content: /*
   * Copyright 2022 The FeatHub Authors
   *
   * Licensed 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
   *
   *     https://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 com.alibaba.feathub.flink.udf.aggregation;
  
  import org.apache.flink.api.common.typeinfo.TypeInformation;
  import org.apache.flink.api.common.typeinfo.Types;
  import org.apache.flink.table.api.DataTypes;
  import org.apache.flink.table.runtime.typeutils.ExternalTypeInfo;
  import org.apache.flink.table.types.DataType;
  
  import java.util.HashMap;
  import java.util.Map;
  
  /** Aggregate function that counts the number of occurrences of input values. */
  public class ValueCountsAggFunc implements AggFunc<Object, Map<Object, Long>, Map<Object, Long>> {
      private final DataType inDataType;
  
      public ValueCountsAggFunc(DataType inDataType) {
          this.inDataType = inDataType;
      }
  
      @Override
      public void add(Map<Object, Long> accumulator, Object value, long timestamp) {
          accumulator.put(value, accumulator.getOrDefault(value, 0L) + 1);
      }
  
      @Override
      public void merge(Map<Object, Long> target, Map<Object, Long> source) {
          for (Map.Entry<Object, Long> entry : source.entrySet()) {
              final Object key = entry.getKey();
              target.put(key, target.getOrDefault(key, 0L) + entry.getValue());
          }
      }
  
      @Override
      public void retract(Map<Object, Long> accumulator, Object value) {
          long newCnt = accumulator.get(value) - 1;
          if (newCnt == 0) {
              accumulator.remove(value);
          } else {
              accumulator.put(value, newCnt);
          }
      }
  
      @Override
      public void retractAccumulator(Map<Object, Long> target, Map<Object, Long> source) {
          for (Map.Entry<Object, Long> entry : source.entrySet()) {
              final Object key = entry.getKey();
              long newCnt = target.get(key) - entry.getValue();
              if (newCnt == 0) {
                  target.remove(key);
              } else {
                  target.put(key, newCnt);
              }
          }
      }
  
      @Override
      public Map<Object, Long> getResult(Map<Object, Long> accumulator) {
          // TODO: change default value for empty window to empty map.
          if (accumulator.isEmpty()) {
              return null;
          }
          return new HashMap<>(accumulator);
      }
  
      @Override
      public DataType getResultDatatype() {
          return DataTypes.MAP(inDataType, DataTypes.BIGINT());
      }
  
      @Override
      public Map<Object, Long> createAccumulator() {
          return new HashMap<>();
      }
  
      @Override
      public TypeInformation<Map<Object, Long>> getAccumulatorTypeInformation() {
          return Types.MAP(ExternalTypeInfo.of(inDataType), Types.LONG);
      }
  }
  