{-# LANGUAGE OverloadedStrings #-}
module PDF.TextRendering (
      TextRendering(..)
    , update
  ) where

import Data.ByteString.Lazy.Char8 (ByteString)
import qualified Data.ByteString.Lazy.Char8 as BS (pack, readInt, unwords, words)

data TextRendering =
    Fill
  | Stroke
  | FillStroke
  | Invisible
  | FillAddPath
  | StrokeAddPath
  | FillStrokeAddPath
  | AddPath
  deriving (Enum, Show)

update :: (TextRendering -> TextRendering) -> ByteString -> ByteString
update f = BS.unwords . changeTextRendering . BS.words
  where
    changeTextRendering :: [ByteString] -> [ByteString]
    changeTextRendering l@[value, "Tr"] =
      case BS.readInt value of
        Just (n, _) -> [BS.pack . show . fromEnum . f $ toEnum n, "Tr"]
        _ -> l
    changeTextRendering l = l