/*
    * 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.shardingsphere.sharding.merge.dql.groupby.aggregation;
  
  import lombok.RequiredArgsConstructor;
  
  import java.math.BigDecimal;
  import java.math.RoundingMode;
  import java.util.Collection;
  import java.util.LinkedHashSet;
  import java.util.List;
  
  /**
   * Distinct average aggregation unit.
   */
  @RequiredArgsConstructor
  public final class DistinctAverageAggregationUnit implements AggregationUnit {
      
      private BigDecimal count;
      
      private BigDecimal sum;
      
      private final Collection<Comparable<?>> countValues = new LinkedHashSet<>();
      
      private final Collection<Comparable<?>> sumValues = new LinkedHashSet<>();
      
      @Override
      public void merge(final List<Comparable<?>> values) {
          if (null == values || null == values.get(0) || null == values.get(1)) {
              return;
          }
          if (countValues.add(values.get(0)) && sumValues.add(values.get(0))) {
              if (null == count) {
                  count = BigDecimal.ZERO;
              }
              if (null == sum) {
                  sum = BigDecimal.ZERO;
              }
              count = count.add(new BigDecimal(values.get(0).toString()));
              sum = sum.add(new BigDecimal(values.get(1).toString()));
          }
      }
      
      @Override
      public Comparable<?> getResult() {
          if (null == count || BigDecimal.ZERO.equals(count)) {
              return count;
          }
          // TODO use metadata to fetch float number precise for database field
          return sum.divide(count, 4, RoundingMode.HALF_UP);
      }
  }