/*
 * 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.List;

/**
 * Average aggregation unit.
 */
@RequiredArgsConstructor
public final class AverageAggregationUnit implements AggregationUnit {
    
    private BigDecimal count;
    
    private BigDecimal sum;
    
    @Override
    public void merge(final List<Comparable<?>> values) {
        if (null == values || null == values.get(0) || null == values.get(1)) {
            return;
        }
        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.compareTo(count) == 0) {
            return count;
        }
        // TODO use metadata to fetch float number precise for database field
        return sum.divide(count, 4, RoundingMode.HALF_UP);
    }
}
