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.table.types.DataType;
  
  import org.apache.flink.shaded.guava30.com.google.common.collect.Iterables;
  
  /**
   * Aggregate function that get the min or max.
   *
   * <p>Implementation is optimized based on the assumption that no retraction is required.
   */
  public class MinMaxAggFuncWithoutRetract<T extends Comparable<T>> extends MinMaxAggFunc<T> {
      public MinMaxAggFuncWithoutRetract(DataType inDataType, boolean isMin) {
          super(inDataType, isMin);
      }
  
      @Override
      public void add(MinMaxAccumulator<T> accumulator, T value, long timestamp) {
          if (accumulator.values.isEmpty()) {
              accumulator.values.put(value, 1L);
              return;
          }
  
          T currentValue = Iterables.getOnlyElement(accumulator.values.keySet());
  
          if ((isMin && currentValue.compareTo(value) > 0)
                  || (!isMin && currentValue.compareTo(value) < 0)) {
              accumulator.values.clear();
              accumulator.values.put(value, 1L);
          }
      }
  
      @Override
      public void merge(MinMaxAccumulator<T> target, MinMaxAccumulator<T> source) {
          add(target, Iterables.getOnlyElement(source.values.keySet()), -1L);
      }
  
      @Override
      public void retract(MinMaxAccumulator<T> accumulator, T value) {
          throw new UnsupportedOperationException();
      }
  
      @Override
      public void retractAccumulator(MinMaxAccumulator<T> target, MinMaxAccumulator<T> source) {
          throw new UnsupportedOperationException();
      }
  
      @Override
      public T getResult(MinMaxAccumulator<T> accumulator) {
          if (accumulator.values.isEmpty()) {
              return null;
          }
          return Iterables.getOnlyElement(accumulator.values.keySet());
      }
  }
  