private void btnRemove_Click(object sender, EventArgs e)
        {
            var confirmResult = MessageBox.Show("Are you sure to delete this user?",
                                                "Confirm",
                                                MessageBoxButtons.YesNo);

            if (confirmResult == DialogResult.Yes)
            {
                switch (user.Role)
                {
                case "Worker":
                    Worker worker = Worker.GetByUserId(user.Id);
                    worker.Delete(dpEndDate.Value);
                    break;

                case "Supervisor":
                    Supervisor supervisor = Supervisor.GetByUserId(user.Id);
                    supervisor.Delete(dpEndDate.Value);
                    break;

                case "Administrator":
                    Administrator admin = Administrator.GetByUserId(user.Id);
                    admin.Delete(dpEndDate.Value);
                    break;

                case "Manager":
                    Manager manager = Manager.GetByUserId(user.Id);
                    manager.Delete(dpEndDate.Value);
                    break;
                }

                mainForm.ShowUsers(User.GetAll());
                this.Close();
            }
        }