/**
 *
 * 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.RegionLocator;
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 Table}, 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 Table table;
  private RegionLocator regionLocator;
  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)
   */
  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)
   */
  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.regionLocator.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 = regionLocator.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 = connection.getTable(tableName);
    this.regionLocator = connection.getRegionLocator(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 Table}.
   */
  protected Table getTable() {
    if (table == null) {
      throw new IllegalStateException(NOT_INITIALIZED);
    }
    return this.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(); }
    }
  }
}