{-# LANGUAGE RankNTypes #-}

module Data.Conduit.Timed (timedConduit) where

import Data.Time.Clock
import Data.Conduit
import Control.Applicative
import Control.Monad.IO.Class

-- | The timedConduit measures the elapsed time between the first
-- input being received on this pipe and the upstream close.  The
-- amount of elapsed time is added to the Pipe result time in a tuple
-- along with the upstream result time.
--
-- Example:
-- >  sourceFile "testfile.txt" >+> timedConduit >+> sinkFile "testfile.cpy" >+> (await >>= print . snd)
--
timedConduit :: MonadResource m => forall l o u . Pipe l o o u m (u, NominalDiffTime)
timedConduit = bracketP getCurrentTime (\_ -> return ()) inner
    where inner st = do r <- awaitE
                        case r of
                          Right x -> yield x >> inner st
                          Left  r -> deltaTime st >>= \t -> return (r,t)
          deltaTime st = liftIO $ flip diffUTCTime st <$> getCurrentTime