/**
    * 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.mapreduce;
  
  import java.io.IOException;
  import java.lang.reflect.Method;
  import java.util.Map;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.client.ResultScanner;
  import org.apache.hadoop.hbase.client.Scan;
  import org.apache.hadoop.hbase.client.ScannerCallable;
  import org.apache.hadoop.hbase.client.Table;
  import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
  import org.apache.hadoop.hbase.DoNotRetryIOException;
  import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.mapreduce.Counter;
  import org.apache.hadoop.mapreduce.InputSplit;
  import org.apache.hadoop.mapreduce.TaskAttemptContext;
  import org.apache.hadoop.util.StringUtils;
  
  import com.google.common.annotations.VisibleForTesting;
  
  /**
   * Iterate over an HBase table data, return (ImmutableBytesWritable, Result)
   * pairs.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class TableRecordReaderImpl {
    public static final String LOG_PER_ROW_COUNT
      = "hbase.mapreduce.log.scanner.rowcount";
  
    static final Log LOG = LogFactory.getLog(TableRecordReaderImpl.class);
  
    // HBASE_COUNTER_GROUP_NAME is the name of mapreduce counter group for HBase
    @VisibleForTesting
    static final String HBASE_COUNTER_GROUP_NAME = "HBase Counters";
    private ResultScanner scanner = null;
    private Scan scan = null;
    private Scan currentScan = null;
    private Table htable = null;
    private byte[] lastSuccessfulRow = null;
    private ImmutableBytesWritable key = null;
    private Result value = null;
    private TaskAttemptContext context = null;
    private Method getCounter = null;
    private long numRestarts = 0;
    private long numStale = 0;
    private long timestamp;
    private int rowcount;
    private boolean logScannerActivity = false;
    private int logPerRowCount = 100;
  
    /**
     * Restart from survivable exceptions by creating a new scanner.
     *
     * @param firstRow  The first row to start at.
     * @throws IOException When restarting fails.
     */
    public void restart(byte[] firstRow) throws IOException {
      currentScan = new Scan(scan);
      currentScan.setStartRow(firstRow);
      currentScan.setScanMetricsEnabled(true);
      if (this.scanner != null) {
        if (logScannerActivity) {
          LOG.info("Closing the previously opened scanner object.");
        }
        this.scanner.close();
      }
      this.scanner = this.htable.getScanner(currentScan);
      if (logScannerActivity) {
        LOG.info("Current scan=" + currentScan.toString());
        timestamp = System.currentTimeMillis();
        rowcount = 0;
      }
    }
  
   /**
    * In new mapreduce APIs, TaskAttemptContext has two getCounter methods
    * Check if getCounter(String, String) method is available.
    * @return The getCounter method or null if not available.
    * @throws IOException
    */
   protected static Method retrieveGetCounterWithStringsParams(TaskAttemptContext context)
   throws IOException {
     Method m = null;
     try {
       m = context.getClass().getMethod("getCounter",
         new Class [] {String.class, String.class});
     } catch (SecurityException e) {
       throw new IOException("Failed test for getCounter", e);
     } catch (NoSuchMethodException e) {
       // Ignore
     }
     return m;
   }
 
   /**
    * Sets the HBase table.
    *
    * @param htable  The {@link org.apache.hadoop.hbase.HTableDescriptor} to scan.
    */
   public void setHTable(Table htable) {
     Configuration conf = htable.getConfiguration();
     logScannerActivity = conf.getBoolean(
       ScannerCallable.LOG_SCANNER_ACTIVITY, false);
     logPerRowCount = conf.getInt(LOG_PER_ROW_COUNT, 100);
     this.htable = htable;
   }
 
   /**
    * Sets the scan defining the actual details like columns etc.
    *
    * @param scan  The scan to set.
    */
   public void setScan(Scan scan) {
     this.scan = scan;
   }
 
   /**
    * Build the scanner. Not done in constructor to allow for extension.
    *
    * @throws IOException, InterruptedException
    */
   public void initialize(InputSplit inputsplit,
       TaskAttemptContext context) throws IOException,
       InterruptedException {
     if (context != null) {
       this.context = context;
       getCounter = retrieveGetCounterWithStringsParams(context);
     }
     restart(scan.getStartRow());
   }
 
   /**
    * Closes the split.
    *
    *
    */
   public void close() {
     this.scanner.close();
     try {
       this.htable.close();
     } catch (IOException ioe) {
       LOG.warn("Error closing table", ioe);
     }
   }
 
   /**
    * Returns the current key.
    *
    * @return The current key.
    * @throws IOException
    * @throws InterruptedException When the job is aborted.
    */
   public ImmutableBytesWritable getCurrentKey() throws IOException,
       InterruptedException {
     return key;
   }
 
   /**
    * Returns the current value.
    *
    * @return The current value.
    * @throws IOException When the value is faulty.
    * @throws InterruptedException When the job is aborted.
    */
   public Result getCurrentValue() throws IOException, InterruptedException {
     return value;
   }
 
 
   /**
    * Positions the record reader to the next record.
    *
    * @return <code>true</code> if there was another record.
    * @throws IOException When reading the record failed.
    * @throws InterruptedException When the job was aborted.
    */
   public boolean nextKeyValue() throws IOException, InterruptedException {
     if (key == null) key = new ImmutableBytesWritable();
     if (value == null) value = new Result();
     try {
       try {
         value = this.scanner.next();
         if (value != null && value.isStale()) numStale++;
         if (logScannerActivity) {
           rowcount ++;
           if (rowcount >= logPerRowCount) {
             long now = System.currentTimeMillis();
             LOG.info("Mapper took " + (now-timestamp)
               + "ms to process " + rowcount + " rows");
             timestamp = now;
             rowcount = 0;
           }
         }
       } catch (IOException e) {
         // do not retry if the exception tells us not to do so
         if (e instanceof DoNotRetryIOException) {
           throw e;
         }
         // try to handle all other IOExceptions by restarting
         // the scanner, if the second call fails, it will be rethrown
         LOG.info("recovered from " + StringUtils.stringifyException(e));
         if (lastSuccessfulRow == null) {
           LOG.warn("We are restarting the first next() invocation," +
               " if your mapper has restarted a few other times like this" +
               " then you should consider killing this job and investigate" +
               " why it's taking so long.");
         }
         if (lastSuccessfulRow == null) {
           restart(scan.getStartRow());
         } else {
           restart(lastSuccessfulRow);
           scanner.next();    // skip presumed already mapped row
         }
         value = scanner.next();
         if (value != null && value.isStale()) numStale++;
         numRestarts++;
       }
       if (value != null && value.size() > 0) {
         key.set(value.getRow());
         lastSuccessfulRow = key.get();
         return true;
       }
 
       updateCounters();
       return false;
     } catch (IOException ioe) {
       if (logScannerActivity) {
         long now = System.currentTimeMillis();
         LOG.info("Mapper took " + (now-timestamp)
           + "ms to process " + rowcount + " rows");
         LOG.info(ioe);
         String lastRow = lastSuccessfulRow == null ?
           "null" : Bytes.toStringBinary(lastSuccessfulRow);
         LOG.info("lastSuccessfulRow=" + lastRow);
       }
       throw ioe;
     }
   }
 
   /**
    * If hbase runs on new version of mapreduce, RecordReader has access to
    * counters thus can update counters based on scanMetrics.
    * If hbase runs on old version of mapreduce, it won't be able to get
    * access to counters and TableRecorderReader can't update counter values.
    * @throws IOException
    */
   private void updateCounters() throws IOException {
     ScanMetrics scanMetrics = currentScan.getScanMetrics();
     if (scanMetrics == null) {
       return;
     }
 
     updateCounters(scanMetrics, numRestarts, getCounter, context, numStale);
   }
 
   protected static void updateCounters(ScanMetrics scanMetrics, long numScannerRestarts,
       Method getCounter, TaskAttemptContext context, long numStale) {
     // we can get access to counters only if hbase uses new mapreduce APIs
     if (getCounter == null) {
       return;
     }
 
     try {
       for (Map.Entry<String, Long> entry:scanMetrics.getMetricsMap().entrySet()) {
         Counter ct = (Counter)getCounter.invoke(context,
             HBASE_COUNTER_GROUP_NAME, entry.getKey());
 
         ct.increment(entry.getValue());
       }
       ((Counter) getCounter.invoke(context, HBASE_COUNTER_GROUP_NAME,
           "NUM_SCANNER_RESTARTS")).increment(numScannerRestarts);
       ((Counter) getCounter.invoke(context, HBASE_COUNTER_GROUP_NAME,
           "NUM_SCAN_RESULTS_STALE")).increment(numStale);
     } catch (Exception e) {
       LOG.debug("can't update counter." + StringUtils.stringifyException(e));
     }
   }
 
   /**
    * The current progress of the record reader through its data.
    *
    * @return A number between 0.0 and 1.0, the fraction of the data read.
    */
   public float getProgress() {
     // Depends on the total number of tuples
     return 0;
   }
 
 }