Trading-City Mobfarm-Ghast

mon = peripheral.wrap("back")
mon.setTextScale(4.5)

function calc_color(color)
    return math.pow(2, color - 1)
end

function msg(gap, line, color, groundb, text)
    mon.setBackgroundColor(calc_color(groundb))
    mon.setCursorPos(gap,line)
    mon.setTextColor(calc_color(color))
    text = mon.write(text)
end

function clear()
    for a = 1,10 do
        msg(01,a,16,16,"                              ")
    end
end

while true do
  if rs.getInput("top", true) then
    clear()
    msg(03,02,09,16,"Mobfarm")
    msg(11,02,06,16,"OPEN")
  else
    clear()
    msg(02,02,09,16,"Mobfarm")
    msg(10,02,15,16,"CLOSED")
  end
  sleep(10)
end