feat(backend): implement notification system (logger mock)

backend/internal/notifications/service.go

@@ -0,0 +1,37 @@
+package notifications
+
+import (
+	"context"
+	"log"
+
+	"github.com/saveinmed/backend-go/internal/domain"
+)
+
+// NotificationService defines the contract for sending alerts.
+type NotificationService interface {
+	NotifyOrderCreated(ctx context.Context, order *domain.Order, buyer, seller *domain.User) error
+	NotifyOrderStatusChanged(ctx context.Context, order *domain.Order, buyer *domain.User) error
+}
+
+// LoggerNotificationService prints notifications to stdout for dev/MVP.
+type LoggerNotificationService struct{}
+
+func NewLoggerNotificationService() *LoggerNotificationService {
+	return &LoggerNotificationService{}
+}
+
+func (s *LoggerNotificationService) NotifyOrderCreated(ctx context.Context, order *domain.Order, buyer, seller *domain.User) error {
+	log.Printf("📧 [EMAIL] To: Seller <%s>\n   Subject: Novo Pedido #%s recebido!\n   Body: Olá %s, você recebeu um novo pedido de %s. Total: R$ %.2f",
+		seller.Email, order.ID, seller.Name, buyer.Name, float64(order.TotalCents)/100)
+
+	log.Printf("📧 [EMAIL] To: Buyer <%s>\n   Subject: Pedido #%s confirmado!\n   Body: Olá %s, seu pedido foi recebido e está aguardando processamento.",
+		buyer.Email, order.ID, buyer.Name)
+
+	return nil
+}
+
+func (s *LoggerNotificationService) NotifyOrderStatusChanged(ctx context.Context, order *domain.Order, buyer *domain.User) error {
+	log.Printf("📧 [EMAIL] To: Buyer <%s>\n   Subject: Atualização do Pedido #%s\n   Body: Olá %s, seu pedido mudou para status: %s.",
+		buyer.Email, order.ID, buyer.Name, order.Status)
+	return nil
+}

backend/internal/server/server.go

@@ -15,6 +15,7 @@ import (
 	"github.com/saveinmed/backend-go/internal/domain"
 	"github.com/saveinmed/backend-go/internal/http/handler"
 	"github.com/saveinmed/backend-go/internal/http/middleware"
+	"github.com/saveinmed/backend-go/internal/notifications"
 	"github.com/saveinmed/backend-go/internal/payments"
 	"github.com/saveinmed/backend-go/internal/repository/postgres"
 	"github.com/saveinmed/backend-go/internal/usecase"
@@ -34,9 +35,11 @@ func New(cfg config.Config) (*Server, error) {
 		return nil, err
 	}
 
-	repo := postgres.New(db)
+	repoInstance := postgres.New(db)
-	gateway := payments.NewMercadoPagoGateway(cfg.MercadoPagoBaseURL, cfg.MarketplaceCommission)
+	paymentGateway := payments.NewMercadoPagoGateway(cfg.MercadoPagoBaseURL, cfg.MarketplaceCommission)
-	svc := usecase.NewService(repo, gateway, cfg.MarketplaceCommission, cfg.JWTSecret, cfg.JWTExpiresIn, cfg.PasswordPepper)
+	// Services
+	notifySvc := notifications.NewLoggerNotificationService()
+	svc := usecase.NewService(repoInstance, paymentGateway, notifySvc, cfg.MarketplaceCommission, cfg.JWTSecret, cfg.JWTExpiresIn, cfg.PasswordPepper)
 	h := handler.New(svc, cfg.BuyerFeeRate)
 
 	mux := http.NewServeMux()

backend/internal/usecase/usecase.go

@@ -13,6 +13,7 @@ import (
 	"github.com/gofrs/uuid/v5"
 
 	"github.com/saveinmed/backend-go/internal/domain"
+	"github.com/saveinmed/backend-go/internal/notifications"
 )
 
 // Repository defines DB contract for the core entities.
@@ -72,6 +73,7 @@ type PaymentGateway interface {
 type Service struct {
 	repo                  Repository
 	pay                   PaymentGateway
+	notify                notifications.NotificationService
 	jwtSecret             []byte
 	tokenTTL              time.Duration
 	marketplaceCommission float64
@@ -83,10 +85,11 @@ const (
 )
 
 // NewService wires use cases together.
-func NewService(repo Repository, pay PaymentGateway, commissionPct float64, jwtSecret string, tokenTTL time.Duration, passwordPepper string) *Service {
+func NewService(repo Repository, pay PaymentGateway, notify notifications.NotificationService, commissionPct float64, jwtSecret string, tokenTTL time.Duration, passwordPepper string) *Service {
 	return &Service{
 		repo:                  repo,
 		pay:                   pay,
+		notify:                notify,
 		jwtSecret:             []byte(jwtSecret),
 		tokenTTL:              tokenTTL,
 		marketplaceCommission: commissionPct,
@@ -313,7 +316,33 @@ func (s *Service) AdjustInventory(ctx context.Context, productID uuid.UUID, delt
 func (s *Service) CreateOrder(ctx context.Context, order *domain.Order) error {
 	order.ID = uuid.Must(uuid.NewV7())
 	order.Status = domain.OrderStatusPending
-	return s.repo.CreateOrder(ctx, order)
+
+	if err := s.repo.CreateOrder(ctx, order); err != nil {
+		return err
+	}
+
+	// Async notification (ignore errors to not block request)
+	go func() {
+		// Fetch buyer details
+		buyer, err := s.repo.GetUser(context.Background(), order.BuyerID)
+		if err != nil {
+			return
+		}
+
+		// Fetch seller details (hack: get list and pick first for MVP)
+		users, _, _ := s.repo.ListUsers(context.Background(), domain.UserFilter{CompanyID: &order.SellerID, Limit: 1})
+		var seller *domain.User
+		if len(users) > 0 {
+			seller = &users[0]
+		} else {
+			// Fallback mock
+			seller = &domain.User{Name: "Seller", Email: "seller@platform.com"}
+		}
+
+		s.notify.NotifyOrderCreated(context.Background(), order, buyer, seller)
+	}()
+
+	return nil
 }
 
 func (s *Service) ListOrders(ctx context.Context, filter domain.OrderFilter, page, pageSize int) (*domain.OrderPage, error) {
@@ -368,7 +397,28 @@ func (s *Service) UpdateOrderStatus(ctx context.Context, id uuid.UUID, status do
 		return errors.New("order is in terminal state")
 	}
 
-	return s.repo.UpdateOrderStatus(ctx, id, status)
+	if err := s.repo.UpdateOrderStatus(ctx, id, status); err != nil {
+		return err
+	}
+
+	// Async notification
+	go func() {
+		// Re-fetch order to get all details if necessary, but we have fields.
+		// Need buyer to send email
+		updatedOrder, _ := s.repo.GetOrder(context.Background(), id)
+		if updatedOrder == nil {
+			return
+		}
+
+		buyer, err := s.repo.GetUser(context.Background(), updatedOrder.BuyerID)
+		if err != nil {
+			return
+		}
+
+		s.notify.NotifyOrderStatusChanged(context.Background(), updatedOrder, buyer)
+	}()
+
+	return nil
 }
 
 func (s *Service) DeleteOrder(ctx context.Context, id uuid.UUID) error {

backend/internal/usecase/usecase_test.go

@@ -329,11 +329,22 @@ func (m *MockPaymentGateway) CreatePreference(ctx context.Context, order *domain
 	}, nil
 }
 
+// MockNotificationService for testing
+type MockNotificationService struct{}
+
+func (m *MockNotificationService) NotifyOrderCreated(ctx context.Context, order *domain.Order, buyer, seller *domain.User) error {
+	return nil
+}
+func (m *MockNotificationService) NotifyOrderStatusChanged(ctx context.Context, order *domain.Order, buyer *domain.User) error {
+	return nil
+}
+
 // Helper to create a test service
 func newTestService() (*Service, *MockRepository) {
 	repo := NewMockRepository()
 	gateway := &MockPaymentGateway{}
-	svc := NewService(repo, gateway, 2.5, "test-secret", time.Hour, "test-pepper")
+	notify := &MockNotificationService{}
+	svc := NewService(repo, gateway, notify, 2.5, "test-secret", time.Hour, "test-pepper")
 	return svc, repo
 }