content: /**
   * 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.apex.malhar.stream.sample.complete;
  
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.apex.malhar.lib.window.Accumulation;
  
  /**
   * Specialized TopNByKey accumulation for AutoComplete Example.
   *
   * @since 3.5.0
   */
  public class TopNByKey implements
      Accumulation<CompletionCandidate, Map<String, Long>, List<CompletionCandidate>>
  {
    int n = 10;
  
    Comparator comparator;
  
    public void setN(int n)
    {
      this.n = n;
    }
  
    public void setComparator(Comparator comparator)
    {
      this.comparator = comparator;
    }
  
    @Override
    public Map<String, Long> defaultAccumulatedValue()
    {
      return new HashMap<>();
    }
  
    /**
     * Accumulate the input. Update the entry in the Accumulation Map if the key of the input is existed, create a
     * new entry otherwise.
     * @param accumulatedValue
     * @param input
     * @return
     */
    @Override
    public Map<String, Long> accumulate(Map<String, Long> accumulatedValue, CompletionCandidate input)
    {
      accumulatedValue.put(input.getValue(), input.getCount());
      return accumulatedValue;
    }
  
    /**
     * Merge two Maps together. For every key, keep the larger value in the resulted Map.
     * @param accumulatedValue1
     * @param accumulatedValue2
     * @return
     */
    @Override
    public Map<String, Long> merge(Map<String, Long> accumulatedValue1, Map<String, Long> accumulatedValue2)
    {
      for (Map.Entry<String, Long> entry : accumulatedValue2.entrySet()) {
        if (accumulatedValue1.containsKey(entry.getKey()) && accumulatedValue1.get(entry.getKey()) > entry.getValue()) {
          continue;
        }
        accumulatedValue1.put(entry.getKey(), entry.getValue());
      }
      return accumulatedValue1;
    }
  
    /**
     * Loop through the Accumulation Map to get the top n entries based on their values, return a list containing
     * those entries.
     * @param accumulatedValue
     * @return
     */
    @Override
    public List<CompletionCandidate> getOutput(Map<String, Long> accumulatedValue)
    {
      LinkedList<CompletionCandidate> result = new LinkedList<>();
      for (Map.Entry<String, Long> entry : accumulatedValue.entrySet()) {
        int k = 0;
        for (CompletionCandidate inMemory : result) {
          if (entry.getValue() > inMemory.getCount()) {
            break;
          }
          k++;
        }
        result.add(k, new CompletionCandidate(entry.getKey(), entry.getValue()));
        if (result.size() > n) {
          result.remove(result.get(result.size() - 1));
        }
      }
      return result;
    }
  
    @Override
    public List<CompletionCandidate> getRetraction(List<CompletionCandidate> value)
    {
      return new LinkedList<>();
    }
  }
  