    {-
    Copyright © 2017-2018 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
    -}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE NoImplicitPrelude #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    {- |
       Module      : Text.Pandoc.Lua.Packages
       Copyright   : Copyright © 2017-2018 Albert Krewinkel
       License     : GNU GPL, version 2 or above

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

    Pandoc module for lua.
    -}
    module Text.Pandoc.Lua.Packages
      ( LuaPackageParams (..)
      , installPandocPackageSearcher
      ) where

    import Prelude
    import Control.Monad (forM_)
    import Data.ByteString (ByteString)
    import Data.IORef (IORef)
    import Foreign.Lua (Lua, NumResults, liftIO)
    import Text.Pandoc.Class (CommonState, readDataFile, runIO, setUserDataDir)
    import Text.Pandoc.MediaBag (MediaBag)

    import qualified Foreign.Lua as Lua
    import Text.Pandoc.Lua.Module.Pandoc as Pandoc
    import Text.Pandoc.Lua.Module.MediaBag as MediaBag
    import Text.Pandoc.Lua.Module.Utils as Utils

    -- | Parameters used to create lua packages/modules.
    data LuaPackageParams = LuaPackageParams
      { luaPkgCommonState :: CommonState
      , luaPkgDataDir :: Maybe FilePath
      , luaPkgMediaBag :: IORef MediaBag
      }

    -- | Insert pandoc's package loader as the first loader, making it the default.
    installPandocPackageSearcher :: LuaPackageParams -> Lua ()
    installPandocPackageSearcher luaPkgParams = do
      Lua.getglobal' "package.searchers"
      shiftArray
      Lua.pushHaskellFunction (pandocPackageSearcher luaPkgParams)
      Lua.rawseti (Lua.nthFromTop 2) 1
      Lua.pop 1           -- remove 'package.searchers' from stack
     where
      shiftArray = forM_ [4, 3, 2, 1] $ \i -> do
        Lua.rawgeti (-1) i
        Lua.rawseti (-2) (i + 1)

    -- | Load a pandoc module.
    pandocPackageSearcher :: LuaPackageParams -> String -> Lua NumResults
    pandocPackageSearcher luaPkgParams pkgName =
      case pkgName of
        "pandoc"          -> let datadir = luaPkgDataDir luaPkgParams
                             in pushWrappedHsFun (Pandoc.pushModule datadir)
        "pandoc.mediabag" -> let st    = luaPkgCommonState luaPkgParams
                                 mbRef = luaPkgMediaBag luaPkgParams
                             in pushWrappedHsFun (MediaBag.pushModule st mbRef)
        "pandoc.utils"    -> let datadirMb = luaPkgDataDir luaPkgParams
                             in pushWrappedHsFun (Utils.pushModule datadirMb)
        _ -> searchPureLuaLoader
     where
      pushWrappedHsFun f = do
        Lua.pushHaskellFunction f
        return 1
      searchPureLuaLoader = do
        let filename = pkgName ++ ".lua"
        modScript <- liftIO (dataDirScript (luaPkgDataDir luaPkgParams) filename)
        case modScript of
          Just script -> pushWrappedHsFun (loadStringAsPackage pkgName script)
          Nothing -> do
            Lua.push ("no file '" ++ filename ++ "' in pandoc's datadir")
            return 1

    loadStringAsPackage :: String -> ByteString -> Lua NumResults
    loadStringAsPackage pkgName script = do
      status <- Lua.dostring script
      if status == Lua.OK
        then return (1 :: NumResults)
        else do
          msg <- Lua.popValue
          Lua.raiseError ("Error while loading `" <> pkgName <> "`.\n" <> msg)

    -- | Get the ByteString representation of the pandoc module.
    dataDirScript :: Maybe FilePath -> FilePath -> IO (Maybe ByteString)
    dataDirScript datadir moduleFile = do
      res <- runIO $ setUserDataDir datadir >> readDataFile moduleFile
      return $ case res of
        Left _ -> Nothing
        Right s -> Just s