/**
 * 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.mahout.ga.watchmaker.cd.tool;

import java.io.IOException;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

import com.google.common.base.Preconditions;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

/**
 * Combines attribute values into a String.<br>
 * <ul>
 * <li>For Numerical attributes, the string contains the min and max values found.</li>
 * <li>For Categorical attributes, the string contains the distinct values found.</li>
 * </ul>
 * 
 * See Descriptors, for more informations about the job parameter
 */
public class ToolCombiner extends Reducer<LongWritable, Text, LongWritable, Text> {

  private final Collection<String> distinct = new HashSet<String>();

  private Descriptors descriptors;

  @Override
  protected void reduce(LongWritable key,
                        Iterable<Text> values,
                        Context context) throws IOException, InterruptedException {
    context.write(key, new Text(createDescription((int) key.get(), values.iterator())));
  }

  @Override
  protected void setup(Context context) throws IOException, InterruptedException {
    super.setup(context);
    String descriptors = context.getConfiguration().get(ToolMapper.ATTRIBUTES);

    if (descriptors != null) {
      configure(descriptors.toCharArray());
    }
  }

  void configure(char[] descriptors) {
    Preconditions.checkArgument(descriptors != null && descriptors.length > 0, "descriptors null or empty");
    this.descriptors = new Descriptors(descriptors);
  }

  /**
   * Generate a String description for a given attribute from its available values.
   * 
   * @param index
   *          attribute index
   * @param values
   *          available values
   * @throws IllegalArgumentException
   *           if the attribute should be ignored.
   */
  String createDescription(int index, Iterator<Text> values) {
    if (descriptors.isNominal(index)) {
      return nominalDescription(values);
    } else if (descriptors.isNumerical(index)) {
      return numericalDescription(values);
    } else {
      throw new IllegalArgumentException("An ignored attribute should never reach the Combiner");
    }
  }

  String nominalDescription(Iterator<Text> values) {
    // distinct values
    distinct.clear();
    while (values.hasNext()) {
      distinct.add(values.next().toString());
    }

    return DescriptionUtils.createNominalDescription(distinct);
  }

  static String numericalDescription(Iterator<Text> values) {
    double min = Double.POSITIVE_INFINITY;
    double max = Double.NEGATIVE_INFINITY;

    while (values.hasNext()) {
      double value = Double.parseDouble(values.next().toString());
      if (value < min) {
        min = value;
      } else if (value > max) {
        max = value;
      }
    }

    return DescriptionUtils.createNumericalDescription(min, max);
  }
}