1 files changed, 124 insertions, 0 deletions
diff --git a/internal/billing/stripe_preflight.go b/internal/billing/stripe_preflight.go
new file mode 100644
index 0000000..4f9250c
--- /dev/null
+++ b/internal/billing/stripe_preflight.go
@@ -0,0 +1,124 @@
+package billing
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/stripe/stripe-go/v86"
+)
+
+const (
+	stripeAPIBaseURL       = "https://api.stripe.com"
+	maxStripeErrorBodySize = 64 << 10
+)
+
+var ErrLiveStripeKey = errors.New("Stripe permission preflight only accepts test-mode keys")
+
+type StripePermissionCheck struct {
+	Name       string `json:"name"`
+	OK         bool   `json:"ok"`
+	StatusCode int    `json:"status_code"`
+	ErrorCode  string `json:"error_code,omitempty"`
+	ErrorType  string `json:"error_type,omitempty"`
+}
+
+type StripePreflightResult struct {
+	APIVersion string                  `json:"api_version"`
+	TestMode   bool                    `json:"test_mode"`
+	Ready      bool                    `json:"ready"`
+	Checks     []StripePermissionCheck `json:"checks"`
+}
+
+type stripeReadCheck struct {
+	name string
+	path string
+}
+
+var stripeRequiredReadChecks = []stripeReadCheck{
+	{name: "customers_read", path: "/v1/customers"},
+	{name: "checkout_sessions_read", path: "/v1/checkout/sessions"},
+	{name: "setup_intents_read", path: "/v1/setup_intents"},
+	{name: "payment_intents_read", path: "/v1/payment_intents"},
+	{name: "refunds_read", path: "/v1/refunds"},
+	{name: "charges_read", path: "/v1/charges"},
+	{name: "disputes_read", path: "/v1/disputes"},
+	{name: "invoices_read", path: "/v1/invoices"},
+	{name: "billing_portal_configurations_read", path: "/v1/billing_portal/configurations"},
+}
+
+// CheckStripePermissions validates the read side of the restricted-key contract
+// without creating Stripe objects. Write permissions are exercised by the
+// sandbox Checkout, Portal, automatic top-up, refund, and reconciliation flows.
+func CheckStripePermissions(ctx context.Context, apiKey string) (StripePreflightResult, error) {
+	return checkStripePermissions(ctx, apiKey, stripeAPIBaseURL, http.DefaultClient)
+}
+
+func checkStripePermissions(ctx context.Context, apiKey, baseURL string, client *http.Client) (StripePreflightResult, error) {
+	apiKey = strings.TrimSpace(apiKey)
+	result := StripePreflightResult{
+		APIVersion: stripe.APIVersion,
+		TestMode:   isStripeTestKey(apiKey),
+		Checks:     make([]StripePermissionCheck, 0, len(stripeRequiredReadChecks)),
+	}
+	if !result.TestMode {
+		return result, ErrLiveStripeKey
+	}
+	result.Ready = true
+	if client == nil {
+		client = http.DefaultClient
+	}
+	for _, check := range stripeRequiredReadChecks {
+		item := runStripeReadCheck(ctx, client, apiKey, baseURL, check)
+		result.Checks = append(result.Checks, item)
+		result.Ready = result.Ready && item.OK
+	}
+	return result, nil
+}
+
+func runStripeReadCheck(ctx context.Context, client *http.Client, apiKey, baseURL string, check stripeReadCheck) StripePermissionCheck {
+	endpoint, err := url.JoinPath(baseURL, check.path)
+	if err != nil {
+		return StripePermissionCheck{Name: check.name, ErrorType: "configuration_error"}
+	}
+	query := url.Values{"limit": []string{"1"}}
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint+"?"+query.Encode(), nil)
+	if err != nil {
+		return StripePermissionCheck{Name: check.name, ErrorType: "configuration_error"}
+	}
+	request.Header.Set("Authorization", "Bearer "+apiKey)
+	request.Header.Set("Stripe-Version", stripe.APIVersion)
+	response, err := client.Do(request)
+	if err != nil {
+		return StripePermissionCheck{Name: check.name, ErrorType: "network_error"}
+	}
+	defer response.Body.Close()
+	item := StripePermissionCheck{Name: check.name, OK: response.StatusCode >= 200 && response.StatusCode < 300, StatusCode: response.StatusCode}
+	if item.OK {
+		_, _ = io.Copy(io.Discard, response.Body)
+		return item
+	}
+	var envelope struct {
+		Error struct {
+			Code string `json:"code"`
+			Type string `json:"type"`
+		} `json:"error"`
+	}
+	if err := json.NewDecoder(io.LimitReader(response.Body, maxStripeErrorBodySize)).Decode(&envelope); err == nil {
+		item.ErrorCode = envelope.Error.Code
+		item.ErrorType = envelope.Error.Type
+	}
+	if item.ErrorType == "" {
+		item.ErrorType = fmt.Sprintf("http_%d", response.StatusCode)
+	}
+	return item
+}
+
+func isStripeTestKey(value string) bool {
+	return strings.HasPrefix(value, "rk_test_") || strings.HasPrefix(value, "sk_test_")
+}