Timer

-- ######################
-- ##
-- ######################

local bCable = "back" -- Side of your bundled Cable
local monitor = peripheral.wrap( "right" )
local timers = { -- Format: {"Starting Mins","Starting Secs",Function to run when done}
  {"0","20",function() rs.setBundledOutput(bCable,colors.combine(rs.getBundledInput(bCable),colors.red)) end},
  {"0","10",function() rs.setBundledOutput(bCable,colors.combine(rs.getBundledInput(bCable),colors.orange)) end}
}

--# Returns tTime in a xx:xx format
local function formatTime(tTime)
  return tTime[1]..":"..tTime[2]
end

--# Decrements each timer
local function updateTime()
  local allDone = true
  for i = 1, #timers do
    if timers[i][2] == "00" then
      if tonumber(timers[i][1]) > 0 then
        timers[i][2] = "59"
        timers[i][1] = tostring(tonumber(timers[i][1]) - 1)
        allDone = false
      elseif type(timers[i][3]) == "function" and not timers[i][4] then
        timers[i][4] = true
        timers[i][3]()
      end
    else
      timers[i][2] = tostring(tonumber(timers[i][2]) - 1)
      if tonumber(timers[i][2]) < 10 then
        timers[i][2] = "0"..(tonumber(timers[i][2]))
      end
      allDone = false
    end
  end
  return not allDone --# Returns 'true' if at least one timer counted down, false if all timers have finished
end

--# Prints time to monitor
local function printTime()
  monitor.setCursorPos(1,6)
  monitor.clearLine()
  monitor.write("         T MINUS "..formatTime(timers[1]).." MINUTES")
  monitor.setCursorPos(1,10)
  monitor.clearLine()
  monitor.write("         T MINUS "..formatTime(timers[2]).." MINUTES")
end

-- ######################
-- ##
-- ######################

monitor.setCursorPos(1, 1)
monitor.setBackgroundColor(colors.black)
monitor.clear()

monitor.setTextColor(colors.red)
monitor.setBackgroundColor(colors.black)
monitor.setTextScale(1.5)
monitor.setCursorPos(1, 3)
monitor.write("                 DANGER")
monitor.setTextColor(colors.red)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(1, 4)
monitor.write("      EMERGENCY DESTRUCTION SYSTEM")
monitor.setTextColor(colors.yellow)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(1, 5)
monitor.write("    ON ACTIVATION IT WILL DETONATE IN")
monitor.setTextColor(colors.yellow)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(1, 6)
monitor.write("         T MINUS       MINUTES")
monitor.setTextColor(colors.red)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(18, 6)
monitor.write("10:00")

monitor.setTextColor(colors.red)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(1, 8)
monitor.write("               FAILSAFE WARNING")
monitor.setTextColor(colors.yellow)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(1, 9)
monitor.write("  CUT-OFF SYSTEM WILL NOT OPERATE AFTER")
monitor.setTextColor(colors.yellow)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(1, 10)
monitor.write("          T MINUS      MINUTES")
monitor.setTextColor(colors.red)
monitor.setBackgroundColor(colors.black)
monitor.setCursorPos(19, 10)
monitor.write("5:00")

while true do

  os.pullEvent("redstone")
  if rs.getInput("left") then

    local timerID = os.startTimer(1)
    while true do
      local event = { os.pullEvent() }
      if event[1] == "timer" and event[2] == timerID then
        if not updateTime() then break end --# Stops when all functions have reached 0:00
        printTime()
        timerID = os.startTimer(1)
      end
    end

  end

end