Lua filters: refactor lua module handling

The integration with Lua's package/module system is improved: A
pandoc-specific package searcher is prepended to the searchers in
`package.searchers`. The modules `pandoc` and `pandoc.mediabag` can now
be loaded via `require`.

1 files changed, 109 insertions, 0 deletions

diff --git a/src/Text/Pandoc/Lua/Packages.hs b/src/Text/Pandoc/Lua/Packages.hs
new file mode 100644
index 000000000..ede7beccd
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Packages.hs
@@ -0,0 +1,109 @@
+{-
+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
+-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE FlexibleContexts #-}
+{- |
+   Module      : Text.Pandoc.Lua.Packages
+   Copyright   : Copyright © 2017 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 Control.Monad (forM_)
+import Data.ByteString.Char8 (unpack)
+import Data.IORef (IORef)
+import Foreign.Lua (Lua, NumResults, liftIO)
+import Text.Pandoc.Class (CommonState, readDataFile, runIO, setUserDataDir)
+import Text.Pandoc.MediaBag (MediaBag)
+import Text.Pandoc.Lua.PandocModule (pushPandocModule, pushMediaBagModule)
+import Text.Pandoc.Lua.Util (dostring')
+
+import qualified Foreign.Lua as Lua
+
+-- | 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.wrapHaskellFunction
+  Lua.rawseti (-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 (pushPandocModule datadir)
+    "pandoc.mediabag" -> let st    = luaPkgCommonState luaPkgParams
+                             mbRef = luaPkgMediaBag luaPkgParams
+                         in pushWrappedHsFun (pushMediaBagModule st mbRef)
+    _ -> searchPureLuaLoader
+ where
+  pushWrappedHsFun f = do
+    Lua.pushHaskellFunction f
+    Lua.wrapHaskellFunction
+    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 -> String -> Lua NumResults
+loadStringAsPackage pkgName script = do
+  status <- dostring' script
+  if status == Lua.OK
+    then return (1 :: NumResults)
+    else do
+      msg <- Lua.peek (-1) <* Lua.pop 1
+      Lua.push ("Error while loading ``" ++ pkgName ++ "`.\n" ++ msg)
+      Lua.lerror
+      return (2 :: NumResults)
+
+-- | Get the string representation of the pandoc module
+dataDirScript :: Maybe FilePath -> FilePath -> IO (Maybe String)
+dataDirScript datadir moduleFile = do
+  res <- runIO $ setUserDataDir datadir >> readDataFile moduleFile
+  return $ case res of
+    Left _ -> Nothing
+    Right s -> Just (unpack s)
+