/**
    *
    * 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.IOException;
  import java.util.ArrayList;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.client.Result;
  import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.mapred.JobConf;
  import org.apache.hadoop.mapred.MapReduceBase;
  import org.apache.hadoop.mapred.OutputCollector;
  import org.apache.hadoop.mapred.Reporter;
  
  
  /**
   * Extract grouping columns from input record
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class GroupingTableMap
  extends MapReduceBase
  implements TableMap<ImmutableBytesWritable,Result> {
  
    /**
     * JobConf parameter to specify the columns used to produce the key passed to
     * collect from the map phase
     */
    public static final String GROUP_COLUMNS =
      "hbase.mapred.groupingtablemap.columns";
  
    protected byte [][] columns;
  
    /**
     * Use this before submitting a TableMap job. It will appropriately set up the
     * JobConf.
     *
     * @param table table to be processed
     * @param columns space separated list of columns to fetch
     * @param groupColumns space separated list of columns used to form the key
     * used in collect
     * @param mapper map class
     * @param job job configuration object
     */
    @SuppressWarnings("unchecked")
    public static void initJob(String table, String columns, String groupColumns,
      Class<? extends TableMap> mapper, JobConf job) {
  
      TableMapReduceUtil.initTableMapJob(table, columns, mapper,
          ImmutableBytesWritable.class, Result.class, job);
      job.set(GROUP_COLUMNS, groupColumns);
    }
  
    @Override
    public void configure(JobConf job) {
      super.configure(job);
      String[] cols = job.get(GROUP_COLUMNS, "").split(" ");
      columns = new byte[cols.length][];
      for(int i = 0; i < cols.length; i++) {
        columns[i] = Bytes.toBytes(cols[i]);
      }
    }
  
    /**
     * Extract the grouping columns from value to construct a new key.
     *
     * Pass the new key and value to reduce.
     * If any of the grouping columns are not found in the value, the record is skipped.
     * @param key
     * @param value
     * @param output
     * @param reporter
     * @throws IOException
     */
    @Override
    public void map(ImmutableBytesWritable key, Result value,
        OutputCollector<ImmutableBytesWritable,Result> output,
       Reporter reporter) throws IOException {
 
     byte[][] keyVals = extractKeyValues(value);
     if(keyVals != null) {
       ImmutableBytesWritable tKey = createGroupKey(keyVals);
       output.collect(tKey, value);
     }
   }
 
   /**
    * Extract columns values from the current record. This method returns
    * null if any of the columns are not found.
    *
    * Override this method if you want to deal with nulls differently.
    *
    * @param r
    * @return array of byte values
    */
   protected byte[][] extractKeyValues(Result r) {
     byte[][] keyVals = null;
     ArrayList<byte[]> foundList = new ArrayList<byte[]>();
     int numCols = columns.length;
     if (numCols > 0) {
       for (Cell value: r.listCells()) {
         byte [] column = KeyValue.makeColumn(CellUtil.cloneFamily(value),
             CellUtil.cloneQualifier(value));
         for (int i = 0; i < numCols; i++) {
           if (Bytes.equals(column, columns[i])) {
             foundList.add(CellUtil.cloneValue(value));
             break;
           }
         }
       }
       if(foundList.size() == numCols) {
         keyVals = foundList.toArray(new byte[numCols][]);
       }
     }
     return keyVals;
   }
 
   /**
    * Create a key by concatenating multiple column values.
    * Override this function in order to produce different types of keys.
    *
    * @param vals
    * @return key generated by concatenating multiple column values
    */
   protected ImmutableBytesWritable createGroupKey(byte[][] vals) {
     if(vals == null) {
       return null;
     }
     StringBuilder sb =  new StringBuilder();
     for(int i = 0; i < vals.length; i++) {
       if(i > 0) {
         sb.append(" ");
       }
       sb.append(Bytes.toString(vals[i]));
     }
     return new ImmutableBytesWritable(Bytes.toBytesBinary(sb.toString()));
   }
 }