feat: add Airwallex payments and multi-currency support

backend/internal/service/payment_currency.go

@@ -0,0 +1,28 @@
+package service
+
+import (
+	"strings"
+
+	dbent "github.com/Wei-Shaw/sub2api/ent"
+	"github.com/Wei-Shaw/sub2api/internal/payment"
+)
+
+func paymentProviderConfigCurrency(providerKey string, cfg map[string]string) string {
+	switch strings.TrimSpace(providerKey) {
+	case payment.TypeStripe, payment.TypeAirwallex:
+		currency, err := payment.NormalizePaymentCurrency(cfg["currency"])
+		if err == nil {
+			return currency
+		}
+	}
+	return payment.DefaultPaymentCurrency
+}
+
+func PaymentOrderCurrency(order *dbent.PaymentOrder) string {
+	if snapshot := psOrderProviderSnapshot(order); snapshot != nil {
+		if currency, err := payment.NormalizePaymentCurrency(snapshot.Currency); err == nil {
+			return currency
+		}
+	}
+	return payment.DefaultPaymentCurrency
+}