{-# LANGUAGE MultiParamTypeClasses #-}
{-
  This module is part of Chatty.
  Copyleft (c) 2014 Marvin Cohrs

  All wrongs reversed. Sharing is an act of love, not crime.
  Please share Antisplice with everyone you like.

  Chatty is free software: you can redistribute it and/or modify
  it under the terms of the GNU Affero General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Chatty is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  GNU Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License
  along with Chatty. If not, see <http://www.gnu.org/licenses/>.
-}

module System.Chatty.Filesystem where

import Control.Monad
import Control.Monad.State
import Control.Monad.Identity
import Data.Chatty.Atoms
import Text.Chatty.Printer
import Text.Chatty.Scanner

data FSExec a = FSSucc a
              | NoPermission
              | NotFound

data File m = File {
    loadFun :: m (FSExec ()),
    saveFun :: m (FSExec ()),
    closeFun :: m (),
    leftBehind :: String,
    rightPending :: String
  }
type FileA m = Atom (File m)

class ChAtoms m => ChFilesystem m where
  fopen :: String -> m (FSExec (FileA m))

class Monad m => CanLoad m n where
  fload :: FileA n -> m (FSExec ())

class Monad m => CanSave m n where
  fsave :: FileA n -> m (FSExec ())

data FilePrinterT m a = FilePrinter { runFilePrinterT :: FileA m -> m a }
data FileScannerT m a = FileScanner { runFileScannerT :: FileA m -> m a }

instance Monad m => Monad (FilePrinterT m) where
  return a = FilePrinter $ \_ -> return a
  m >>= f = FilePrinter $ \d -> do a <- runFilePrinterT m d; runFilePrinterT (f a) d

instance Monad m => Monad (FileScannerT m) where
  return a = FileScanner $ \_ -> return a
  m >>= f = FileScanner $ \d -> do a <- runFileScannerT m d; runFileScannerT (f a) d

instance Functor f => Functor (FilePrinterT f) where
  fmap f a = FilePrinter $ fmap f . runFilePrinterT a

instance Functor f => Functor (FileScannerT f) where
  fmap f a = FileScanner $ fmap f . runFileScannerT a

instance MonadTrans FilePrinterT where
  lift m = FilePrinter $ \_ -> m

instance MonadTrans FileScannerT where
  lift m = FileScanner $ \_ -> m

instance MonadIO m => MonadIO (FilePrinterT m) where
  liftIO = lift . liftIO

instance MonadIO m => MonadIO (FileScannerT m) where
  liftIO = lift . liftIO

instance ChAtoms m => ChPrinter (FilePrinterT m) where
  mprint s = FilePrinter $ \d -> do
    f <- getAtom d
    putAtom d f{leftBehind=reverse (take (length s) $ rightPending f) ++ leftBehind f, rightPending=drop (length s) $ rightPending f}

instance ChAtoms m => ChScanner (FileScannerT m) where
  mscan1 = FileScanner $ \d -> do
    f <- getAtom d
    putAtom d f{leftBehind=head (rightPending f) : leftBehind f, rightPending=tail $ rightPending f}
    return $ head $ rightPending f
  mscanL = FileScanner $ liftM rightPending . getAtom
  mscannable = FileScanner $ liftM (not . null . rightPending) . getAtom
  mready = mscannable