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{-# LANGUAGE FlexibleContexts #-}
{- |
Module : Text.Pandoc.Lua.Filter
Copyright : © 2012–2020 John MacFarlane,
© 2017-2020 Albert Krewinkel
License : GNU GPL, version 2 or above
Maintainer : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
Stability : alpha
Types and functions for running Lua filters.
-}
module Text.Pandoc.Lua.Filter ( LuaFilterFunction
, LuaFilter
, runFilterFile
, walkInlines
, walkBlocks
, module Text.Pandoc.Lua.Walk
) where
import Control.Applicative ((<|>))
import Control.Monad (mplus, (>=>))
import Control.Monad.Catch (finally, try)
import Data.Data (Data, DataType, dataTypeConstrs, dataTypeName, dataTypeOf,
showConstr, toConstr, tyconUQname)
import Data.Foldable (foldrM)
import Data.Map (Map)
import Data.Maybe (fromMaybe)
import Foreign.Lua (Lua, Peekable, Pushable, StackIndex)
import Text.Pandoc.Definition
import Text.Pandoc.Error (PandocError)
import Text.Pandoc.Lua.Marshaling ()
import Text.Pandoc.Lua.Marshaling.List (List (..))
import Text.Pandoc.Lua.Walk (SingletonsList (..))
import Text.Pandoc.Walk (Walkable (walkM))
import qualified Data.Map.Strict as Map
import qualified Foreign.Lua as Lua
import qualified Text.Pandoc.Lua.Util as LuaUtil
-- | Transform document using the filter defined in the given file.
runFilterFile :: FilePath -> Pandoc -> Lua Pandoc
runFilterFile filterPath doc = do
top <- Lua.gettop
stat <- LuaUtil.dofileWithTraceback filterPath
if stat /= Lua.OK
then Lua.throwTopMessage
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 Lua.peek Lua.stackTop
else Lua.pushglobaltable *> fmap (:[]) Lua.popValue
runAll luaFilters doc
runAll :: [LuaFilter] -> Pandoc -> Lua Pandoc
runAll = foldr ((>=>) . walkMWithLuaFilter) return
-- | Filter function stored in the registry
newtype LuaFilterFunction = LuaFilterFunction Lua.Reference
-- | Collection of filter functions (at most one function per element
-- constructor)
newtype LuaFilter = LuaFilter (Map String LuaFilterFunction)
instance Peekable LuaFilter where
peek idx = do
let constrs = listOfInlinesFilterName
: listOfBlocksFilterName
: metaFilterName
: pandocFilterNames
++ blockElementNames
++ inlineElementNames
let go constr acc = do
Lua.getfield idx constr
filterFn <- registerFilterFunction
return $ case filterFn of
Nothing -> acc
Just fn -> Map.insert constr fn acc
LuaFilter <$> foldrM go Map.empty constrs
-- | Register the function at the top of the stack as a filter function in the
-- registry.
registerFilterFunction :: Lua (Maybe LuaFilterFunction)
registerFilterFunction = do
isFn <- Lua.isfunction Lua.stackTop
if isFn
then Just . LuaFilterFunction <$> Lua.ref Lua.registryindex
else Nothing <$ Lua.pop 1
-- | Retrieve filter function from registry and push it to the top of the stack.
pushFilterFunction :: LuaFilterFunction -> Lua ()
pushFilterFunction (LuaFilterFunction fnRef) =
Lua.getref Lua.registryindex fnRef
-- | Fetch either a list of elements from the stack. If there is a single
-- element instead of a list, fetch that element as a singleton list. If the top
-- of the stack is nil, return the default element that was passed to this
-- function. If none of these apply, raise an error.
elementOrList :: Peekable a => a -> Lua [a]
elementOrList x = do
let topOfStack = Lua.stackTop
elementUnchanged <- Lua.isnil topOfStack
if elementUnchanged
then [x] <$ Lua.pop 1
else do
mbres <- peekEither topOfStack
case mbres of
Right res -> [res] <$ Lua.pop 1
Left _ -> Lua.peekList topOfStack `finally` Lua.pop 1
-- | Pop and return a value from the stack; if the value at the top of
-- the stack is @nil@, return the fallback element.
popOption :: Peekable a => a -> Lua a
popOption fallback = fromMaybe fallback . Lua.fromOptional <$> Lua.popValue
-- | Apply filter on a sequence of AST elements. Both lists and single
-- value are accepted as filter function return values.
runOnSequence :: (Data a, Peekable a, Pushable a)
=> LuaFilter -> SingletonsList a -> Lua (SingletonsList a)
runOnSequence (LuaFilter fnMap) (SingletonsList xs) =
SingletonsList <$> mconcatMapM tryFilter xs
where
tryFilter :: (Data a, Peekable a, Pushable a) => a -> Lua [a]
tryFilter x =
let filterFnName = showConstr (toConstr x)
catchAllName = tyconUQname $ dataTypeName (dataTypeOf x)
in case Map.lookup filterFnName fnMap <|> Map.lookup catchAllName fnMap of
Just fn -> runFilterFunction fn x *> elementOrList x
Nothing -> return [x]
-- | Try filtering the given value without type error corrections on
-- the return value.
runOnValue :: (Data a, Peekable a, Pushable a)
=> String -> LuaFilter -> a -> Lua a
runOnValue filterFnName (LuaFilter fnMap) x =
case Map.lookup filterFnName fnMap of
Just fn -> runFilterFunction fn x *> popOption x
Nothing -> return x
-- | 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 :: Pushable a => LuaFilterFunction -> a -> Lua ()
runFilterFunction lf x = do
pushFilterFunction lf
Lua.push x
LuaUtil.callWithTraceback 1 1
walkMWithLuaFilter :: LuaFilter -> Pandoc -> Lua Pandoc
walkMWithLuaFilter f =
walkInlines f
>=> walkInlineLists f
>=> walkBlocks f
>=> walkBlockLists f
>=> walkMeta f
>=> walkPandoc f
mconcatMapM :: (Monad m) => (a -> m [a]) -> [a] -> m [a]
mconcatMapM f = fmap mconcat . mapM f
hasOneOf :: LuaFilter -> [String] -> Bool
hasOneOf (LuaFilter fnMap) = any (\k -> Map.member k fnMap)
contains :: LuaFilter -> String -> Bool
contains (LuaFilter fnMap) = (`Map.member` fnMap)
walkInlines :: Walkable (SingletonsList Inline) a => LuaFilter -> a -> Lua a
walkInlines lf =
let f :: SingletonsList Inline -> Lua (SingletonsList Inline)
f = runOnSequence lf
in if lf `hasOneOf` inlineElementNames
then walkM f
else return
walkInlineLists :: Walkable (List Inline) a => LuaFilter -> a -> Lua a
walkInlineLists lf =
let f :: List Inline -> Lua (List Inline)
f = runOnValue listOfInlinesFilterName lf
in if lf `contains` listOfInlinesFilterName
then walkM f
else return
walkBlocks :: Walkable (SingletonsList Block) a => LuaFilter -> a -> Lua a
walkBlocks lf =
let f :: SingletonsList Block -> Lua (SingletonsList Block)
f = runOnSequence lf
in if lf `hasOneOf` blockElementNames
then walkM f
else return
walkBlockLists :: Walkable (List Block) a => LuaFilter -> a -> Lua a
walkBlockLists lf =
let f :: List Block -> Lua (List Block)
f = runOnValue listOfBlocksFilterName lf
in if lf `contains` listOfBlocksFilterName
then walkM f
else return
walkMeta :: LuaFilter -> Pandoc -> Lua Pandoc
walkMeta lf (Pandoc m bs) = do
m' <- runOnValue "Meta" lf m
return $ Pandoc m' bs
walkPandoc :: LuaFilter -> Pandoc -> Lua Pandoc
walkPandoc (LuaFilter fnMap) =
case foldl mplus Nothing (map (`Map.lookup` fnMap) pandocFilterNames) of
Just fn -> \x -> runFilterFunction fn x *> singleElement x
Nothing -> return
constructorsFor :: DataType -> [String]
constructorsFor x = map show (dataTypeConstrs x)
inlineElementNames :: [String]
inlineElementNames = "Inline" : constructorsFor (dataTypeOf (Str mempty))
blockElementNames :: [String]
blockElementNames = "Block" : constructorsFor (dataTypeOf (Para []))
listOfInlinesFilterName :: String
listOfInlinesFilterName = "Inlines"
listOfBlocksFilterName :: String
listOfBlocksFilterName = "Blocks"
metaFilterName :: String
metaFilterName = "Meta"
pandocFilterNames :: [String]
pandocFilterNames = ["Pandoc", "Doc"]
singleElement :: Peekable a => a -> Lua a
singleElement x = do
elementUnchanged <- Lua.isnil (-1)
if elementUnchanged
then x <$ Lua.pop 1
else do
mbres <- peekEither (-1)
case mbres of
Right res -> res <$ Lua.pop 1
Left err -> do
Lua.pop 1
Lua.throwMessage
("Error while trying to get a filter's return " <>
"value from Lua stack.\n" <> show err)
-- | Try to convert the value at the given stack index to a Haskell value.
-- Returns @Left@ with an error message on failure.
peekEither :: Peekable a => StackIndex -> Lua (Either PandocError a)
peekEither = try . Lua.peek
|