add add user to budget route

internal/services/budget/budget_service.go

@@ -50,13 +50,9 @@ func (s *BudgetService) AddBudget(ctx context.Context, budget *BudgetEntity) (*B
 		return nil, fmt.Errorf("unable to insert row: %w", err)
 	}
 
-	query = `INSERT INTO users_budgets (user_id, budget_id) VALUES (@user_id, @budget_id) RETURNING id`
-	args = pgx.NamedArgs{
-		"user_id":   userId,
-		"budget_id": budget.Id,
-	}
-	if err := s.db.QueryRow(ctx, query, args).Scan(&budget.Id); err != nil {
-		return nil, fmt.Errorf("unable to insert row: %w", err)
+	_, err = s.AddUserToBudget(ctx, budget.Id, userId)
+	if err != nil {
+		return nil, err
 	}
 
 	if err = tx.Commit(ctx); err != nil {
@@ -92,3 +88,20 @@ func (s *BudgetService) GetBudgets(ctx context.Context) ([]*BudgetEntity, error)
 
 	return budgets, nil
 }
+
+func (s *BudgetService) AddUserToBudget(
+	ctx context.Context,
+	budgetId int,
+	userId int,
+) (int, error) {
+	query := `INSERT INTO users_budgets (user_id, budget_id) VALUES (@user_id, @budget_id) RETURNING id`
+	args := pgx.NamedArgs{
+		"user_id":   userId,
+		"budget_id": budgetId,
+	}
+	id := 0
+	if err := s.db.QueryRow(ctx, query, args).Scan(&id); err != nil {
+		return 0, fmt.Errorf("unable to insert row: %w", err)
+	}
+	return id, nil
+}