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{-
Copyright © 2017 Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>

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.Lua
   Copyright   : Copyright © 2017 Albert Krewinkel
   License     : GNU GPL, version 2 or above

   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
   Stability   : alpha

Running pandoc Lua filters.
-}
module Text.Pandoc.Lua
  ( LuaException (..)
  , runLuaFilter
  , runPandocLua
  ) where

import Control.Monad ((>=>))
import Foreign.Lua (FromLuaStack (peek), Lua, LuaException (..),
                    Status (OK), ToLuaStack (push))
import Text.Pandoc.Class (PandocIO)
import Text.Pandoc.Definition (Pandoc)
import Text.Pandoc.Lua.Filter (LuaFilter, walkMWithLuaFilter)
import Text.Pandoc.Lua.Init (runPandocLua)
import Text.Pandoc.Lua.Util (popValue)
import qualified Foreign.Lua as Lua

-- | Run the Lua filter in @filterPath@ for a transformation to target
-- format @format@. Pandoc uses Lua init files to setup the Lua
-- interpreter.
runLuaFilter :: FilePath -> String
             -> Pandoc -> PandocIO (Either LuaException Pandoc)
runLuaFilter filterPath format doc =
  runPandocLua (runLuaFilter' filterPath format doc)

runLuaFilter' :: FilePath -> String
              -> Pandoc -> Lua Pandoc
runLuaFilter' filterPath format pd = do
  -- store module in global "pandoc"
  registerFormat
  top <- Lua.gettop
  stat <- Lua.dofile filterPath
  if stat /= OK
    then do
      luaErrMsg <- peek (-1) <* Lua.pop 1
      Lua.throwLuaError luaErrMsg
    else do
      newtop <- Lua.gettop
      -- Use the returned filters, or the implicitly defined global filter if
      -- nothing was returned.
      luaFilters <- if (newtop - top >= 1)
                    then peek (-1)
                    else Lua.getglobal "_G" *> fmap (:[]) popValue
      runAll luaFilters pd
 where
  registerFormat = do
    push format
    Lua.setglobal "FORMAT"

runAll :: [LuaFilter] -> Pandoc -> Lua Pandoc
runAll = foldr ((>=>) . walkMWithLuaFilter) return