private void btn_signin_Click(object sender, EventArgs e)
        {
            if (password.Text == "")
            {
                MessageBox.Show("Please provide password!");
            }
            else
            {
                Staff member = service.DoLogin(Convert.ToInt32(Cmb_Username.SelectedValue), password.Text);

                if (member is null)
                {
                    MessageBox.Show("invalid username or password!");
                }
                else
                {
                    this.Hide();
                    switch (member.Role)
                    {
                    case Staff_Type.Bartender:
                        new KitchenBar(Staff_Type.Bartender).ShowDialog();
                        //this.Close();
                        break;

                    case Staff_Type.Chef:
                        new KitchenBar(Staff_Type.Chef).ShowDialog();
                        //this.Close();
                        break;

                    case Staff_Type.Waiter:
                        new TableView(member).ShowDialog();
                        //this.Close();
                        break;

                    case Staff_Type.Manager:
                    default:
                        new Overview(member).ShowDialog();
                        //this.Close();
                        break;
                    }
                    this.Close();
                }
            }
        }