module Rhs.Schedule (Interval, pauseThread, pauseThreadUntil, at) where

import Sound.OpenSoundControl.Time (UTC, utc)
import Control.Concurrent (threadDelay)
import Control.Monad (when)

type Interval = Double
type Action = UTC -> IO (Maybe Interval)

-- | A threadDelay variant with interval given in seconds.
pauseThread :: Interval -> IO ()
pauseThread n = when (n>0) (threadDelay (floor (n * 1e6)))

-- | Pause until specified UTC time.
pauseThreadUntil :: UTC -> IO ()
pauseThreadUntil t = utc >>= pauseThread . (t -)

-- | Rescheduler
resched :: Interval -> Action -> (Maybe Interval) -> IO ()
resched _ _ Nothing = return ()
resched t f (Just i) = pauseThreadUntil t' >> f t' >>= resched t' f
    where t' = t + i

-- | Apply action at indicated time and reschedule after interval.
at :: UTC -> Action -> IO ()
at t f = pauseThreadUntil t >> f t >>= resched t f