module System.Console.Haskeline.InputT where


import System.Console.Haskeline.Command.History
import System.Console.Haskeline.Command.Undo
import System.Console.Haskeline.Monads as Monads
import System.Console.Haskeline.Prefs
import System.Console.Haskeline.Command(Layout)
import System.Console.Haskeline.Completion
import System.Console.Haskeline.Backend
import System.Console.Haskeline.Term

import System.Directory(getHomeDirectory)
import System.FilePath
import Control.Applicative
import Control.Monad(liftM, ap)

-- | Application-specific customizations to the user interface.
data Settings m = Settings {complete :: CompletionFunc m, -- ^ Custom tab completion
                            historyFile :: Maybe FilePath
                            }

-- | Because 'complete' is the only field of 'Settings' depending on @m@,
-- the expression @defaultSettings {completionFunc = f}@ leads to a type error
-- from being too general.  This function works around that issue, and may become unnecessary if another field
-- depending on @m@ is added.

setComplete :: CompletionFunc m -> Settings m -> Settings m
setComplete f s = s {complete = f}


-- | A monad transformer which carries all of the state and settings
-- relevant to a line-reading application.
newtype InputT m a = InputT {unInputT :: ReaderT RunTerm
                                (StateT History (ReaderT Prefs 
                                (ReaderT (Settings m) m))) a}
                            deriving (Monad,MonadIO, MonadState History,
                                        MonadReader Prefs, MonadReader (Settings m),
                                        MonadReader RunTerm)

instance Monad m => Functor (InputT m) where
    fmap = liftM

instance Monad m => Applicative (InputT m) where
    pure = return
    (<*>) = ap

instance MonadTrans InputT where
    lift = InputT . lift . lift . lift . lift

instance MonadException m => MonadException (InputT m) where
    block = InputT . block . unInputT
    unblock = InputT . unblock . unInputT
    catch f h = InputT $ Monads.catch (unInputT f) (unInputT . h)

-- for internal use only
type InputCmdT m = ReaderT Layout (UndoT (StateT HistLog 
                (ReaderT Prefs (ReaderT (Settings m) m))))

instance MonadIO m => MonadLayout (InputCmdT m) where

runInputCmdT :: MonadIO m => TermOps -> InputCmdT m a -> InputT m a
runInputCmdT tops f = InputT $ do
    layout <- liftIO $ getLayout tops
    lift $ runHistLog $ runUndoT $ runReaderT' layout f


liftCmdT :: Monad m => m a -> InputCmdT m a
liftCmdT = lift  . lift . lift . lift . lift

runInputTWithPrefs :: MonadException m => Prefs -> Settings m -> InputT m a -> m a
runInputTWithPrefs prefs settings (InputT f) = bracket (liftIO myRunTerm)
    (liftIO . closeTerm)
    $ \run -> runReaderT' settings $ runReaderT' prefs 
        $ runHistoryFromFile (historyFile settings) (maxHistorySize prefs) 
        $ runReaderT f run
        
-- | Run a line-reading application, reading user 'Prefs' from 
-- @~/.haskeline@
runInputT :: MonadException m => Settings m -> InputT m a -> m a
runInputT settings f = do
    prefs <- liftIO readPrefsFromHome
    runInputTWithPrefs prefs settings f

-- | Read 'Prefs' from @~/.haskeline.@   If there is an error reading the file,
-- the 'defaultPrefs' will be returned.
readPrefsFromHome :: IO Prefs
readPrefsFromHome = handle (\(_::IOException) -> return defaultPrefs) $ do
    home <- getHomeDirectory
    readPrefs (home </> ".haskeline")