package utils

import (
	"github.com/shopspring/decimal"
	"sort"
)

// Average 取平均值
func Average(numbers []decimal.Decimal) decimal.Decimal {
	if len(numbers) == 0 {
		return decimal.Decimal{}
	}
	if len(numbers) == 1 {
		return numbers[0]
	}
	var sum decimal.Decimal
	for _, d := range numbers {
		sum = sum.Add(d)
	}
	return sum.Div(decimal.NewFromInt(int64(len(numbers))))
}

// Deviation 偏差
func Deviation(numbers []decimal.Decimal) decimal.Decimal {
	if len(numbers) == 0 || len(numbers) == 1 {
		return decimal.Decimal{}
	}
	avgNum := Average(numbers)
	var diffSquaredSum decimal.Decimal
	for _, n := range numbers {
		diff := n.Sub(avgNum)
		diffSquaredSum = diffSquaredSum.Add(diff.Mul(diff))
	}
	return diffSquaredSum.Div(decimal.NewFromInt(int64(len(numbers))))
}

// TotalDeviation 总差
func TotalDeviation(numbers []decimal.Decimal, average decimal.Decimal) decimal.Decimal {
	if len(numbers) < 2 {
		return decimal.Zero
	}

	n := len(numbers)
	ratio := decimal.NewFromFloat(0.02)
	length := decimal.NewFromInt(int64(n)).Mul(ratio).Ceil().IntPart()
	if length >= int64(n) {
		return decimal.Zero
	}

	sort.Slice(numbers, func(i, j int) bool {
		return numbers[i].LessThan(numbers[j])
	})

	minPart := numbers[:length-1]
	maxPart := numbers[length:]

	minAverage := Average(minPart)
	maxAverage := Average(maxPart)

	minDiff := minAverage.Sub(average).Abs()
	maxDiff := maxAverage.Sub(average).Abs()

	return decimal.Max(minDiff, maxDiff)
}