/**
 * 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.mapreduce.lib.aggregate;

import java.util.ArrayList;
import java.util.Map.Entry;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.MRJobConfig;

/** 
 * This class implements the common functionalities of 
 * the subclasses of ValueAggregatorDescriptor class.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class ValueAggregatorBaseDescriptor 
    implements ValueAggregatorDescriptor {

  static public final String UNIQ_VALUE_COUNT = "UniqValueCount";

  static public final String LONG_VALUE_SUM = "LongValueSum";

  static public final String DOUBLE_VALUE_SUM = "DoubleValueSum";

  static public final String VALUE_HISTOGRAM = "ValueHistogram";
  
  static public final String LONG_VALUE_MAX = "LongValueMax";
  
  static public final String LONG_VALUE_MIN = "LongValueMin";
  
  static public final String STRING_VALUE_MAX = "StringValueMax";
  
  static public final String STRING_VALUE_MIN = "StringValueMin";
  
  public String inputFile = null;

  private static class MyEntry implements Entry<Text, Text> {
    Text key;

    Text val;

    public Text getKey() {
      return key;
    }

    public Text getValue() {
      return val;
    }

    public Text setValue(Text val) {
      this.val = val;
      return val;
    }

    public MyEntry(Text key, Text val) {
      this.key = key;
      this.val = val;
    }
  }

  /**
   * 
   * @param type the aggregation type
   * @param id the aggregation id
   * @param val the val associated with the id to be aggregated
   * @return an Entry whose key is the aggregation id prefixed with 
   * the aggregation type.
   */
  public static Entry<Text, Text> generateEntry(String type, 
      String id, Text val) {
    Text key = new Text(type + TYPE_SEPARATOR + id);
    return new MyEntry(key, val);
  }

  /**
   * 
   * @param type the aggregation type
   * @param uniqCount the limit in the number of unique values to keep, 
   *                  if type is UNIQ_VALUE_COUNT 
   * @return a value aggregator of the given type.
   */
  static public ValueAggregator generateValueAggregator(String type, long uniqCount) {
    if (type.compareToIgnoreCase(LONG_VALUE_SUM) == 0) {
      return new LongValueSum();
    } if (type.compareToIgnoreCase(LONG_VALUE_MAX) == 0) {
      return new LongValueMax();
    } else if (type.compareToIgnoreCase(LONG_VALUE_MIN) == 0) {
      return new LongValueMin();
    } else if (type.compareToIgnoreCase(STRING_VALUE_MAX) == 0) {
      return new StringValueMax();
    } else if (type.compareToIgnoreCase(STRING_VALUE_MIN) == 0) {
      return new StringValueMin();
    } else if (type.compareToIgnoreCase(DOUBLE_VALUE_SUM) == 0) {
      return new DoubleValueSum();
    } else if (type.compareToIgnoreCase(UNIQ_VALUE_COUNT) == 0) {
      return new UniqValueCount(uniqCount);
    } else if (type.compareToIgnoreCase(VALUE_HISTOGRAM) == 0) {
      return new ValueHistogram();
    }
    return null;
  }

  /**
   * Generate 1 or 2 aggregation-id/value pairs for the given key/value pair.
   * The first id will be of type LONG_VALUE_SUM, with "record_count" as
   * its aggregation id. If the input is a file split,
   * the second id of the same type will be generated too, with the file name 
   * as its aggregation id. This achieves the behavior of counting the total 
   * number of records in the input data, and the number of records 
   * in each input file.
   * 
   * @param key
   *          input key
   * @param val
   *          input value
   * @return a list of aggregation id/value pairs. An aggregation id encodes an
   *         aggregation type which is used to guide the way to aggregate the
   *         value in the reduce/combiner phrase of an Aggregate based job.
   */
  public ArrayList<Entry<Text, Text>> generateKeyValPairs(Object key,
                                                          Object val) {
    ArrayList<Entry<Text, Text>> retv = new ArrayList<Entry<Text, Text>>();
    String countType = LONG_VALUE_SUM;
    String id = "record_count";
    Entry<Text, Text> e = generateEntry(countType, id, ONE);
    if (e != null) {
      retv.add(e);
    }
    if (this.inputFile != null) {
      e = generateEntry(countType, this.inputFile, ONE);
      if (e != null) {
        retv.add(e);
      }
    }
    return retv;
  }

  /**
   * get the input file name.
   * 
   * @param conf a configuration object
   */
  public void configure(Configuration conf) {
    this.inputFile = conf.get(MRJobConfig.MAP_INPUT_FILE);
  }
}