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
+}