add create budget route

internal/services/budget/budget_service.go

@@ -0,0 +1,66 @@
+package budget
+
+import (
+	"context"
+	"fmt"
+
+	"git.3crabs.ru/save_my_money/smm_core/internal/services/context_utils"
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+type BudgetEntity struct {
+	Id           int
+	Name         string
+	StartDay     int
+	MonthlyLimit int
+}
+
+type BudgetService struct {
+	db *pgxpool.Pool
+}
+
+func NewBudgetService(
+	db *pgxpool.Pool,
+) *BudgetService {
+	return &BudgetService{
+		db: db,
+	}
+}
+
+func (s *BudgetService) AddBudget(ctx context.Context, budget *BudgetEntity) (*BudgetEntity, error) {
+	userId, err := context_utils.GetUserId(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	tx, err := s.db.Begin(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback(ctx)
+
+	query := `INSERT INTO budgets (name, start_day, monthly_limit) VALUES (@name, @start_day, @monthly_limit) RETURNING id`
+	args := pgx.NamedArgs{
+		"name":          budget.Name,
+		"start_day":     budget.StartDay,
+		"monthly_limit": budget.MonthlyLimit,
+	}
+	if err := s.db.QueryRow(ctx, query, args).Scan(&budget.Id); err != nil {
+		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)
+	}
+
+	if err = tx.Commit(ctx); err != nil {
+		return nil, err
+	}
+	return budget, nil
+}