{-# LANGUAGE  CPP
            , PackageImports
            , ScopedTypeVariables
            , FlexibleContexts #-}

-- |Random and Binary IO with generic Iteratees, using File Descriptors for IO.
-- when available, these are the preferred functions for performing IO as they
-- run in constant space and function properly with sockets, pipes, etc.

module Data.Iteratee.IO.Fd(
#if defined(USE_POSIX)
  -- * File enumerators
  -- ** FileDescriptor based enumerators for monadic iteratees
  enumFd
  ,enumFdCatch
  ,enumFdRandom
  ,enumFile
  ,enumFileRandom
  -- * Iteratee drivers
  ,fileDriverFd
  ,fileDriverRandomFd
#endif
)

where

#if defined(USE_POSIX)
import Data.Iteratee.Base.ReadableChunk
import Data.Iteratee.Iteratee
import Data.Iteratee.Binary()
import Data.Iteratee.IO.Base

import Control.Concurrent (yield)
import Control.Monad
import Control.Monad.Trans.Control
import Control.Exception.Lifted
import Control.Monad.IO.Class

import Foreign.C.Error
import Foreign.Ptr
import Foreign.Storable
import Foreign.Marshal.Alloc

import System.IO (SeekMode(..))

import "unix-bytestring" System.Posix.IO.ByteString

-- ------------------------------------------------------------------------
-- Binary Random IO enumerators

makefdCallback ::
  (MonadIO m, NullPoint s, ReadableChunk s el) =>
  Ptr el
  -> ByteCount
  -> Fd
  -> Callback st m s
makefdCallback p bufsize fd st = do
  n <- liftIO $ tryFdReadBuf fd (castPtr p) bufsize
  case n of
    Left  (Errno err) -> return $ Left (error $ "read failed: " ++ show err)
    Right 0   -> liftIO yield >> return (Right ((Finished, st), empty))
    Right n'  -> liftM (\s -> Right ((HasMore, st), s)) $
                   readFromPtr p (fromIntegral n')
{-# INLINABLE makefdCallback #-}

-- |The enumerator of a POSIX File Descriptor.  This version enumerates
-- over the entire contents of a file, in order, unless stopped by
-- the iteratee.  In particular, seeking is not supported.
enumFd
  :: forall s el m a.(NullPoint s, ReadableChunk s el, MonadIO m, MonadBaseControl IO m) =>
     Int
     -> Fd
     -> Enumerator s m a
enumFd bs fd iter =
  let bufsize = bs * (sizeOf (undefined :: el))
  in bracket (liftIO $ mallocBytes bufsize)
             (liftIO . free)
             (\p -> enumFromCallback (makefdCallback p (fromIntegral bufsize) fd) () iter)
{-# INLINABLE enumFd #-}

-- |A variant of enumFd that catches exceptions raised by the @Iteratee@.
enumFdCatch
 :: forall e s el m a.(IException e, NullPoint s, ReadableChunk s el, MonadIO m, MonadBaseControl IO m)
    => Int
    -> Fd
    -> (e -> m (Maybe EnumException))
    -> Enumerator s m a
enumFdCatch bs fd handler iter =
  let bufsize = bs * (sizeOf (undefined :: el))
  in bracket (liftIO $ mallocBytes bufsize)
             (liftIO . free)
             (\p -> enumFromCallbackCatch (makefdCallback p (fromIntegral bufsize) fd) handler () iter)
{-# INLINABLE enumFdCatch #-}


-- |The enumerator of a POSIX File Descriptor: a variation of @enumFd@ that
-- supports RandomIO (seek requests).
enumFdRandom
 :: forall s el m a.(NullPoint s, ReadableChunk s el, MonadIO m, MonadBaseControl IO m) =>
    Int
    -> Fd
    -> Enumerator s m a
enumFdRandom bs fd iter = enumFdCatch bs fd handler iter
  where
    handler (SeekException off) =
      liftM (either
             (const . Just $ enStrExc "Error seeking within file descriptor")
             (const Nothing))
            . liftIO . tryFdSeek fd AbsoluteSeek $ fromIntegral off
{-# INLINABLE enumFdRandom #-}

fileDriver
  :: (MonadIO m, MonadBaseControl IO m, ReadableChunk s el) =>
     (Int -> Fd -> Enumerator s m a)
     -> Int
     -> Iteratee s m a
     -> FilePath
     -> m a
fileDriver enumf bufsize iter filepath = bracket
  (liftIO $ openFd filepath ReadOnly Nothing defaultFileFlags)
  (liftIO . closeFd)
  (run <=< flip (enumf bufsize) iter)
{-# INLINABLE fileDriver #-}

-- |Process a file using the given @Iteratee@.
fileDriverFd
  :: (NullPoint s, MonadIO m, MonadBaseControl IO m, ReadableChunk s el) =>
     Int -- ^Buffer size (number of elements)
     -> Iteratee s m a
     -> FilePath
     -> m a
fileDriverFd = fileDriver enumFd
{-# INLINABLE fileDriverFd #-}

-- |A version of fileDriverFd that supports seeking.
fileDriverRandomFd
  :: (NullPoint s, MonadIO m, MonadBaseControl IO m, ReadableChunk s el) =>
     Int
     -> Iteratee s m a
     -> FilePath
     -> m a
fileDriverRandomFd = fileDriver enumFdRandom
{-# INLINABLE fileDriverRandomFd #-}

enumFile' :: (NullPoint s, MonadIO m, MonadBaseControl IO m, ReadableChunk s el) =>
  (Int -> Fd -> Enumerator s m a)
  -> Int -- ^Buffer size
  -> FilePath
  -> Enumerator s m a
enumFile' enumf bufsize filepath iter = bracket
  (liftIO $ openFd filepath ReadOnly Nothing defaultFileFlags)
  (liftIO . closeFd)
  (flip (enumf bufsize) iter)
{-# INLINABLE enumFile' #-}

enumFile ::
  (NullPoint s, MonadIO m, MonadBaseControl IO m, ReadableChunk s el)
  => Int                 -- ^Buffer size
  -> FilePath
  -> Enumerator s m a
enumFile = enumFile' enumFd
{-# INLINABLE enumFile #-}

enumFileRandom ::
  (NullPoint s, MonadIO m, MonadBaseControl IO m, ReadableChunk s el)
  => Int                 -- ^Buffer size
  -> FilePath
  -> Enumerator s m a
enumFileRandom = enumFile' enumFdRandom
{-# INLINABLE enumFileRandom #-}


#endif