{-# LANGUAGE CPP #-}
{-# LANGUAGE ForeignFunctionInterface #-}

module Network.Wai.Handler.SCGI (
    run,
    runSendfile,
) where

import Data.ByteString (ByteString)
import qualified Data.ByteString as S
import qualified Data.ByteString.Char8 as S8
import Data.ByteString.Lazy.Internal (defaultChunkSize)
import qualified Data.ByteString.Unsafe as S
import Data.IORef (IORef, newIORef, readIORef, writeIORef)
import Data.Maybe (fromMaybe, listToMaybe)
import Foreign.C (CChar, CInt (..))
import Foreign.Marshal.Alloc (free, mallocBytes)
import Foreign.Ptr (Ptr, castPtr, nullPtr)
import Network.Wai (Application)
import Network.Wai.Handler.CGI (requestBodyFunc, runGeneric)

run :: Application -> IO ()
run app = runOne Nothing app >> run app

runSendfile :: ByteString -> Application -> IO ()
runSendfile sf app = runOne (Just sf) app >> runSendfile sf app

runOne :: Maybe ByteString -> Application -> IO ()
runOne sf app = do
    socket <- c'accept 0 nullPtr nullPtr
    headersBS <- readNetstring socket
    let headers = parseHeaders $ S.split 0 headersBS
    let conLen =
            fromMaybe 0 $ do
                (_, conLenS) <- listToMaybe headers
                (i, _) <- listToMaybe $ reads conLenS
                pure i
    conLenI <- newIORef conLen
    runGeneric
        headers
        (requestBodyFunc $ input socket conLenI)
        (write socket)
        sf
        app
    drain socket conLenI
    _ <- c'close socket
    return ()

write :: CInt -> S.ByteString -> IO ()
write socket bs = S.unsafeUseAsCStringLen bs $ \(s, l) -> do
    _ <- c'write socket s (fromIntegral l)
    return ()

input :: CInt -> IORef Int -> Int -> IO (Maybe S.ByteString)
input socket ilen rlen = do
    len <- readIORef ilen
    case len of
        0 -> return Nothing
        _ -> do
            bs <-
                readByteString socket $
                    minimum [defaultChunkSize, len, rlen]
            writeIORef ilen $ len - S.length bs
            return $ Just bs

drain :: CInt -> IORef Int -> IO () -- FIXME do it in chunks
drain socket ilen = do
    len <- readIORef ilen
    _ <- readByteString socket len
    return ()

parseHeaders :: [S.ByteString] -> [(String, String)]
parseHeaders (x : y : z) = (S8.unpack x, S8.unpack y) : parseHeaders z
parseHeaders _ = []

readNetstring :: CInt -> IO S.ByteString
readNetstring socket = do
    len <- readLen 0
    bs <- readByteString socket len
    _ <- readByteString socket 1 -- the comma
    return bs
  where
    readLen l = do
        bs <- readByteString socket 1
        case S8.unpack bs of
            [':'] -> return l
            [c] -> readLen $ l * 10 + (fromEnum c - fromEnum '0')
            _ -> error "Network.Wai.Handler.SCGI.readNetstring: should never happen"

readByteString :: CInt -> Int -> IO S.ByteString
readByteString socket len = do
    buf <- mallocBytes len
    _ <- c'read socket buf $ fromIntegral len
    S.unsafePackCStringFinalizer (castPtr buf) len $ free buf

foreign import ccall unsafe "accept"
    c'accept :: CInt -> Ptr a -> Ptr a -> IO CInt

#if WINDOWS
foreign import ccall unsafe "_close"
    c'close :: CInt -> IO CInt

foreign import ccall unsafe "_write"
    c'write :: CInt -> Ptr CChar -> CInt -> IO CInt

foreign import ccall unsafe "_read"
    c'read :: CInt -> Ptr CChar -> CInt -> IO CInt
#else
foreign import ccall unsafe "close"
    c'close :: CInt -> IO CInt

foreign import ccall unsafe "write"
    c'write :: CInt -> Ptr CChar -> CInt -> IO CInt

foreign import ccall unsafe "read"
    c'read :: CInt -> Ptr CChar -> CInt -> IO CInt
#endif