timer

function displayTime(time)
    minutes = 0
    while time >= 60 do
        time = time-60
        minutes = minutes + 1
    end
    seconds = time
    if minutes < 10 then
        minutes = "0"..tostring(minutes)
    else
        minutes = tostring(minutes)
    end
    if seconds < 10 then
        seconds = "0"..tostring(seconds)
    else
        seconds = tostring(seconds)
    end
    return minutes..":"..seconds
end

timer = 1200
monitor_1 = peripheral.wrap("back")
monitor_2 = peripheral.wrap("monitor_0")
monitor_1.setTextScale(5)
monitor_2.setTextScale(5)
xSize, ySize = monitor_1.getSize()
while true do
    if timer < 0 then
        monitor_1.setBackgroundColor(colors.white)
        monitor_2.setBackgroundColor(colors.white)
        monitor_1.setTextColor(colors.black)
        monitor_2.setTextColor(colors.black)
        text = "Time!"
    else
        text = displayTime(timer)
    end
    monitor_1.clear()
    monitor_2.clear()
    monitor_1.setCursorPos(xSize/2-(string.len(text)/2)+1,ySize/2+1)
    monitor_2.setCursorPos(xSize/2-(string.len(text)/2)+1,ySize/2+1)
    monitor_1.write(text)
    monitor_2.write(text)
    timer = timer - 1
    sleep(1)
    if timer < -1 then
        os.pullEvent("key")
        monitor_1.setBackgroundColor(colors.black)
        monitor_2.setBackgroundColor(colors.black)
        monitor_1.setTextColor(colors.white)
        monitor_2.setTextColor(colors.white)
        monitor_1.clear()
        monitor_2.clear()
        break
    end
end