{-# LANGUAGE ForeignFunctionInterface #-}

module Hans.Device.Tap where

import Hans.Layer.Ethernet
import Hans.Utils

import Control.Concurrent (threadWaitRead)
import Control.Monad (forever)
import Data.Word (Word8)
import Foreign.C.String (CString,withCString)
import Foreign.C.Types (CLong,CSize)
import Foreign.ForeignPtr (withForeignPtr)
import Foreign.Ptr (Ptr)
import System.Posix.Types (Fd)
import qualified Data.ByteString          as S
import qualified Data.ByteString.Internal as S



-- | Open a device by name.
openTapDevice :: DeviceName -> IO (Maybe Fd)
openTapDevice ""   = return Nothing
openTapDevice name = withCString name $ \str -> do
  ret <- c_init_tap_device str
  if ret < 0 then return Nothing else return (Just ret)


-- | Send an ethernet frame via a tap device.
tapSend :: Fd -> Packet -> IO ()
tapSend fd packet = do
  let (fptr, 0, len) = S.toForeignPtr packet
  _res <- withForeignPtr fptr $ \ptr -> c_write fd ptr (fromIntegral len)
  -- XXX: make sure to continue sending if res < len
  return ()


-- | Fork a reciever loop, and return an IO action to kill the running thread.
tapReceiveLoop :: Fd -> EthernetHandle -> IO ()
tapReceiveLoop fd eh = forever (k =<< tapReceive fd)
  where k pkt = queueEthernet eh pkt


-- | Recieve an ethernet frame from a tap device.
tapReceive :: Fd -> IO Packet
tapReceive fd = do
  threadWaitRead fd
  let packet ptr = fromIntegral `fmap` c_read fd ptr 1514
  bs <- S.createAndTrim 1514 packet
  if S.length bs <= 14
    then tapReceive fd
    else return bs


foreign import ccall unsafe "init_tap_device"
  c_init_tap_device :: CString -> IO Fd

foreign import ccall unsafe "write"
  c_write :: Fd -> Ptr Word8 -> CSize -> IO CLong

foreign import ccall unsafe "read"
  c_read :: Fd -> Ptr Word8 -> CSize -> IO CLong