    {-# LANGUAGE NoImplicitPrelude #-}
    {-
    Copyright (C) 2006-2018 John MacFarlane <jgm@berkeley.edu>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    -}

    {- |
       Module      : Text.Pandoc.Filter
       Copyright   : Copyright (C) 2006-2018 John MacFarlane
       License     : GNU GPL, version 2 or above

       Maintainer  : John MacFarlane <jgm@berkeley@edu>
       Stability   : alpha
       Portability : portable

    Programmatically modifications of pandoc documents via JSON filters.
    -}
    module Text.Pandoc.Filter.JSON (apply) where

    import Prelude
    import Control.Monad (unless, when)
    import Control.Monad.Trans (MonadIO (liftIO))
    import Data.Aeson (eitherDecode', encode)
    import Data.Char (toLower)
    import Data.Maybe (isNothing)
    import System.Directory (executable, doesFileExist, findExecutable,
                             getPermissions)
    import System.Environment (getEnvironment)
    import System.Exit (ExitCode (..))
    import System.FilePath ((</>), takeExtension)
    import Text.Pandoc.Class (PandocIO)
    import Text.Pandoc.Error (PandocError (PandocFilterError))
    import Text.Pandoc.Definition (Pandoc)
    import Text.Pandoc.Options (ReaderOptions)
    import Text.Pandoc.Process (pipeProcess)
    import Text.Pandoc.Shared (pandocVersion)
    import qualified Control.Exception as E
    import qualified Text.Pandoc.UTF8 as UTF8

    apply :: ReaderOptions
          -> [String]
          -> FilePath
          -> Pandoc
          -> PandocIO Pandoc
    apply ropts args f = liftIO . externalFilter ropts f args

    externalFilter :: MonadIO m
                   => ReaderOptions -> FilePath -> [String] -> Pandoc -> m Pandoc
    externalFilter ropts f args' d = liftIO $ do
      exists <- doesFileExist f
      isExecutable <- if exists
                         then executable <$> getPermissions f
                         else return True
      let (f', args'') = if exists
                            then case map toLower (takeExtension f) of
                                      _      | isExecutable -> ("." </> f, args')
                                      ".py"  -> ("python", f:args')
                                      ".hs"  -> ("runhaskell", f:args')
                                      ".pl"  -> ("perl", f:args')
                                      ".rb"  -> ("ruby", f:args')
                                      ".php" -> ("php", f:args')
                                      ".js"  -> ("node", f:args')
                                      ".r"   -> ("Rscript", f:args')
                                      _      -> (f, args')
                            else (f, args')
      unless (exists && isExecutable) $ do
        mbExe <- findExecutable f'
        when (isNothing mbExe) $
          E.throwIO $ PandocFilterError f ("Could not find executable " ++ f')
      env <- getEnvironment
      let env' = Just
               ( ("PANDOC_VERSION", pandocVersion)
               : ("PANDOC_READER_OPTIONS", UTF8.toStringLazy (encode ropts))
               : env )
      (exitcode, outbs) <- E.handle filterException $
                                  pipeProcess env' f' args'' $ encode d
      case exitcode of
           ExitSuccess    -> either (E.throwIO . PandocFilterError f)
                                       return $ eitherDecode' outbs
           ExitFailure ec -> E.throwIO $ PandocFilterError f
                               ("Filter returned error status " ++ show ec)
     where filterException :: E.SomeException -> IO a
           filterException e = E.throwIO $ PandocFilterError f (show e)