/**
    *
    * 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.mapred;
  
  import java.io.Closeable;
  import java.io.IOException;
  
  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.hbase.HConstants;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.client.Connection;
  import org.apache.hadoop.hbase.client.HTable;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.client.Table;
  import org.apache.hadoop.hbase.filter.Filter;
  import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
  import org.apache.hadoop.mapred.InputFormat;
  import org.apache.hadoop.mapred.InputSplit;
  import org.apache.hadoop.mapred.JobConf;
  import org.apache.hadoop.mapred.RecordReader;
  import org.apache.hadoop.mapred.Reporter;
  
  /**
   * A Base for {@link TableInputFormat}s. Receives a {@link HTable}, a
   * byte[] of input columns and optionally a {@link Filter}.
   * Subclasses may use other TableRecordReader implementations.
   *
   * Subclasses MUST ensure initializeTable(Connection, TableName) is called for an instance to
   * function properly. Each of the entry points to this class used by the MapReduce framework,
   * {@link #getRecordReader(InputSplit, JobConf, Reporter)} and {@link #getSplits(JobConf, int)},
   * will call {@link #initialize(JobConf)} as a convenient centralized location to handle
   * retrieving the necessary configuration information. If your subclass overrides either of these
   * methods, either call the parent version or call initialize yourself.
   *
   * <p>
   * An example of a subclass:
   * <pre>
   *   class ExampleTIF extends TableInputFormatBase {
   *
   *     {@literal @}Override
   *     protected void initialize(JobConf context) throws IOException {
   *       // We are responsible for the lifecycle of this connection until we hand it over in
   *       // initializeTable.
   *       Connection connection =
   *          ConnectionFactory.createConnection(HBaseConfiguration.create(job));
   *       TableName tableName = TableName.valueOf("exampleTable");
   *       // mandatory. once passed here, TableInputFormatBase will handle closing the connection.
   *       initializeTable(connection, tableName);
   *       byte[][] inputColumns = new byte [][] { Bytes.toBytes("columnA"),
   *         Bytes.toBytes("columnB") };
   *       // mandatory
   *       setInputColumns(inputColumns);
   *       // optional, by default we'll get everything for the given columns.
   *       Filter exampleFilter = new RowFilter(CompareOp.EQUAL, new RegexStringComparator("aa.*"));
   *       setRowFilter(exampleFilter);
   *     }
   *   }
   * </pre>
   */
  
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public abstract class TableInputFormatBase
  implements InputFormat<ImmutableBytesWritable, Result> {
    private static final Log LOG = LogFactory.getLog(TableInputFormatBase.class);
    private byte [][] inputColumns;
    private HTable table;
    private Connection connection;
    private TableRecordReader tableRecordReader;
    private Filter rowFilter;
  
    private static final String NOT_INITIALIZED = "The input format instance has not been properly " +
        "initialized. Ensure you call initializeTable either in your constructor or initialize " +
        "method";
    private static final String INITIALIZATION_ERROR = "Cannot create a record reader because of a" +
              " previous error. Please look at the previous logs lines from" +
              " the task's full log for more details.";
  
    /**
     * Builds a TableRecordReader. If no TableRecordReader was provided, uses
    * the default.
    *
    * @see org.apache.hadoop.mapred.InputFormat#getRecordReader(InputSplit,
    *      JobConf, Reporter)
    */
   @Override
   public RecordReader<ImmutableBytesWritable, Result> getRecordReader(
       InputSplit split, JobConf job, Reporter reporter)
   throws IOException {
     // In case a subclass uses the deprecated approach or calls initializeTable directly
     if (table == null) {
       initialize(job);
     }
     // null check in case our child overrides getTable to not throw.
     try {
       if (getTable() == null) {
         // initialize() must not have been implemented in the subclass.
         throw new IOException(INITIALIZATION_ERROR);
       }
     } catch (IllegalStateException exception) {
       throw new IOException(INITIALIZATION_ERROR, exception);
     }
 
     TableSplit tSplit = (TableSplit) split;
     // if no table record reader was provided use default
     final TableRecordReader trr = this.tableRecordReader == null ? new TableRecordReader() :
         this.tableRecordReader;
     trr.setStartRow(tSplit.getStartRow());
     trr.setEndRow(tSplit.getEndRow());
     trr.setHTable(this.table);
     trr.setInputColumns(this.inputColumns);
     trr.setRowFilter(this.rowFilter);
     trr.init();
     return new RecordReader<ImmutableBytesWritable, Result>() {
 
       @Override
       public void close() throws IOException {
         trr.close();
         closeTable();
       }
 
       @Override
       public ImmutableBytesWritable createKey() {
         return trr.createKey();
       }
 
       @Override
       public Result createValue() {
         return trr.createValue();
       }
 
       @Override
       public long getPos() throws IOException {
         return trr.getPos();
       }
 
       @Override
       public float getProgress() throws IOException {
         return trr.getProgress();
       }
 
       @Override
       public boolean next(ImmutableBytesWritable key, Result value) throws IOException {
         return trr.next(key, value);
       }
     };
   }
 
   /**
    * Calculates the splits that will serve as input for the map tasks.
    *
    * Splits are created in number equal to the smallest between numSplits and
    * the number of {@link org.apache.hadoop.hbase.regionserver.HRegion}s 
    * in the table. If the number of splits is smaller than the number of 
    * {@link org.apache.hadoop.hbase.regionserver.HRegion}s then splits are 
    * spanned across multiple {@link org.apache.hadoop.hbase.regionserver.HRegion}s 
    * and are grouped the most evenly possible. In the case splits are uneven the 
    * bigger splits are placed first in the {@link InputSplit} array.
    *
    * @param job the map task {@link JobConf}
    * @param numSplits a hint to calculate the number of splits (mapred.map.tasks).
    *
    * @return the input splits
    *
    * @see org.apache.hadoop.mapred.InputFormat#getSplits(org.apache.hadoop.mapred.JobConf, int)
    */
   @Override
   public InputSplit[] getSplits(JobConf job, int numSplits) throws IOException {
     if (this.table == null) {
       initialize(job);
     }
     // null check in case our child overrides getTable to not throw.
     try {
       if (getTable() == null) {
         // initialize() must not have been implemented in the subclass.
         throw new IOException(INITIALIZATION_ERROR);
       }
     } catch (IllegalStateException exception) {
       throw new IOException(INITIALIZATION_ERROR, exception);
     }
 
     byte [][] startKeys = this.table.getStartKeys();
     if (startKeys == null || startKeys.length == 0) {
       throw new IOException("Expecting at least one region");
     }
     if (this.inputColumns == null || this.inputColumns.length == 0) {
       throw new IOException("Expecting at least one column");
     }
     int realNumSplits = numSplits > startKeys.length? startKeys.length:
       numSplits;
     InputSplit[] splits = new InputSplit[realNumSplits];
     int middle = startKeys.length / realNumSplits;
     int startPos = 0;
     for (int i = 0; i < realNumSplits; i++) {
       int lastPos = startPos + middle;
       lastPos = startKeys.length % realNumSplits > i ? lastPos + 1 : lastPos;
       String regionLocation = table.getRegionLocation(startKeys[startPos]).
         getHostname();
       splits[i] = new TableSplit(this.table.getName(),
         startKeys[startPos], ((i + 1) < realNumSplits) ? startKeys[lastPos]:
           HConstants.EMPTY_START_ROW, regionLocation);
       LOG.info("split: " + i + "->" + splits[i]);
       startPos = lastPos;
     }
     return splits;
   }
 
   /**
    * Allows subclasses to initialize the table information.
    *
    * @param connection  The Connection to the HBase cluster. MUST be unmanaged. We will close.
    * @param tableName  The {@link TableName} of the table to process.
    * @throws IOException
    */
   protected void initializeTable(Connection connection, TableName tableName) throws IOException {
     if (this.table != null || this.connection != null) {
       LOG.warn("initializeTable called multiple times. Overwriting connection and table " +
           "reference; TableInputFormatBase will not close these old references when done.");
     }
     this.table = (HTable) connection.getTable(tableName);
     this.connection = connection;
   }
 
   /**
    * @param inputColumns to be passed in {@link Result} to the map task.
    */
   protected void setInputColumns(byte [][] inputColumns) {
     this.inputColumns = inputColumns;
   }
 
   /**
    * Allows subclasses to get the {@link HTable}.
    * @deprecated use {@link #getTable()}
    */
   @Deprecated
   protected HTable getHTable() {
     return (HTable) getTable();
   }
 
   /**
    * Allows subclasses to get the {@link Table}.
    */
   protected Table getTable() {
     if (table == null) {
       throw new IllegalStateException(NOT_INITIALIZED);
     }
     return this.table;
   }
 
   /**
    * Allows subclasses to set the {@link HTable}.
    *
    * @param table to get the data from
    * @deprecated use {@link #initializeTable(Connection,TableName)}
    */
   @Deprecated
   protected void setHTable(HTable table) {
     this.table = table;
   }
 
   /**
    * Allows subclasses to set the {@link TableRecordReader}.
    *
    * @param tableRecordReader
    *                to provide other {@link TableRecordReader} implementations.
    */
   protected void setTableRecordReader(TableRecordReader tableRecordReader) {
     this.tableRecordReader = tableRecordReader;
   }
 
   /**
    * Allows subclasses to set the {@link Filter} to be used.
    *
    * @param rowFilter
    */
   protected void setRowFilter(Filter rowFilter) {
     this.rowFilter = rowFilter;
   }
 
   /**
    * Handle subclass specific set up.
    * Each of the entry points used by the MapReduce framework,
    * {@link #getRecordReader(InputSplit, JobConf, Reporter)} and {@link #getSplits(JobConf, int)},
    * will call {@link #initialize(JobConf)} as a convenient centralized location to handle
    * retrieving the necessary configuration information and calling
    * {@link #initializeTable(Connection, TableName)}.
    *
    * Subclasses should implement their initialize call such that it is safe to call multiple times.
    * The current TableInputFormatBase implementation relies on a non-null table reference to decide
    * if an initialize call is needed, but this behavior may change in the future. In particular,
    * it is critical that initializeTable not be called multiple times since this will leak
    * Connection instances.
    *
    */
   protected void initialize(JobConf job) throws IOException {
   }
 
   /**
    * Close the Table and related objects that were initialized via
    * {@link #initializeTable(Connection, TableName)}.
    *
    * @throws IOException
    */
   protected void closeTable() throws IOException {
     close(table, connection);
     table = null;
     connection = null;
   }
 
   private void close(Closeable... closables) throws IOException {
     for (Closeable c : closables) {
       if(c != null) { c.close(); }
     }
   }
 }