feat(loyalty): one-time EnakPoint payment code
Adds POST /customer/wallet/payment-code (docs/prd-point-coin.md F9, K8, PC-304). The customer approves with their PIN on their own phone and gets a 6-digit code, as digits and as a QR payload (enakpoint:<code>) for the app to render, valid for two minutes. The PIN is never typed at the cashier. Codes are drawn from crypto/rand and stored in Redis with SET NX and a TTL, bound to the customer; a new code retires the previous one. Redeeming is a single Lua step that uses the code up only if it belongs to the order's customer, so it stays one-time under a race, and a cashier scanning it against the wrong order does not burn it for its owner, which a plain GETDEL would. Expired, used, unknown and other customers' codes are all refused alike. Tests run against miniredis, added as a test dependency. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
efrilm
co-authored by
Claude Opus 5.5
Claude Opus 5.5
parent
cf5332c281
commit
0c4dd72583
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package processor
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import (
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"context"
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"crypto/rand"
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"errors"
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"fmt"
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"math/big"
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"strings"
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"time"
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"github.com/google/uuid"
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"apskel-pos-be/internal/models"
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"apskel-pos-be/internal/repository"
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)
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const (
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paymentCodeDigits = 6
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paymentCodeTTL = 2 * time.Minute
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paymentCodeAttempts = 5
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// PaymentCodeQRPrefix marks a scanned QR as an EnakPoint payment code.
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PaymentCodeQRPrefix = "enakpoint:"
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)
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// ErrPaymentCodeInvalid means the code was never issued, has expired, has been used,
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// or belongs to another customer.
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var ErrPaymentCodeInvalid = errors.New("payment code is invalid or expired")
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type pinVerifier interface {
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VerifyPin(ctx context.Context, customerID uuid.UUID, pin string, action PinAction, info models.CustomerPinRequestInfo) error
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}
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// PaymentCodeProcessor issues and redeems the one-time codes that let a cashier take a
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// customer's EnakPoint (docs/prd-point-coin.md F9, K8). The customer approves with
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// their PIN on their own phone and shows the code; the PIN is never typed on the
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// cashier's device.
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type PaymentCodeProcessor struct {
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codes repository.PaymentCodeRepository
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pins pinVerifier
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now func() time.Time
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}
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func NewPaymentCodeProcessor(codes repository.PaymentCodeRepository, pins pinVerifier) *PaymentCodeProcessor {
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return &PaymentCodeProcessor{codes: codes, pins: pins, now: time.Now}
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}
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// Issue checks the customer's PIN and returns a fresh 6-digit code, valid for two
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// minutes and bound to the customer. A new code retires the previous one.
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func (p *PaymentCodeProcessor) Issue(ctx context.Context, customerID uuid.UUID, pin string, info models.CustomerPinRequestInfo) (*models.PaymentCode, error) {
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if err := p.pins.VerifyPin(ctx, customerID, pin, PinActionPay, info); err != nil {
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return nil, err
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}
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for attempt := 0; attempt < paymentCodeAttempts; attempt++ {
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code, err := randomDigits(paymentCodeDigits)
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if err != nil {
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return nil, err
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}
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err = p.codes.Save(ctx, code, customerID, paymentCodeTTL)
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if errors.Is(err, repository.ErrPaymentCodeTaken) {
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continue
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}
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if err != nil {
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return nil, err
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}
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return &models.PaymentCode{
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Code: code,
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QRPayload: PaymentCodeQRPrefix + code,
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ExpiresAt: p.now().Add(paymentCodeTTL),
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}, nil
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}
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return nil, fmt.Errorf("could not draw a free payment code after %d attempts", paymentCodeAttempts)
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}
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// Redeem uses a code up for a payment by the given customer. It accepts the code as
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// typed or as scanned from the QR. Every failure is ErrPaymentCodeInvalid.
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func (p *PaymentCodeProcessor) Redeem(ctx context.Context, code string, customerID uuid.UUID) error {
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code = strings.TrimPrefix(strings.TrimSpace(code), PaymentCodeQRPrefix)
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if len(code) != paymentCodeDigits {
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return ErrPaymentCodeInvalid
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}
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err := p.codes.Consume(ctx, code, customerID)
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if errors.Is(err, repository.ErrPaymentCodeNotFound) || errors.Is(err, repository.ErrPaymentCodeWrongCustomer) {
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return ErrPaymentCodeInvalid
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}
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return err
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}
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// randomDigits draws n decimal digits from a cryptographic source, so codes cannot be
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// predicted.
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func randomDigits(n int) (string, error) {
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var b strings.Builder
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for i := 0; i < n; i++ {
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d, err := rand.Int(rand.Reader, big.NewInt(10))
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if err != nil {
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return "", fmt.Errorf("failed to draw a payment code: %w", err)
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}
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b.WriteByte(byte('0' + d.Int64()))
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}
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return b.String(), nil
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}
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@@ -0,0 +1,136 @@
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package processor
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import (
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"context"
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"sync"
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"sync/atomic"
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"testing"
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"time"
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"github.com/alicebob/miniredis/v2"
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"github.com/google/uuid"
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"github.com/redis/go-redis/v9"
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"github.com/stretchr/testify/assert"
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"github.com/stretchr/testify/require"
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"apskel-pos-be/internal/models"
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"apskel-pos-be/internal/repository"
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)
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type pinVerifierFake struct{ good string }
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func (f pinVerifierFake) VerifyPin(_ context.Context, _ uuid.UUID, pin string, action PinAction, _ models.CustomerPinRequestInfo) error {
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if action != PinActionPay {
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return &PinError{Code: "UNEXPECTED_ACTION"}
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}
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if pin != f.good {
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return &PinError{Code: PinErrInvalid, RemainingAttempts: 4}
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}
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return nil
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}
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func newPaymentCodeTest(t *testing.T) (*PaymentCodeProcessor, *miniredis.Miniredis) {
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t.Helper()
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mr := miniredis.RunT(t)
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client := redis.NewClient(&redis.Options{Addr: mr.Addr()})
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t.Cleanup(func() { client.Close() })
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return NewPaymentCodeProcessor(repository.NewPaymentCodeRepository(client), pinVerifierFake{good: "482913"}), mr
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}
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func TestPaymentCode_IssueNeedsThePin(t *testing.T) {
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p, mr := newPaymentCodeTest(t)
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_, err := p.Issue(context.Background(), uuid.New(), "000000", models.CustomerPinRequestInfo{})
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var pe *PinError
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require.ErrorAs(t, err, &pe)
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assert.Equal(t, PinErrInvalid, pe.Code)
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assert.Empty(t, mr.Keys(), "nothing is issued without the PIN")
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}
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func TestPaymentCode_Lifecycle(t *testing.T) {
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p, mr := newPaymentCodeTest(t)
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ctx := context.Background()
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customer, other := uuid.New(), uuid.New()
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code, err := p.Issue(ctx, customer, "482913", models.CustomerPinRequestInfo{})
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require.NoError(t, err)
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assert.Len(t, code.Code, 6)
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assert.Equal(t, "enakpoint:"+code.Code, code.QRPayload)
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assert.WithinDuration(t, time.Now().Add(2*time.Minute), code.ExpiresAt, 2*time.Second)
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assert.InDelta(t, 120, mr.TTL("wallet:paycode:"+code.Code).Seconds(), 1, "Redis expires it by itself")
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// A code of another customer is refused, and stays usable by its owner.
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assert.ErrorIs(t, p.Redeem(ctx, code.Code, other), ErrPaymentCodeInvalid)
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// Scanned from the QR it works; used once, it is gone.
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require.NoError(t, p.Redeem(ctx, code.QRPayload, customer))
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assert.ErrorIs(t, p.Redeem(ctx, code.Code, customer), ErrPaymentCodeInvalid)
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// An expired code is refused.
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late, err := p.Issue(ctx, customer, "482913", models.CustomerPinRequestInfo{})
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require.NoError(t, err)
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mr.FastForward(2*time.Minute + time.Second)
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assert.ErrorIs(t, p.Redeem(ctx, late.Code, customer), ErrPaymentCodeInvalid)
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// A new code retires the previous one.
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first, err := p.Issue(ctx, customer, "482913", models.CustomerPinRequestInfo{})
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require.NoError(t, err)
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second, err := p.Issue(ctx, customer, "482913", models.CustomerPinRequestInfo{})
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require.NoError(t, err)
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if first.Code != second.Code {
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assert.ErrorIs(t, p.Redeem(ctx, first.Code, customer), ErrPaymentCodeInvalid)
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}
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require.NoError(t, p.Redeem(ctx, second.Code, customer))
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// Garbage is refused without touching Redis.
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for _, bad := range []string{"", "12345", "1234567", "enakpoint:"} {
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assert.ErrorIs(t, p.Redeem(ctx, bad, customer), ErrPaymentCodeInvalid, bad)
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}
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}
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// Two cashiers scanning the same code at once: exactly one gets it.
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func TestPaymentCode_UsedOnceUnderRace(t *testing.T) {
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p, _ := newPaymentCodeTest(t)
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ctx := context.Background()
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customer := uuid.New()
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code, err := p.Issue(ctx, customer, "482913", models.CustomerPinRequestInfo{})
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require.NoError(t, err)
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var wins int32
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var wg sync.WaitGroup
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for i := 0; i < 20; i++ {
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wg.Add(1)
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go func() {
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defer wg.Done()
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if p.Redeem(ctx, code.Code, customer) == nil {
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atomic.AddInt32(&wins, 1)
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}
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}()
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}
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wg.Wait()
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assert.Equal(t, int32(1), wins)
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}
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func TestPaymentCode_SaveRefusesALiveCode(t *testing.T) {
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mr := miniredis.RunT(t)
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client := redis.NewClient(&redis.Options{Addr: mr.Addr()})
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defer client.Close()
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repo := repository.NewPaymentCodeRepository(client)
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ctx := context.Background()
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require.NoError(t, repo.Save(ctx, "123456", uuid.New(), time.Minute))
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assert.ErrorIs(t, repo.Save(ctx, "123456", uuid.New(), time.Minute), repository.ErrPaymentCodeTaken,
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"a live code is never handed to a second customer")
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}
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func TestRandomDigits(t *testing.T) {
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seen := map[string]bool{}
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for i := 0; i < 200; i++ {
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d, err := randomDigits(6)
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require.NoError(t, err)
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require.Len(t, d, 6)
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for _, r := range d {
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require.True(t, r >= '0' && r <= '9')
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}
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seen[d] = true
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}
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assert.Greater(t, len(seen), 190, "codes do not repeat")
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}
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