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.table.types.DataType;
  
  import java.io.Serializable;
  
  /**
   * Interface of aggregation function. The aggregation function can aggregate any number of records
   * with its timestamp and get the aggregation result.
   */
  public interface AggFunc<IN_T, OUT_T, ACC_T> extends Serializable {
      /**
       * Adds the given input value to the given accumulator.
       *
       * @param value The value.
       * @param timestamp The timestamp of the value.
       */
      void add(ACC_T accumulator, IN_T value, long timestamp);
  
      /** Merges the contents of the source accumulator into the target accumulator. */
      void merge(ACC_T target, ACC_T source);
  
      /**
       * Retracts the given input value from the given accumulator.
       *
       * @param accumulator The accumulator to retract the value from.
       * @param value The value to be retracted.
       */
      void retract(ACC_T accumulator, IN_T value);
  
      /** Retracts the contents of the source accumulator from the target accumulator. */
      void retractAccumulator(ACC_T target, ACC_T source);
  
      /** @return The aggregation result. */
      OUT_T getResult(ACC_T accumulator);
  
      /** @return The DataType of the aggregation result. */
      DataType getResultDatatype();
  
      /** @return The new accumulator of the aggregation function. */
      ACC_T createAccumulator();
  
      /** @return The type info of the accumulator. */
      TypeInformation<ACC_T> getAccumulatorTypeInformation();
  }
  