{-# LANGUAGE CPP #-}
module Timers where

#if MIN_VERSION_time(1,8,0)
import Data.Time.Clock.System
#else
import System.Time
#endif
import Data.IORef
import PQueue
import Stypes(Timer(..))

type TimersVar = IORef Timers
data Timers = Timers { tq::PQueue MsTime (MsTime,Timer),tno::Int }

type MsTime = Int

initTimers = newIORef (Timers empty 0)

createTimer tref interval first =
  do Timers tq tno <- readIORef tref
     now <- mstime
     writeIORef tref (Timers (insert tq (now+first,(interval,Ti tno))) (tno+1))
     return (Ti tno)

destroyTimer tref t =
  do Timers tq tno <- readIORef tref
     writeIORef tref (Timers (remove tq t) tno)

timeLeft tref =
  do tqv <- tq `fmap` readIORef tref
     case inspect tqv of
       Nothing -> return Nothing
       Just ((t,_),_) ->
         do ms <- mstime
            return . Just . max 0 $ t - ms

removeTimeQ tref =
  do Timers tqv tno <- readIORef tref
     case inspect tqv of
       Just ((first,v@(interval,tnov)),tqv') -> do
          let tqv2 = if interval == 0 then tqv'
                     else insert tqv' (first+interval,v)
          writeIORef tref (Timers tqv2 tno)
          return tnov


mstime :: IO MsTime
mstime =
#if MIN_VERSION_time(1,8,0)
  do MkSystemTime s ns <- getSystemTime
#else
  do TOD s ps <- getClockTime
     let ns = ps `quot` 1000
#endif
     return (fromIntegral s * 1000 + fromIntegral ns `quot` 1000000)
     -- This overflows with 32-bit Int, but it's ok.