import cn.hutool.core.util.NumberUtil;
import com.google.common.collect.Lists;
import lombok.Builder;
import lombok.Getter;
import lombok.Setter;

import java.math.BigDecimal;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;

public class BatchReduceTest {

    @SafeVarargs
    static <T> List<BigDecimal> batchSum(List<T> list, Function<T, Number>... functions) {
        if (functions == null || functions.length == 0) {
            return Collections.emptyList();
        }
        List<BigDecimal> result = Lists.newArrayListWithCapacity(functions.length);
        for (int i = 0; i < functions.length; i++) {
            // 初始化值，可考虑BigDecimal.Zero
            result.add(null);
        }
        for (T t : list) {
            for (int j = 0; j < functions.length; j++) {
                Function<T, Number> function = functions[j];
                Number apply = function.apply(t);
                Number number = result.get(j);
                if (number == null) {
                    result.set(j, new BigDecimal(apply + ""));
                } else {
                    result.set(j, NumberUtil.add(apply, number));
                }
            }
        }
        return result;
    }

    @Setter
    @Getter
    @Builder
    static class Foo {
        private Integer integer;
        private BigDecimal bigDecimal;
    }

    public static void main(String[] args) {
        Foo foo1 = Foo.builder().integer(1).bigDecimal(new BigDecimal("10")).build();
        Foo foo2 = Foo.builder().integer(2).bigDecimal(new BigDecimal("12.3")).build();
        Foo foo3 = Foo.builder().integer(8).bigDecimal(new BigDecimal("2")).build();
        List<Foo> fooList = Lists.newArrayList(foo1, foo2, foo3);
        List<BigDecimal> numbers = batchSum(fooList, Foo::getInteger, Foo::getBigDecimal);
        System.out.println(numbers.get(0).intValue() == 11);
        System.out.println(numbers.get(1).compareTo(new BigDecimal("24.3")) == 0);
        System.out.println(numbers);
    }
}