Added analytics by transactions

backend/src/api/services/transactions.go

@@ -13,6 +13,7 @@ type TransactionService interface {
 	Create(ctx context.Context, req domain.CreateTransactionRequest) (*domain.Transaction, error)
 	GetByID(ctx context.Context, id int64) (*domain.Transaction, error)
 	List(ctx context.Context, filter domain.TransactionListFilter) ([]*domain.Transaction, error)
+	Analytics(ctx context.Context, filter domain.TransactionAnalyticsFilter) (domain.TransactionAnalytics, error)
 	Update(ctx context.Context, id int64, req domain.UpdateTransactionRequest) (*domain.Transaction, error)
 	Delete(ctx context.Context, id int64) error
 }
@@ -31,6 +32,7 @@ var (
 	ErrReceiptLinkConflict = errors.New("receipt_id and detach_receipt cannot be used together")
 	ErrInvalidTransaction  = errors.New("type and category are required")
 	ErrReceiptNotFound     = errors.New("receipt not found")
+	ErrInvalidAnalytics    = errors.New("type must be income or expense")
 )
 
 func (s *transactionService) Create(ctx context.Context, req domain.CreateTransactionRequest) (*domain.Transaction, error) {
@@ -85,6 +87,18 @@ func (s *transactionService) List(ctx context.Context, filter domain.Transaction
 	return s.repo.List(ctx, filter)
 }
 
+func (s *transactionService) Analytics(ctx context.Context, filter domain.TransactionAnalyticsFilter) (domain.TransactionAnalytics, error) {
+	if filter.Type != nil {
+		typeValue := strings.TrimSpace(*filter.Type)
+		if typeValue != "income" && typeValue != "expense" {
+			return domain.TransactionAnalytics{}, ErrInvalidAnalytics
+		}
+		filter.Type = &typeValue
+	}
+
+	return s.repo.Analytics(ctx, filter)
+}
+
 func (s *transactionService) Update(ctx context.Context, id int64, req domain.UpdateTransactionRequest) (*domain.Transaction, error) {
 	if req.ReceiptID != nil && req.DetachReceipt {
 		return nil, ErrReceiptLinkConflict