{-# LANGUAGE BangPatterns #-}

module System.IO.Streams.Concurrent.Unagi

       ( -- * Channel conversions

       , chanToInput

       , chanToOutput

       , makeChanPipe

       ) where

------------------------------------------------------------------------------

import           Control.Applicative           ((<$>), (<*>))

import           Control.Concurrent.Chan.Unagi (InChan, OutChan, newChan,

                                                readChan, writeChan)

import           Prelude                       hiding (read)

import           System.IO.Streams.Internal    (InputStream, OutputStream,

                                                makeInputStream,

                                                makeOutputStream, read)

------------------------------------------------------------------------------

-- | Writes the contents of an input stream to a channel until the input stream

-- yields end-of-stream.

inputToChan :: InputStream a -> InChan (Maybe a) -> IO ()

inputToChan is ch = go

  where

    go = do

        mb <- read is

        writeChan ch mb

        maybe (return $! ()) (const go) mb

------------------------------------------------------------------------------

-- | Turns an 'OutChan' into an input stream.

--

chanToInput :: OutChan (Maybe a) -> IO (InputStream a)

chanToInput ch = makeInputStream $! readChan ch

------------------------------------------------------------------------------

-- | Turns an 'InChan' into an output stream.

--

chanToOutput :: InChan (Maybe a) -> IO (OutputStream a)

chanToOutput = makeOutputStream . writeChan

--------------------------------------------------------------------------------

-- | Create a new pair of streams using an underlying 'Chan'. Everything written

-- to the 'OutputStream' will appear as-is on the 'InputStream'.

--

-- Since reading from the 'InputStream' and writing to the 'OutputStream' are

-- blocking calls, be sure to do so in different threads.

makeChanPipe :: IO (InputStream a, OutputStream a)

makeChanPipe = do

    (inChan, outChan) <- newChan

    (,) <$> chanToInput outChan <*> chanToOutput inChan