{-# LANGUAGE CPP               #-}
{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE TemplateHaskell   #-}
{-# LANGUAGE OverloadedStrings #-}
{- |
   Module      : Text.Pandoc.Filter
   Copyright   : Copyright (C) 2006-2019 John MacFarlane
   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley@edu>
   Stability   : alpha
   Portability : portable

Programmatically modifications of pandoc documents.
-}
module Text.Pandoc.Filter
  ( Filter (..)
  , applyFilters
  ) where

import Prelude
import Data.Aeson.TH (deriveJSON, defaultOptions)
import GHC.Generics (Generic)
import Text.Pandoc.Class (PandocIO)
import Text.Pandoc.Definition (Pandoc)
import Text.Pandoc.Options (ReaderOptions)
import qualified Text.Pandoc.Filter.JSON as JSONFilter
import qualified Text.Pandoc.Filter.Lua as LuaFilter
import qualified Text.Pandoc.Filter.Path as Path
import Data.YAML
import qualified Data.Text as T
import System.FilePath (takeExtension)
import Control.Applicative ((<|>))
import Control.Monad (foldM)

-- | Type of filter and path to filter file.
data Filter = LuaFilter FilePath
            | JSONFilter FilePath
            deriving (Show, Generic)

instance FromYAML Filter where
 parseYAML node =
  (withMap "Filter" $ \m -> do
    ty <- m .: "type"
    fp <- m .: "path"
    case ty of
      "lua"  -> return $ LuaFilter $ T.unpack fp
      "json" -> return $ JSONFilter $ T.unpack fp
      _      -> fail $ "Unknown filter type " ++ show (ty :: T.Text)) node
  <|>
  (withStr "Filter" $ \t -> do
    let fp = T.unpack t
    case takeExtension fp of
      ".lua"  -> return $ LuaFilter fp
      _       -> return $ JSONFilter fp) node

-- | Modify the given document using a filter.
applyFilters :: ReaderOptions
             -> [Filter]
             -> [String]
             -> Pandoc
             -> PandocIO Pandoc
applyFilters ropts filters args d = do
  expandedFilters <- mapM expandFilterPath filters
  foldM applyFilter d expandedFilters
 where
  applyFilter doc (JSONFilter f) = JSONFilter.apply ropts args f doc
  applyFilter doc (LuaFilter f)  = LuaFilter.apply ropts args f doc

-- | Expand paths of filters, searching the data directory.
expandFilterPath :: Filter -> PandocIO Filter
expandFilterPath (LuaFilter fp) = LuaFilter <$> Path.expandFilterPath fp
expandFilterPath (JSONFilter fp) = JSONFilter <$> Path.expandFilterPath fp

$(deriveJSON defaultOptions ''Filter)