module Linux.Systemd
  ( listenFds
  , isSocket
  ) where

import Foreign.C.Types (CInt(..))
import System.Posix.Types (Fd(..))
import Foreign.C.Error (Errno,getErrno)
import Posix.Socket.Types (Type(..),Family(..))

foreign import ccall unsafe "systemd/sd-daemon.h sd_listen_fds"
  c_listenFds :: CInt -> IO CInt

foreign import ccall unsafe "systemd/sd-daemon.h sd_is_socket"
  c_isSocket :: Fd -> Family -> Type -> CInt -> IO CInt

-- | Check for file descriptors passed by the system manager. Returns
-- the number of received file descriptors. If no file descriptors
-- have been received, zero is returned.
listenFds ::
     CInt -- ^ unset environment (non-zero unsets @LISTEN_FDS@, @LISTEN_PID@, and @LISTEN_FDNAMES@)
  -> IO (Either Errno CInt)
listenFds a = c_listenFds a >>= errorsFromInt

isSocket :: 
     Fd -- ^ File descriptor
  -> Family -- ^ Socket family
  -> Type -- ^ Socket type
  -> CInt -- ^ Positive: require listen mode. Zero: require non-listening mode.
  -> IO (Either Errno CInt)
isSocket a b c d = c_isSocket a b c d >>= errorsFromInt

errorsFromInt :: CInt -> IO (Either Errno CInt)
errorsFromInt r = if r >= 0
  then pure (Right r)
  else fmap Left getErrno