timer

local mon = peripheral.find("monitor")
mon.setTextScale(2)

local mW, mH = mon.getSize()

local args = {...}
local mins = 0
local seconds = 0

if #args == 0 then
  printError("Syntax: timer [minutes] <seconds>")
  return
elseif #args == 1 then
  seconds = tonumber(args[1])
else
  mins = tonumber(args[1])
  seconds = tonumber(args[2])
end

if seconds > 59 then
  mins = mins + math.floor(seconds / 60)
  seconds = seconds % 60
end

seconds = seconds + 1

local startEpoch = os.epoch("utc") / 1000
local lastFire = -1
while mins > 0 or seconds > 0 do
  local time = math.floor(os.epoch("utc") / 1000 - startEpoch)
  if time > lastFire then
    lastFire = time

    seconds = seconds - 1
    if seconds == -1 then
      seconds = 59
      mins = mins - 1
    end


    mon.clear()

    local str = mins .. ":" .. string.format("%1.2d", seconds)
    mon.setCursorPos((mW - #str) / 2, mH / 2)
    mon.write(str)
  end

  sleep(0.25)
end

mon.clear()
local str = "Done!"
mon.setCursorPos((mW - #str) / 2, mH / 2)
mon.write(str)