{-# LANGUAGE CPP                   #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
{-
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

Pandoc lua utils.
-}
module Text.Pandoc.Lua (LuaException (..), pushPandocModule, runLuaFilter) where

import Control.Monad (mplus, unless, when, (>=>))
import Control.Monad.Identity (Identity)
import Control.Monad.Trans (MonadIO (..))
import Data.Data (DataType, Data, toConstr, showConstr, dataTypeOf,
                  dataTypeConstrs, dataTypeName, tyconUQname)
import Data.Foldable (foldrM)
import Data.Map (Map)
import Data.Maybe (isJust)
import Foreign.Lua (Lua, FromLuaStack (peek), LuaException (..), StackIndex,
                    Status (OK), ToLuaStack (push))
import Text.Pandoc.Definition
import Text.Pandoc.Lua.PandocModule (pushPandocModule)
import Text.Pandoc.Walk (walkM)

import qualified Data.Map as Map
import qualified Foreign.Lua as Lua

runLuaFilter :: (MonadIO m)
             => Maybe FilePath -> FilePath -> String -> Pandoc -> m Pandoc
runLuaFilter datadir filterPath format pd = liftIO . Lua.runLua $ do
  Lua.openlibs
  -- store module in global "pandoc"
  pushPandocModule datadir
  Lua.setglobal "pandoc"
  push format
  Lua.setglobal "FORMAT"
  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 implicitly defined global filter if nothing was returned
      when (newtop - top < 1) pushGlobalFilter
      luaFilters <- peek (-1)
      runAll luaFilters pd

pushGlobalFilter :: Lua ()
pushGlobalFilter = do
  Lua.newtable
  Lua.getglobal' "pandoc.global_filter"
  Lua.call 0 1
  Lua.rawseti (-2) 1

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

walkMWithLuaFilter :: LuaFilter -> Pandoc -> Lua Pandoc
walkMWithLuaFilter (LuaFilter fnMap) =
  walkInlines >=> walkBlocks >=> walkMeta >=> walkPandoc
 where
    walkInlines :: Pandoc -> Lua Pandoc
    walkInlines =
      if hasOneOf inlineFilterNames
      then walkM (mconcatMapM (tryFilter fnMap :: Inline -> Lua [Inline]))
      else return

    walkBlocks :: Pandoc -> Lua Pandoc
    walkBlocks =
      if hasOneOf blockFilterNames
      then walkM (mconcatMapM (tryFilter fnMap :: Block -> Lua [Block]))
      else return

    walkMeta :: Pandoc -> Lua Pandoc
    walkMeta =
      case Map.lookup "Meta" fnMap of
        Just fn -> walkM (\(Pandoc meta blocks) -> do
                             meta' <- runFilterFunction fn meta *> singleElement meta
                             return $ Pandoc meta' blocks)
        Nothing -> return

    walkPandoc :: Pandoc -> Lua Pandoc
    walkPandoc =
      case foldl mplus Nothing (map (`Map.lookup` fnMap) pandocFilterNames) of
        Just fn -> \x -> runFilterFunction fn x *> singleElement x
        Nothing -> return

    mconcatMapM f = fmap mconcat . mapM f
    hasOneOf = any (\k -> isJust (Map.lookup k fnMap))

constructorsFor :: DataType -> [String]
constructorsFor x = map show (dataTypeConstrs x)

inlineFilterNames :: [String]
inlineFilterNames = "Inline" : constructorsFor (dataTypeOf (Str []))

blockFilterNames :: [String]
blockFilterNames = "Block" : constructorsFor (dataTypeOf (Para []))

metaFilterName :: String
metaFilterName = "Meta"

pandocFilterNames :: [String]
pandocFilterNames = ["Pandoc", "Doc"]

type FunctionMap = Map String LuaFilterFunction
newtype LuaFilter = LuaFilter FunctionMap
newtype LuaFilterFunction = LuaFilterFunction { functionIndex :: Int }

-- | Try running a filter for the given element
tryFilter :: (Data a, FromLuaStack a, ToLuaStack a)
          => FunctionMap -> a -> Lua [a]
tryFilter fnMap x =
  let filterFnName = showConstr (toConstr x)
      catchAllName = tyconUQname $ dataTypeName (dataTypeOf x)
  in
  case Map.lookup filterFnName fnMap `mplus` Map.lookup catchAllName fnMap of
    Just fn -> runFilterFunction fn x *> elementOrList x
    Nothing -> return [x]

instance FromLuaStack LuaFilter where
  peek idx =
    let constrs = metaFilterName : pandocFilterNames
                  ++ blockFilterNames
                  ++ inlineFilterNames
        fn c acc = do
          Lua.getfield idx c
          filterFn <- Lua.tryLua (peek (-1))
          Lua.pop 1
          return $ case filterFn of
            Left _ -> acc
            Right f -> (c, f) : acc
    in LuaFilter . Map.fromList <$> foldrM fn [] constrs

-- | Push a value to the stack via a lua filter function. The filter function is
-- called with given element as argument and is expected to return an element.
-- Alternatively, the function can return nothing or nil, in which case the
-- element is left unchanged.
runFilterFunction :: ToLuaStack a => LuaFilterFunction -> a -> Lua ()
runFilterFunction lf x = do
  pushFilterFunction lf
  push x
  z <- Lua.pcall 1 1 Nothing
  when (z /= OK) $ do
    msg <- Lua.peek (-1) <* Lua.pop 1
    let prefix = "Error while running filter function: "
    Lua.throwLuaError $ prefix ++ msg

elementOrList :: FromLuaStack a => a -> Lua [a]
elementOrList x = do
  let topOfStack = Lua.StackIndex (-1)
  elementUnchanged <- Lua.isnil topOfStack
  if elementUnchanged
    then [x] <$ Lua.pop 1
    else do
       mbres <- Lua.peekEither topOfStack
       case mbres of
         Right res -> [res] <$ Lua.pop 1
         Left _  -> Lua.toList topOfStack <* Lua.pop 1

singleElement :: FromLuaStack a => a -> Lua a
singleElement x = do
  elementUnchanged <- Lua.isnil (-1)
  if elementUnchanged
    then x <$ Lua.pop 1
    else do
    mbres <- Lua.peekEither (-1)
    case mbres of
      Right res -> res <$ Lua.pop 1
      Left err  -> do
        Lua.pop 1
        Lua.throwLuaError $
          "Error while trying to get a filter's return " ++
          "value from lua stack.\n" ++ err

-- | Push the filter function to the top of the stack.
pushFilterFunction :: LuaFilterFunction -> Lua ()
pushFilterFunction lf =
  -- The function is stored in a lua registry table, retrieve it from there.
  Lua.rawgeti Lua.registryindex (functionIndex lf)

registerFilterFunction :: StackIndex -> Lua LuaFilterFunction
registerFilterFunction idx = do
  isFn <- Lua.isfunction idx
  unless isFn . Lua.throwLuaError $ "Not a function at index " ++ show idx
  Lua.pushvalue idx
  refIdx <- Lua.ref Lua.registryindex
  return $ LuaFilterFunction refIdx

instance (FromLuaStack a) => FromLuaStack (Identity a) where
  peek = fmap return . peek

instance ToLuaStack LuaFilterFunction where
  push = pushFilterFunction

instance FromLuaStack LuaFilterFunction where
  peek = registerFilterFunction