public Boolean isValid(string username, string password)
        {
            List <Staff> staffs = staffDAO.getAllStaffs();

            foreach (Staff staff in staffs)
            {
                if (staff.Name.Equals(username) && PasswrodHash.ValidatePassword(password, staff.Password))
                {
                    roleID = staff.Role;
                    return(true);
                }
            }
            return(false);
        }
        public void addStaff(string username, string password, long role)
        {
            string hashedPassword = PasswrodHash.HashPassword(password);

            staffDAO.addStaff(username, hashedPassword, role);
        }