package money

import (
	"errors"
	"fmt"
	"strconv"
	"strings"
)

// CentsPerYuan 是人民币元与分的固定换算比例。
const CentsPerYuan int64 = 100

var ErrInvalidYuan = errors.New("金额格式不正确")

// ParseYuan 将用户输入的元字符串精确解析为分，不经过 float64。
// 支持 "12"、"12.3"、"12.34"、"-1.20"；超过两位小数直接拒绝。
func ParseYuan(value string) (int64, error) {
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return 0, ErrInvalidYuan
	}
	sign := int64(1)
	if strings.HasPrefix(trimmed, "-") {
		sign = -1
		trimmed = strings.TrimPrefix(trimmed, "-")
	} else if strings.HasPrefix(trimmed, "+") {
		trimmed = strings.TrimPrefix(trimmed, "+")
	}
	if trimmed == "" {
		return 0, ErrInvalidYuan
	}
	parts := strings.Split(trimmed, ".")
	if len(parts) > 2 {
		return 0, ErrInvalidYuan
	}
	wholeText := parts[0]
	if wholeText == "" {
		wholeText = "0"
	}
	whole, err := strconv.ParseInt(wholeText, 10, 64)
	if err != nil || whole < 0 {
		return 0, ErrInvalidYuan
	}
	fraction := int64(0)
	if len(parts) == 2 {
		fracText := parts[1]
		if len(fracText) > 2 {
			return 0, ErrInvalidYuan
		}
		fracText = fracText + strings.Repeat("0", 2-len(fracText))
		if fracText == "" {
			fracText = "00"
		}
		fraction, err = strconv.ParseInt(fracText, 10, 64)
		if err != nil || fraction < 0 || fraction >= CentsPerYuan {
			return 0, ErrInvalidYuan
		}
	}
	if whole > (1<<62)/CentsPerYuan {
		return 0, ErrInvalidYuan
	}
	return sign * (whole*CentsPerYuan + fraction), nil
}

// Format 将分精确格式化为两位小数，例如 1234 -> "12.34"。
// 全程使用整数运算，不经过 float64，也不做四舍五入。
func Format(cent int64) string {
	sign := ""
	value := cent
	if value < 0 {
		sign = "-"
		value = -value
	}
	return fmt.Sprintf("%s%d.%02d", sign, value/CentsPerYuan, value%CentsPerYuan)
}

func FormatWithSymbol(cent int64) string {
	return "¥" + Format(cent)
}

func MinCent(a, b int64) int64 {
	if a < b {
		return a
	}
	return b
}

func MaxCent(a, b int64) int64 {
	if a > b {
		return a
	}
	return b
}