go-cart-actor/pkg/order/stripe.go

package order

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"
)

// StripeProvider implements PaymentProvider against the Stripe REST API using
// PaymentIntents with manual capture (authorize now, capture on fulfillment),
// mirroring the order state machine. It speaks the form-encoded REST API
// directly — no SDK dependency — so it stays in step with the dependency-light
// style of the rest of the module.
//
// Flow mapping:
//   - Authorize -> POST /v1/payment_intents (capture_method=manual, confirm=true)
//   - Capture   -> POST /v1/payment_intents/{id}/capture
//   - Refund    -> POST /v1/refunds (payment_intent={id})
//   - Void      -> POST /v1/payment_intents/{id}/cancel
//
// The authorization reference is the PaymentIntent id (pi_...), which is what
// Capture/Refund/Void operate on.
type StripeProvider struct {
	secretKey string
	baseURL   string // defaults to https://api.stripe.com
	// PaymentMethod is the payment method id/token to confirm with. For a real
	// integration this comes from the client (Stripe.js); for server-side tests
	// and headless flows it can be a test token like "pm_card_visa".
	PaymentMethod string
	client        *http.Client
}

var _ PaymentProvider = (*StripeProvider)(nil)

// NewStripeProvider returns a Stripe-backed provider. baseURL may be empty to
// use the live API; tests pass a fake server URL.
func NewStripeProvider(secretKey, baseURL, paymentMethod string) *StripeProvider {
	if baseURL == "" {
		baseURL = "https://api.stripe.com"
	}
	if paymentMethod == "" {
		paymentMethod = "pm_card_visa" // Stripe test token; override for prod
	}
	return &StripeProvider{
		secretKey:     secretKey,
		baseURL:       strings.TrimSuffix(baseURL, "/"),
		PaymentMethod: paymentMethod,
		client:        &http.Client{Timeout: 20 * time.Second},
	}
}

func (s *StripeProvider) Name() string { return "stripe" }

// post sends a form-encoded request and decodes the JSON response, returning an
// error for any non-2xx (surfacing Stripe's error message).
func (s *StripeProvider) post(ctx context.Context, path string, form url.Values) (map[string]any, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, s.baseURL+path, strings.NewReader(form.Encode()))
	if err != nil {
		return nil, err
	}
	req.SetBasicAuth(s.secretKey, "")
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	resp, err := s.client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	var body map[string]any
	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil {
		return nil, fmt.Errorf("stripe: decode %s: %w", path, err)
	}
	if resp.StatusCode >= 300 {
		return nil, fmt.Errorf("stripe: %s -> %d: %s", path, resp.StatusCode, stripeErr(body))
	}
	return body, nil
}

func stripeErr(body map[string]any) string {
	if e, ok := body["error"].(map[string]any); ok {
		if m, ok := e["message"].(string); ok {
			return m
		}
	}
	return "unknown error"
}

func strField(body map[string]any, key string) string {
	if v, ok := body[key].(string); ok {
		return v
	}
	return ""
}

func (s *StripeProvider) Authorize(ctx context.Context, orderRef string, amount int64, currency string) (Authorization, error) {
	form := url.Values{}
	form.Set("amount", strconv.FormatInt(amount, 10))
	form.Set("currency", strings.ToLower(currency))
	form.Set("capture_method", "manual")
	form.Set("confirm", "true")
	form.Set("payment_method", s.PaymentMethod)
	form.Set("description", "order "+orderRef)
	// Idempotency on the order reference avoids a duplicate intent on retry.
	form.Set("metadata[order_reference]", orderRef)

	body, err := s.post(ctx, "/v1/payment_intents", form)
	if err != nil {
		return Authorization{}, err
	}
	id := strField(body, "id")
	if id == "" {
		return Authorization{}, fmt.Errorf("stripe: authorize returned no payment intent id")
	}
	if status := strField(body, "status"); status != "requires_capture" && status != "succeeded" {
		return Authorization{}, fmt.Errorf("stripe: authorize status %q", status)
	}
	return Authorization{Provider: s.Name(), Reference: id, Amount: amount}, nil
}

func (s *StripeProvider) Capture(ctx context.Context, authRef string, amount int64) (Capture, error) {
	if authRef == "" {
		return Capture{}, fmt.Errorf("stripe: capture requires a payment intent id")
	}
	form := url.Values{}
	if amount > 0 {
		form.Set("amount_to_capture", strconv.FormatInt(amount, 10))
	}
	body, err := s.post(ctx, "/v1/payment_intents/"+url.PathEscape(authRef)+"/capture", form)
	if err != nil {
		return Capture{}, err
	}
	return Capture{Provider: s.Name(), Reference: strField(body, "id"), Amount: amount}, nil
}

func (s *StripeProvider) Refund(ctx context.Context, captureRef string, amount int64) (RefundResult, error) {
	if captureRef == "" {
		return RefundResult{}, fmt.Errorf("stripe: refund requires a payment intent id")
	}
	form := url.Values{}
	form.Set("payment_intent", captureRef)
	if amount > 0 {
		form.Set("amount", strconv.FormatInt(amount, 10))
	}
	body, err := s.post(ctx, "/v1/refunds", form)
	if err != nil {
		return RefundResult{}, err
	}
	return RefundResult{Provider: s.Name(), Reference: strField(body, "id"), Amount: amount}, nil
}

func (s *StripeProvider) Void(ctx context.Context, authRef string) error {
	if authRef == "" {
		return fmt.Errorf("stripe: void requires a payment intent id")
	}
	_, err := s.post(ctx, "/v1/payment_intents/"+url.PathEscape(authRef)+"/cancel", url.Values{})
	return err
}