{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE ScopedTypeVariables #-}
{- |
   Module      : Text.Pandoc.Lua.Packages
   Copyright   : Copyright © 2017-2019 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 Foreign.Lua (Lua, NumResults, liftIO)
import Text.Pandoc.Class (readDataFile, runIO, setUserDataDir)

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
  { luaPkgDataDir :: Maybe FilePath
  }

-- | 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 pkgParams pkgName =
  case pkgName of
    "pandoc"          -> let datadir = luaPkgDataDir pkgParams
                         in pushWrappedHsFun (Pandoc.pushModule datadir)
    "pandoc.mediabag" -> pushWrappedHsFun MediaBag.pushModule
    "pandoc.utils"    -> let datadir = luaPkgDataDir pkgParams
                         in pushWrappedHsFun (Utils.pushModule datadir)
    _ -> searchPureLuaLoader
 where
  pushWrappedHsFun f = do
    Lua.pushHaskellFunction f
    return 1
  searchPureLuaLoader = do
    let filename = pkgName ++ ".lua"
    modScript <- liftIO (dataDirScript (luaPkgDataDir pkgParams) filename)
    case modScript of
      Just script -> pushWrappedHsFun (loadStringAsPackage pkgName script)
      Nothing -> do
        Lua.push ("\n\tno 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