    {-# 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.Lua
       Copyright   : Copyright (C) 2006-2018 John MacFarlane
       License     : GNU GPL, version 2 or above

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

    Apply Lua filters to modify a pandoc documents programmatically.
    -}
    module Text.Pandoc.Filter.Lua (apply) where

    import Prelude
    import Control.Exception (throw)
    import Control.Monad ((>=>))
    import Text.Pandoc.Class (PandocIO)
    import Text.Pandoc.Definition (Pandoc)
    import Text.Pandoc.Error (PandocError (PandocFilterError))
    import Text.Pandoc.Lua (Global (..), LuaException (..),
                            runLua, runFilterFile, setGlobals)
    import Text.Pandoc.Options (ReaderOptions)

    -- | Run the Lua filter in @filterPath@ for a transformation to the
    -- target format (first element in args). Pandoc uses Lua init files to
    -- setup the Lua interpreter.
    apply :: ReaderOptions
          -> [String]
          -> FilePath
          -> Pandoc
          -> PandocIO Pandoc
    apply ropts args fp doc = do
      let format = case args of
                     (x:_) -> x
                     _     -> error "Format not supplied for Lua filter"
      runLua >=> forceResult fp $ do
        setGlobals [ FORMAT format
                   , PANDOC_READER_OPTIONS ropts
                   , PANDOC_SCRIPT_FILE fp
                   ]
        runFilterFile fp doc

    forceResult :: FilePath -> Either LuaException Pandoc -> PandocIO Pandoc
    forceResult fp eitherResult = case eitherResult of
      Right x               -> return x
      Left (LuaException s) -> throw (PandocFilterError fp s)