{-# LANGUAGE Safe, CApiFFI #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  System.Posix.Directory.Common
-- Copyright   :  (c) The University of Glasgow 2002
-- License     :  BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer  :  libraries@haskell.org
-- Stability   :  provisional
-- Portability :  non-portable (requires POSIX)
--
-- POSIX directory support
--
-----------------------------------------------------------------------------

#include "HsUnix.h"

module System.Posix.Directory.Common (
       DirStream(..), CDir, CDirent, DirStreamOffset(..),
       unsafeOpenDirStreamFd,
       rewindDirStream,
       closeDirStream,
#ifdef HAVE_SEEKDIR
       seekDirStream,
#endif
#ifdef HAVE_TELLDIR
       tellDirStream,
#endif
       changeWorkingDirectoryFd,
  ) where

import Control.Exception (mask_)
import Control.Monad (void, when)
import System.Posix.Types
import Foreign hiding (void)
import Foreign.C

#if !defined(HAVE_FCHDIR)
import System.IO.Error ( ioeSetLocation )
import GHC.IO.Exception ( unsupportedOperation )
#endif

newtype DirStream = DirStream (Ptr CDir)

data {-# CTYPE "DIR" #-} CDir
data {-# CTYPE "struct dirent" #-} CDirent

-- | Call @fdopendir@ to obtain a directory stream for @fd@. @fd@ must not be
-- otherwise used after this.
--
-- On success, it is owned by the returned 'DirStream', which should be closed
-- via 'closeDirStream' when no longer needed.  On error, the file descriptor
-- is automatically closed and then an exception is thrown.  There is no code
-- path in which the file descriptor remains open and yet not owned by a
-- returned 'DirStream'.
--
-- The input file descriptor must not have been used with @threadWaitRead@ or
-- @threadWaitWrite@.
unsafeOpenDirStreamFd :: Fd -> IO DirStream
unsafeOpenDirStreamFd (Fd fd) = mask_ $ do
    ptr <- c_fdopendir fd
    when (ptr == nullPtr) $ do
        errno <- getErrno
        void $ c_close fd
        ioError (errnoToIOError "openDirStreamFd" errno Nothing Nothing)
    return $ DirStream ptr

-- We need c_close here, because 'closeFd' throws exceptions on error,
-- but we want to silently close the (presumably directory) descriptor.
foreign import ccall unsafe "HsUnix.h close"
   c_close :: CInt -> IO CInt

-- NOTE: It is /critical/ to use "capi" and "dirent.h" here, because system
-- headers on e.g. macOS alias this function, and linking directly to the
-- "fdopendir" symbol in libc leads to a crash!
--
foreign import capi unsafe "dirent.h fdopendir"
    c_fdopendir :: CInt -> IO (Ptr CDir)

-- | @rewindDirStream dp@ calls @rewinddir@ to reposition
--   the directory stream @dp@ at the beginning of the directory.
rewindDirStream :: DirStream -> IO ()
rewindDirStream (DirStream dirp) = c_rewinddir dirp

foreign import ccall unsafe "rewinddir"
   c_rewinddir :: Ptr CDir -> IO ()

-- | @closeDirStream dp@ calls @closedir@ to close
--   the directory stream @dp@.
closeDirStream :: DirStream -> IO ()
closeDirStream (DirStream dirp) = do
  throwErrnoIfMinus1Retry_ "closeDirStream" (c_closedir dirp)

foreign import ccall unsafe "closedir"
   c_closedir :: Ptr CDir -> IO CInt

newtype DirStreamOffset = DirStreamOffset COff

#ifdef HAVE_SEEKDIR
seekDirStream :: DirStream -> DirStreamOffset -> IO ()
seekDirStream (DirStream dirp) (DirStreamOffset off) =
  c_seekdir dirp (fromIntegral off) -- TODO: check for CLong/COff overflow

foreign import ccall unsafe "seekdir"
  c_seekdir :: Ptr CDir -> CLong -> IO ()
#endif

#ifdef HAVE_TELLDIR
tellDirStream :: DirStream -> IO DirStreamOffset
tellDirStream (DirStream dirp) = do
  off <- c_telldir dirp
  return (DirStreamOffset (fromIntegral off)) -- TODO: check for overflow

foreign import ccall unsafe "telldir"
  c_telldir :: Ptr CDir -> IO CLong
#endif

#if defined(HAVE_FCHDIR)

changeWorkingDirectoryFd :: Fd -> IO ()
changeWorkingDirectoryFd (Fd fd) =
  throwErrnoIfMinus1Retry_ "changeWorkingDirectoryFd" (c_fchdir fd)

foreign import ccall unsafe "fchdir"
  c_fchdir :: CInt -> IO CInt

#else

{-# WARNING changeWorkingDirectoryFd "operation will throw 'IOError' \"unsupported operation\" (CPP guard: @#if HAVE_FCHDIR@)" #-}
changeWorkingDirectoryFd :: Fd -> IO ()
changeWorkingDirectoryFd _ = ioError (ioeSetLocation unsupportedOperation "changeWorkingDirectoryFd")

#endif // HAVE_FCHDIR