import Control.Monad
import Control.Monad.Trans.Class

import Control.Monad.IO.Class
import Data.Conduit

import Data.Conduit.List
import System.Environment

import System.IO

{- | Accept file paths on input, output opened file handle, and ensure that the
 - handle is always closed after its downstream pipe finishes whatever work on it. -}

fileConduit :: MonadResource m => IOMode -> Conduit FilePath m Handle

fileConduit mode = awaitForever process

  where
    process file = bracketP (openFile file mode) closeWithMsg yield

    closeWithMsg h = do

        putStrLn "Closing file"

        hClose h

{- | Print the first line from each handle on input. Don't care about the handle. -}

firstLine :: MonadIO m => Sink Handle m ()

firstLine = awaitForever (liftIO . (hGetLine >=> putStrLn))

main = do

    args <- getArgs

    runResourceT $ sourceList args =$= fileConduit ReadMode $$ firstLine