();
       if (startKey == null
           || Bytes.equals(startKey, HConstants.EMPTY_BYTE_ARRAY)
           || checkScanStopRow(startKey) || done) {
         close();
         if (LOG.isDebugEnabled()) {
           LOG.debug("Finished with small scan at " + this.currentRegion);
         }
         return false;
       }
       // We take the row just under to get to the previous region.
       localStartKey = createClosestRowBefore(startKey);
       if (LOG.isDebugEnabled()) {
         LOG.debug("Finished with region " + this.currentRegion);
       }
     } else if (this.lastResult != null) {
       regionChanged = false;
       localStartKey = createClosestRowBefore(lastResult.getRow());
     } else {
       localStartKey = this.scan.getStartRow();
     }
 
     if (LOG.isTraceEnabled()) {
       LOG.trace("Advancing internal small scanner to startKey at '"
           + Bytes.toStringBinary(localStartKey) + "'");
     }
 
     smallScanCallable = callableFactory.getCallable(getConnection(), getTable(), scan,
         getScanMetrics(), localStartKey, cacheNum, rpcControllerFactory, getPool(),
         getPrimaryOperationTimeout(), getRetries(), getScannerTimeout(), getConf(), caller);
 
     if (this.scanMetrics != null && regionChanged) {
       this.scanMetrics.countOfRegions.incrementAndGet();
     }
     return true;
   }
 
   @Override
   public Result next() throws IOException {
     // If the scanner is closed and there's nothing left in the cache, next is a
     // no-op.
     if (cache.size() == 0 && this.closed) {
       return null;
     }
     if (cache.size() == 0) {
       loadCache();
     }
 
     if (cache.size() > 0) {
       return cache.poll();
     }
     // if we exhausted this scanner before calling close, write out the scan
     // metrics
     writeScanMetrics();
     return null;
   }
 
   @Override
   protected void loadCache() throws IOException {
     Result[] values = null;
     long remainingResultSize = maxScannerResultSize;
     int countdown = this.caching;
     boolean currentRegionDone = false;
     // Values == null means server-side filter has determined we must STOP
     while (remainingResultSize > 0 && countdown > 0
         && nextScanner(countdown, values == null, currentRegionDone)) {
       // Server returns a null values if scanning is to stop. Else,
       // returns an empty array if scanning is to go on and we've just
       // exhausted current region.
       // callWithoutRetries is at this layer. Within the ScannerCallableWithReplicas,
       // we do a callWithRetries
       values = this.caller.callWithoutRetries(smallScanCallable, scannerTimeout);
       this.currentRegion = smallScanCallable.getHRegionInfo();
       long currentTime = System.currentTimeMillis();
       if (this.scanMetrics != null) {
         this.scanMetrics.sumOfMillisSecBetweenNexts.addAndGet(currentTime
             - lastNext);
       }
       lastNext = currentTime;
       if (values != null && values.length > 0) {
         for (int i = 0; i < values.length; i++) {
           Result rs = values[i];
           cache.add(rs);
           // We don't make Iterator here
           for (Cell cell : rs.rawCells()) {
             remainingResultSize -= CellUtil.estimatedHeapSizeOf(cell);
           }
           countdown--;
           this.lastResult = rs;
         }
       }
       if (smallScanCallable.hasMoreResultsContext()) {
         currentRegionDone = !smallScanCallable.getServerHasMoreResults();
       } else {
         currentRegionDone = countdown > 0;
       }
     }
   }
 
   @Override
   protected void initializeScannerInConstruction() throws IOException {
     // No need to initialize the scanner when constructing instance, do it when
     // calling next(). Do nothing here.
   }
 
   @Override
   public void close() {
     if (!scanMetricsPublished) writeScanMetrics();
     closed = true;
   }
 
   @VisibleForTesting
   protected void setScannerCallableFactory(SmallScannerCallableFactory callableFactory) {
     this.callableFactory = callableFactory;
   }
 }