feat(service): add card conversion service

backend/internal/service/card_service.go

@@ -0,0 +1,38 @@
+package service
+
+import (
+	"context"
+	"fmt"
+
+	"card-to-iban/internal/card"
+)
+
+type CardToIBANClient interface {
+	Convert(ctx context.Context, cardNumber string) (string, error)
+}
+
+type CardService struct {
+	client CardToIBANClient
+}
+
+func NewCardService(client CardToIBANClient) *CardService {
+	return &CardService{
+		client: client,
+	}
+}
+
+func (s *CardService) ConvertCardToIBAN(
+	ctx context.Context,
+	cardNumber string,
+) (string, error) {
+	if err := card.Validate(cardNumber); err != nil {
+		return "", err
+	}
+
+	iban, err := s.client.Convert(ctx, cardNumber)
+	if err != nil {
+		return "", fmt.Errorf("convert card to iban: %w", err)
+	}
+
+	return iban, nil
+}

backend/internal/service/card_service_test.go

@@ -0,0 +1,135 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+type fakeCardToIBANClient struct {
+	iban            string
+	err             error
+	called          bool
+	receivedCard    string
+	receivedContext context.Context
+}
+
+func (f *fakeCardToIBANClient) Convert(
+	ctx context.Context,
+	cardNumber string,
+) (string, error) {
+	f.called = true
+	f.receivedCard = cardNumber
+	f.receivedContext = ctx
+
+	return f.iban, f.err
+}
+
+func TestCardServiceConvertCardToIBANSuccess(t *testing.T) {
+	client := &fakeCardToIBANClient{
+		iban: "IR123456789012345678901234",
+	}
+
+	service := NewCardService(client)
+
+	cardNumber := "6037991234567890"
+
+	iban, err := service.ConvertCardToIBAN(
+		context.Background(),
+		cardNumber,
+	)
+
+	if err != nil {
+		t.Fatalf("ConvertCardToIBAN() unexpected error: %v", err)
+	}
+
+	if iban != client.iban {
+		t.Errorf(
+			"ConvertCardToIBAN() iban = %q, want %q",
+			iban,
+			client.iban,
+		)
+	}
+
+	if !client.called {
+		t.Error("expected client to be called")
+	}
+
+	if client.receivedCard != cardNumber {
+		t.Errorf(
+			"client received card = %q, want %q",
+			client.receivedCard,
+			cardNumber,
+		)
+	}
+}
+
+func TestCardServiceRejectsInvalidCardBeforeClientCall(t *testing.T) {
+	client := &fakeCardToIBANClient{}
+
+	service := NewCardService(client)
+
+	_, err := service.ConvertCardToIBAN(
+		context.Background(),
+		"123",
+	)
+
+	if err == nil {
+		t.Fatal("expected validation error")
+	}
+
+	if client.called {
+		t.Error("client should not be called for an invalid card")
+	}
+}
+
+func TestCardServiceReturnsClientError(t *testing.T) {
+	clientErr := errors.New("upstream unavailable")
+
+	client := &fakeCardToIBANClient{
+		err: clientErr,
+	}
+
+	service := NewCardService(client)
+
+	_, err := service.ConvertCardToIBAN(
+		context.Background(),
+		"6037991234567890",
+	)
+
+	if err == nil {
+		t.Fatal("expected client error")
+	}
+
+	if !errors.Is(err, clientErr) {
+		t.Errorf(
+			"ConvertCardToIBAN() error = %v, want wrapped %v",
+			err,
+			clientErr,
+		)
+	}
+}
+
+func TestCardServicePassesContextToClient(t *testing.T) {
+	client := &fakeCardToIBANClient{
+		iban: "IR123456789012345678901234",
+	}
+
+	service := NewCardService(client)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	_, err := service.ConvertCardToIBAN(
+		ctx,
+		"6037991234567890",
+	)
+
+	if err != nil {
+		t.Fatalf("ConvertCardToIBAN() unexpected error: %v", err)
+	}
+
+	if client.receivedContext != ctx {
+		t.Error("service did not pass the request context to the client")
+	}
+}