advanced timer

local tArgs = { ... }

--usage string
usageString = "Clock & Timer\nParameters:\n\'clock\' to display current time,\n\'timer <ticks>\' to set timer\n"
--magical constants
--clock update in seconds
clockUpdate = 1
--low timer value in ticks
timerLow = 40

--current server time on script startup
startupTime = os.time()
--resume table
resumeT = {}
--operation mode
resumeT["mode"] = ""
--precision in ticks (hardcoded)
resumeT["precision"] = 20
--timer goal setting in ticks
resumeT["timerGoal"] = 0
--last saved timer value in ticks
resumeT["timerVal"] = 0
--alarm side (hardcoded)
resumeT["alarmSide"] = "top"

function ReadResume()
    if not fs.exists("resume.f") then
        print("Trying to resume without resume file, aborting...")
        return
    end
    local file = fs.open("resume.f","r")
    local sT = file.readAll()
    resumeT = textutils.unserialize(sT)
    file.close()
    return
end

function WriteResume()
    local file = fs.open("resume.f","w")
    local sT = textutils.serialize(resumeT)
    file.write(sT)
    file.close()
    return
end

--kiloticks in 24hr format as args
function KiloTicksPassed(from, to)
    if (from > to) then
    --midnight
    to = to+24.0
    end
    return (to-from)
end

function TimerFinish()
    --message
    term.setCursorPos(1,5)
    print("ALARM")
    --alarm
    rs.setOutput(resumeT["alarmSide"], true)
    --delete resume.f
    fs.delete("resume.f")
    print("\nPress any key...")
    os.pullEvent("key")
    rs.setOutput(resumeT["alarmSide"], false)
    return
end






if fs.exists("resume.f") then
    --resuming
    ReadResume()
elseif #tArgs < 1 then
    --running by hand without args
    print( usageString )
end

if (tArgs[1] == "clock") then
    resumeT["mode"] = "clock"
end

if (tArgs[1] == "timer") then
    if #tArgs < 2 then
        print(usageString)
        return
    else
        resumeT["mode"] = "timer"
        resumeT["timerGoal"] = tArgs[2]
    end
end

WriteResume()

if (resumeT["mode"] == "clock") then
    while (true) do
        term.clear()
        term.setCursorPos(1,1)
        currentTime = textutils.formatTime(os.time(), true)
        print(currentTime)
        sleep(clockUpdate)
    end
end

if (resumeT["mode"] == "timer") then
    local ticksToGo = resumeT["timerGoal"] - resumeT["timerVal"]
    --check if time interval has already passed
    if (ticksToGo < timerLow) and (KiloTicksPassed(startupTime,os.time())*1000>ticksToGo) then
        TimerFinish()
        return
    end

    local curTime = 0.0

    while (true) do
        curTime = os.time()
        WriteResume()
        ticksToGo = resumeT["timerGoal"] - resumeT["timerVal"]
        if ticksToGo < resumeT["precision"] then
            TimerFinish()
            return
        else

        term.clear()
        term.setCursorPos(1,1)
        print("Passed:")
        print(resumeT["timerVal"].." ticks or "..(resumeT["timerVal"]/60).." seconds")

        print("Remaining:")
        print(ticksToGo.." ticks or "..(ticksToGo/60).." seconds")

--      os.startTimer(resumeT["precision"])
--      os.pullEvent(timer)
        sleep(resumeT["precision"]/20)
        resumeT["timerVal"] = resumeT["timerVal"] + KiloTicksPassed(curTime,os.time())*1000
        end
    end
end