Sub2API v1.0 - AI API 网关（二开初始版本，基于上游 Wei-Shaw/sub2api）

backend/internal/payment/fee.go

@@ -0,0 +1,21 @@
+package payment
+
+import (
+	"github.com/shopspring/decimal"
+)
+
+func CalculatePayAmount(rechargeAmount float64, feeRate float64) string {
+	return CalculatePayAmountForCurrency(rechargeAmount, feeRate, DefaultPaymentCurrency)
+}
+
+// CalculatePayAmountForCurrency 按币种精度计算应付金额，手续费向上取整到该币种最小支付单位。
+func CalculatePayAmountForCurrency(rechargeAmount float64, feeRate float64, currency string) string {
+	fractionDigits := int32(CurrencyMaxFractionDigits(currency))
+	amount := decimal.NewFromFloat(rechargeAmount)
+	if feeRate <= 0 {
+		return amount.StringFixed(fractionDigits)
+	}
+	rate := decimal.NewFromFloat(feeRate)
+	fee := amount.Mul(rate).Div(decimal.NewFromInt(100)).RoundUp(fractionDigits)
+	return amount.Add(fee).StringFixed(fractionDigits)
+}