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

backend/internal/service/payment_amounts.go

@@ -0,0 +1,48 @@
+package service
+
+import (
+	"math"
+
+	"github.com/Wei-Shaw/sub2api/internal/payment"
+	"github.com/shopspring/decimal"
+)
+
+const defaultBalanceRechargeMultiplier = 1.0
+
+func normalizeBalanceRechargeMultiplier(multiplier float64) float64 {
+	if math.IsNaN(multiplier) || math.IsInf(multiplier, 0) || multiplier <= 0 {
+		return defaultBalanceRechargeMultiplier
+	}
+	return multiplier
+}
+
+// normalizeSubscriptionUSDToCNYRate 将非法值归一为 0（换算关闭）。
+// 与余额倍率不同，0 是合法状态：表示订阅保持 price 直付的存量行为。
+func normalizeSubscriptionUSDToCNYRate(rate float64) float64 {
+	if math.IsNaN(rate) || math.IsInf(rate, 0) || rate < 0 {
+		return 0
+	}
+	return rate
+}
+
+func calculateCreditedBalance(paymentAmount, multiplier float64) float64 {
+	return decimal.NewFromFloat(paymentAmount).
+		Mul(decimal.NewFromFloat(normalizeBalanceRechargeMultiplier(multiplier))).
+		Round(2).
+		InexactFloat64()
+}
+
+func calculateGatewayRefundAmount(orderAmount, payAmount, refundAmount float64, currency string) float64 {
+	if orderAmount <= 0 || payAmount <= 0 || refundAmount <= 0 {
+		return 0
+	}
+	fractionDigits := int32(payment.CurrencyMaxFractionDigits(currency))
+	if math.Abs(refundAmount-orderAmount) <= paymentAmountToleranceForCurrency(currency) {
+		return decimal.NewFromFloat(payAmount).Round(fractionDigits).InexactFloat64()
+	}
+	return decimal.NewFromFloat(payAmount).
+		Mul(decimal.NewFromFloat(refundAmount)).
+		Div(decimal.NewFromFloat(orderAmount)).
+		Round(fractionDigits).
+		InexactFloat64()
+}