Pandoc.hs

{- |
   Module     : Shakebook.Pandoc
   License    : MIT
   Stability  : experimental

Pandoc utilities lifted to `MonadAction`.
-}
module Shakebook.Pandoc where

import           Control.Comonad
import           Control.Comonad.Cofree
import           Development.Shake.Plus hiding ((:->))
import           RIO
import qualified RIO.ByteString.Lazy    as LBS
import qualified RIO.Text               as T
import           Text.Pandoc.Definition
import           Text.Pandoc.Options
import           Text.Pandoc.PDF
import           Text.Pandoc.Templates
import           Text.Pandoc.Throw
import           Text.Pandoc.Walk
import           Text.Pandoc.Writers

newtype PandocActionException = PandocActionException String
    deriving (Show, Eq, Typeable)

instance Exception PandocActionException where
  displayException (PandocActionException s) = s

-- | Find all the images in a `Pandoc` data structure and call `Development.Shake.Plus.need` on them.
needPandocImagesIn :: (MonadAction m, MonadThrow m) => Path Rel Dir -> Pandoc -> m ()
needPandocImagesIn outDir pdoc =
  mapM parseRelFile (drop 1 . T.unpack <$> pullImages pdoc) >>= needIn outDir where
    pullImages = query f
    f (Image _ _ (src, _)) = [src]
    f _                    = []

-- | Make a pdflatex in an `Action`.
makePDFLaTeX :: (MonadAction m, MonadThrow m) => WriterOptions -> Pandoc -> m LBS.ByteString
makePDFLaTeX wopts p = do
  f <- runPandocIOThrow $ do
    t <- compileDefaultTemplate "latex"
    makePDF "pdflatex" [] writeLaTeX wopts { writerTemplate = Just t } p
  either (throwM . PandocActionException . show) return f

-- | Precarious function that demotes Header numbers within the Pandoc according to its depth
-- in the Cofree. This is so that Headers that H1s that would correctly display for an HTML page
-- will be lower in the table of contents in the PDF equivalent.
progressivelyDemoteHeaders :: Cofree [] Pandoc -> Cofree [] Pandoc
progressivelyDemoteHeaders = pushHeaders 0 where
  handleHeaders :: Int -> Block -> Block
  handleHeaders i (Header a as xs) = Header (max 1 (a + i)) as xs
  handleHeaders _ x                = x

  pushHeaders :: Int -> Cofree [] Pandoc -> Cofree [] Pandoc
  pushHeaders i (x :< xs) = walk (handleHeaders i) x :< map (pushHeaders (i+1)) xs

-- | For a list of file extensions, replace the images with an Inline based on its src path.
replaceUnusableImages :: MonadThrow m => [String] -> (Text -> Inline) -> Pandoc -> m Pandoc
replaceUnusableImages exts f = walkM handleImages where
  handleImages i@(Image _ _ (src, _)) = do
    x <- parseAbsFile (T.unpack src) >>= fileExtension
    return $ if x `elem` exts then f src else i
  handleImages x = return x

-- | Prefix all images in a `Pandoc` with a directory.
prefixAllImages :: Path Rel Dir -> Pandoc -> Pandoc
prefixAllImages dir = walk handleImages where
  handleImages (Image attr ins (src, txt)) = Image attr ins (T.pack (toFilePath dir) <> "/" <> src, txt)
  handleImages x = x