From 0b26acac0798a43935bd6a71be260cac3b9acfe2 Mon Sep 17 00:00:00 2001
From: wucm667 <stevenwucongmin@gmail.com>
Date: Sun, 2 Aug 2026 20:27:44 +0800
Subject: [PATCH] fix(payment): make Stripe refunds idempotent

---
 backend/internal/payment/provider/stripe.go   |  1 +
 .../internal/payment/provider/stripe_test.go  | 70 +++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 backend/internal/payment/provider/stripe_test.go

diff --git a/backend/internal/payment/provider/stripe.go b/backend/internal/payment/provider/stripe.go
index 59e31f8122..f09cc21b2d 100644
--- a/backend/internal/payment/provider/stripe.go
+++ b/backend/internal/payment/provider/stripe.go
@@ -230,6 +230,7 @@ func (s *Stripe) Refund(ctx context.Context, req payment.RefundRequest) (*paymen
 		Amount:        stripe.Int64(amountInMinorUnit),
 		Reason:        stripe.String(string(stripe.RefundReasonRequestedByCustomer)),
 	}
+	params.SetIdempotencyKey(fmt.Sprintf("re-%s-%d", req.OrderID, amountInMinorUnit))
 	params.Context = ctx
 
 	r, err := s.sc.V1Refunds.Create(ctx, params)
diff --git a/backend/internal/payment/provider/stripe_test.go b/backend/internal/payment/provider/stripe_test.go
new file mode 100644
index 0000000000..9c327898ff
--- /dev/null
+++ b/backend/internal/payment/provider/stripe_test.go
@@ -0,0 +1,70 @@
+//go:build unit
+
+package provider
+
+import (
+	"bytes"
+	"context"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/payment"
+	"github.com/stretchr/testify/require"
+	stripe "github.com/stripe/stripe-go/v85"
+)
+
+type stripeRefundBackend struct {
+	params []*stripe.RefundCreateParams
+}
+
+func (b *stripeRefundBackend) Call(_ string, _ string, _ string, params stripe.ParamsContainer, v stripe.LastResponseSetter) error {
+	b.params = append(b.params, params.(*stripe.RefundCreateParams))
+	refund := v.(*stripe.Refund)
+	refund.ID = "re_123"
+	refund.Status = stripe.RefundStatusSucceeded
+	return nil
+}
+
+func (*stripeRefundBackend) CallStreaming(string, string, string, stripe.ParamsContainer, stripe.StreamingLastResponseSetter) error {
+	return nil
+}
+
+func (*stripeRefundBackend) CallRaw(string, string, string, []byte, *stripe.Params, stripe.LastResponseSetter) error {
+	return nil
+}
+
+func (*stripeRefundBackend) CallMultipart(string, string, string, string, *bytes.Buffer, *stripe.Params, stripe.LastResponseSetter) error {
+	return nil
+}
+
+func (*stripeRefundBackend) SetMaxNetworkRetries(int64) {}
+
+func TestStripeRefundUsesStableAmountSpecificIdempotencyKey(t *testing.T) {
+	backend := &stripeRefundBackend{}
+	client := stripe.NewClient("sk_test", stripe.WithBackends(&stripe.Backends{API: backend}))
+	provider := &Stripe{
+		config:      map[string]string{"currency": "CNY"},
+		initialized: true,
+		sc:          client,
+	}
+
+	refund := func(amount string) {
+		_, err := provider.Refund(context.Background(), payment.RefundRequest{
+			TradeNo: "pi_123",
+			OrderID: "sub2_order_456",
+			Amount:  amount,
+		})
+		require.NoError(t, err)
+	}
+
+	refund("12.34")
+	refund("12.34")
+	refund("12.35")
+
+	require.Len(t, backend.params, 3)
+	require.Equal(t, int64(1234), *backend.params[0].Amount)
+	require.Equal(t, "re-sub2_order_456-1234", *backend.params[0].IdempotencyKey)
+	require.Equal(t, backend.params[0].IdempotencyKey, backend.params[1].IdempotencyKey)
+	require.Equal(t, int64(1235), *backend.params[2].Amount)
+	require.Equal(t, "re-sub2_order_456-1235", *backend.params[2].IdempotencyKey)
+	require.NotEqual(t, *backend.params[0].IdempotencyKey, *backend.params[2].IdempotencyKey)
+}