    #if __GLASGOW_HASKELL__ >= 703
    {-# LANGUAGE Trustworthy #-}
    #endif
    -- |
    -- Maintainer  : judah.jacobson@gmail.com
    -- Stability   : experimental
    -- Portability : portable (FFI)
    --
    -- This module provides a low-level interface to the C functions of the
    -- terminfo library.
    --
    -- NOTE: Since this library is built on top of the curses interface, it is not thread-safe.

    module System.Console.Terminfo.Base(
                                -- *  Initialization
                                Terminal(),
                                setupTerm,
                                setupTermFromEnv,
                                SetupTermError,
                                -- * Capabilities
                                Capability,
                                getCapability,
                                tiGetFlag,
                                tiGuardFlag,
                                tiGetNum,
                                tiGetStr,
                                -- * Output
                                -- $outputdoc
                                tiGetOutput1,
                                OutputCap,
                                TermStr,
                                -- ** TermOutput
                                TermOutput(),
                                runTermOutput,
                                hRunTermOutput,
                                termText,
                                tiGetOutput,
                                LinesAffected,
                                -- ** Monoid functions
                                Monoid(..),
                                (<#>),
                                ) where

    import Control.Monad
    import Data.Monoid
    import Foreign.C
    import Foreign.ForeignPtr
    import Foreign.Ptr
    import Foreign.Marshal
    import Foreign.Storable (peek,poke)
    import System.Environment (getEnv)
    import System.IO.Unsafe (unsafePerformIO)
    import System.IO
    import Control.Exception
    import Data.Typeable

    data TERMINAL
    newtype Terminal = Terminal (ForeignPtr TERMINAL)

    foreign import ccall "&" cur_term :: Ptr (Ptr TERMINAL)
    foreign import ccall set_curterm :: Ptr TERMINAL -> IO (Ptr TERMINAL)
    foreign import ccall "&" del_curterm :: FunPtr (Ptr TERMINAL -> IO ())

    foreign import ccall setupterm :: CString -> CInt -> Ptr CInt -> IO ()

    -- | Initialize the terminfo library to the given terminal entry.
    --
    -- Throws a 'SetupTermError' if the terminfo database could not be read.
    setupTerm :: String -> IO Terminal
    setupTerm term = bracket (peek cur_term) (poke cur_term) $ \_ ->
        withCString term $ \c_term ->
        with 0 $ \ret_ptr -> do
            -- NOTE: I believe that for the way we use terminfo
            -- (i.e. custom output function)
            -- this parameter does not affect anything.
            let stdOutput = 1
            {-- Force ncurses to return a new struct rather than
            a copy of the current one (which it would do if the
            terminal names are the same).  This prevents problems
            when calling del_term on a struct shared by more than one
            Terminal. --}
            poke cur_term nullPtr
            -- Call setupterm and check the return value.
            setupterm c_term stdOutput ret_ptr
            ret <- peek ret_ptr
            if (ret /=1)
                then throwIO $ SetupTermError
                    $ "Couldn't look up terminfo entry " ++ show term
                else do
                    cterm <- peek cur_term
                    fmap Terminal $ newForeignPtr del_curterm cterm

    data SetupTermError = SetupTermError String
                            deriving Typeable

    instance Show SetupTermError where
        show (SetupTermError str) = "setupTerm: " ++ str

    instance Exception SetupTermError where

    -- | Initialize the terminfo library, using the @TERM@ environmental variable.
    -- If @TERM@ is not set, we use the generic, minimal entry @dumb@.
    --
    -- Throws a 'SetupTermError' if the terminfo database could not be read.
    setupTermFromEnv :: IO Terminal
    setupTermFromEnv = do
        env_term <- handle handleBadEnv $ getEnv "TERM"
        let term = if null env_term then "dumb" else env_term
        setupTerm term
      where
        handleBadEnv :: IOException -> IO String
        handleBadEnv _ = return ""

    -- TODO: this isn't really thread-safe...
    withCurTerm :: Terminal -> IO a -> IO a
    withCurTerm (Terminal term) f = withForeignPtr term $ \cterm -> do
            old_term <- peek cur_term
            if old_term /= cterm
                then do
                        _ <- set_curterm cterm
                        x <- f
                        _ <- set_curterm old_term
                        return x
                else f

    ----------------------

    -- Note I'm relying on this working even for strings with unset parameters.
    strHasPadding :: String -> Bool
    strHasPadding [] = False
    strHasPadding ('$':'<':_) = True
    strHasPadding (_:cs) = strHasPadding cs

    -- | An action which sends output to the terminal.  That output may mix plain text with control
    -- characters and escape sequences, along with delays (called \"padding\") required by some older
    -- terminals.

    -- We structure this similarly to ShowS, so that appends don't cause space leaks.
    newtype TermOutput = TermOutput ([TermOutputType] -> [TermOutputType])

    data TermOutputType = TOCmd LinesAffected String
                        | TOStr String

    instance Monoid TermOutput where
        mempty = TermOutput id
        TermOutput xs `mappend` TermOutput ys = TermOutput (xs . ys)

    termText :: String -> TermOutput
    termText str = TermOutput (TOStr str :)

    -- | Write the terminal output to the standard output device.
    runTermOutput :: Terminal -> TermOutput -> IO ()
    runTermOutput = hRunTermOutput stdout

    -- | Write the terminal output to the terminal or file managed by the given
    -- 'Handle'.
    hRunTermOutput :: Handle -> Terminal -> TermOutput -> IO ()
    hRunTermOutput h term (TermOutput to) = do
        putc_ptr <- mkCallback putc
        withCurTerm term $ mapM_ (writeToTerm putc_ptr h) (to [])
        freeHaskellFunPtr putc_ptr
        hFlush h
      where
        putc c = let c' = toEnum $ fromEnum c
                 in hPutChar h c' >> hFlush h >> return c

    -- NOTE: Currently, the output is checked every time tparm is called.
    -- It might be faster to check for padding once in tiGetOutput1.
    writeToTerm :: FunPtr CharOutput -> Handle -> TermOutputType -> IO ()
    writeToTerm putc h (TOCmd numLines s)
        | strHasPadding s = tPuts s numLines putc
        | otherwise = hPutStr h s
    writeToTerm _ h (TOStr s) = hPutStr h s

    infixl 2 <#>

    -- | An operator version of 'mappend'.
    (<#>) :: Monoid m => m -> m -> m
    (<#>) = mappend
    ---------------------------------

    -- | A feature or operation which a 'Terminal' may define.
    newtype Capability a = Capability (Terminal -> IO (Maybe a))

    getCapability :: Terminal -> Capability a -> Maybe a
    getCapability term (Capability f) = unsafePerformIO $ withCurTerm term (f term)

    -- Note that the instances for Capability of Functor, Monad and MonadPlus
    -- use the corresponding instances for Maybe.
    instance Functor Capability where
        fmap f (Capability g) = Capability $ \t -> fmap (fmap f) (g t)

    instance Monad Capability where
        return = Capability . const . return . Just
        Capability f >>= g = Capability $ \t -> do
            mx <- f t
            case mx of
                Nothing -> return Nothing
                Just x -> let Capability g' = g x in g' t

    instance MonadPlus Capability where
        mzero = Capability (const $ return Nothing)
        Capability f `mplus` Capability g = Capability $ \t -> do
            mx <- f t
            case mx of
                Nothing -> g t
                _ -> return mx

    foreign import ccall tigetnum :: CString -> IO CInt

    -- | Look up a numeric capability in the terminfo database.
    tiGetNum :: String -> Capability Int
    tiGetNum cap = Capability $ const $ do
                    n <- fmap fromEnum (withCString cap tigetnum)
                    if n >= 0
                        then return (Just n)
                        else return Nothing

    foreign import ccall tigetflag :: CString -> IO CInt
    -- | Look up a boolean capability in the terminfo database.
    --
    -- Unlike 'tiGuardFlag', this capability never fails; it returns 'False' if the
    -- capability is absent or set to false, and returns 'True' otherwise.
    --
    tiGetFlag :: String -> Capability Bool
    tiGetFlag cap = Capability $ const $ fmap (Just . (>0)) $
                            withCString cap tigetflag

    -- | Look up a boolean capability in the terminfo database, and fail if
    -- it\'s not defined.
    tiGuardFlag :: String -> Capability ()
    tiGuardFlag cap = tiGetFlag cap >>= guard

    foreign import ccall tigetstr :: CString -> IO CString

    {-# DEPRECATED tiGetStr "use tiGetOutput instead." #-}
    -- | Look up a string capability in the terminfo database.  NOTE: This function is deprecated; use
    -- 'tiGetOutput1' instead.
    tiGetStr :: String -> Capability String
    tiGetStr cap = Capability $ const $ do
                    result <- withCString cap tigetstr
                    if result == nullPtr || result == neg1Ptr
                        then return Nothing
                        else fmap Just (peekCString result)
        where
            -- hack; tigetstr sometimes returns (-1)
            neg1Ptr = nullPtr `plusPtr` (-1)

    ---------------

    foreign import ccall tparm ::
        CString -> CLong -> CLong -> CLong -> CLong -> CLong -> CLong
        -> CLong -> CLong -> CLong -- p1,...,p9
        -> IO CString

    -- Note: I may want to cut out the middleman and pipe tGoto/tGetStr together
    -- with tput without a String marshall in the middle.
    -- directly without

    tParm :: String -> Capability ([Int] -> String)
    tParm cap = Capability $ \t -> return $ Just
            $ \ps -> unsafePerformIO $ withCurTerm t $
                        tparm' (map toEnum ps ++ repeat 0)
        where tparm' (p1:p2:p3:p4:p5:p6:p7:p8:p9:_)
                = withCString cap $ \c_cap -> do
                    result <- tparm c_cap p1 p2 p3 p4 p5 p6 p7 p8 p9
                    if result == nullPtr
                        then return ""
                        else peekCString result
              tparm' _ = fail "tParm: List too short"

    -- | Look up an output capability in the terminfo database.
    tiGetOutput :: String -> Capability ([Int] -> LinesAffected -> TermOutput)
    tiGetOutput cap = do
        str <- tiGetStr cap
        f <- tParm str
        return $ \ps la -> fromStr la $ f ps

    fromStr :: LinesAffected -> String -> TermOutput
    fromStr la s = TermOutput (TOCmd la s :)

    type CharOutput = CInt -> IO CInt

    foreign import ccall "wrapper" mkCallback :: CharOutput -> IO (FunPtr CharOutput)

    foreign import ccall tputs :: CString -> CInt -> FunPtr CharOutput -> IO ()

    -- | A parameter to specify the number of lines affected.  Some capabilities
    -- (e.g., @clear@ and @dch1@) use
    -- this parameter on some terminals to compute variable-length padding.
    type LinesAffected = Int

    -- | Output a string capability.  Applys padding information to the string if
    -- necessary.
    tPuts :: String -> LinesAffected -> FunPtr CharOutput -> IO ()
    tPuts s n putc = withCString s $ \c_str -> tputs c_str (toEnum n) putc

    -- | Look up an output capability which takes a fixed number of parameters
    -- (for example, @Int -> Int -> TermOutput@).
    --
    -- For capabilities which may contain variable-length
    -- padding, use 'tiGetOutput' instead.
    tiGetOutput1 :: forall f . OutputCap f => String -> Capability f
    tiGetOutput1 str = do
        cap <- tiGetStr str
        guard (hasOkPadding (undefined :: f) cap)
        f <- tParm cap
        return $ outputCap f []

    -- OK, this is the structure that I want:
    class OutputCap f where
        hasOkPadding :: f -> String -> Bool
        outputCap :: ([Int] -> String) -> [Int] -> f

    instance OutputCap [Char] where
        hasOkPadding _ = not . strHasPadding
        outputCap f xs = f (reverse xs)

    instance OutputCap TermOutput where
        hasOkPadding _ = const True
        outputCap f xs = fromStr 1 $ f $ reverse xs

    instance (Enum p, OutputCap f) => OutputCap (p -> f) where
        outputCap f xs = \x -> outputCap f (fromEnum x:xs)
        hasOkPadding _ = hasOkPadding (undefined :: f)

    {- $outputdoc
    Terminfo contains many string capabilities for special effects.
    For example, the @cuu1@ capability moves the cursor up one line; on ANSI terminals
    this is accomplished by printing the control sequence @\"\\ESC[A\"@.
    However, some older terminals also require \"padding\", or short pauses, after certain commands.
    For example, when @TERM=vt100@ the @cuu1@ capability is @\"\\ESC[A$\<2\>\"@, which instructs terminfo
    to pause for two milliseconds after outputting the control sequence.

    The 'TermOutput' monoid abstracts away all padding and control
    sequence output.  Unfortunately, that datatype is difficult to integrate into existing 'String'-based APIs
    such as pretty-printers.  Thus, as a workaround, 'tiGetOutput1' also lets us access the control sequences as 'String's.  The one caveat is that it will not allow you to access padded control sequences as Strings.  For example:

       > > t <- setupTerm "vt100"
       > > isJust (getCapability t (tiGetOutput1 "cuu1") :: Maybe String)
       > False
       > > isJust (getCapability t (tiGetOutput1 "cuu1") :: Maybe TermOutput)
       > True

    'String' capabilities will work with software-based terminal types such as @xterm@ and @linux@.
    However, you should use 'TermOutput' if compatibility with older terminals is important.
    Additionally, the @visualBell@ capability which flashes the screen usually produces its effect with a padding directive, so it will only work with 'TermOutput'.

    -}

    class (Monoid s, OutputCap s) => TermStr s

    instance TermStr [Char]
    instance TermStr TermOutput