{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

import Control.Monad.Fail (MonadFail(..))
import Control.Monad.Reader (ReaderT, runReaderT)
import Data.ByteString.Lazy.Char8 (ByteString)
import qualified Data.ByteString.Char8 as BS (readFile)
import qualified Data.ByteString.Lazy.Char8 as Lazy (putStrLn)
import Data.Id (Id(..))
import PDF (Document(..), parseDocument)
import PDF.Box (Box(..))
import PDF.Layer (Layer(..), unify)
import PDF.Object (Object(..))
import PDF.Object.Navigation (
    Clear(..), Raw(..), (//), objectById, origin
  )
import PDF.Output (Output)
import qualified PDF.Output as Output (render)
import Prelude hiding (fail)
import System.Environment (getArgs, getProgName)
import System.Exit (die)
import Text.Printf (printf)
import Text.Read (readMaybe)

newtype Error a = Error {
    runError :: Either String a
  } deriving (Functor, Applicative, Monad)
instance MonadFail Error where
  fail = Error . Left

decodedStream :: Object -> Object
decodedStream object =
  maybe object id $ r Clear object >>= flip (w Raw) object

display :: Output a => ReaderT Layer Error a -> Document -> Either String ByteString
display getter (Document {eolStyle, layers}) =
  Output.render eolStyle <$> runError (runReaderT getter (unify layers))

parse :: [String] -> IO (FilePath, Document -> Either String ByteString)
parse [inputFile] = return (inputFile, display origin)
parse [inputFile, key] =
  return (inputFile, clear . maybe (byPath key) byId $ readMaybe key)
  where
    byId = objectById . Id
    byPath path = origin // (explode path)
    explode "" = []
    explode path =
      case break (== '.') path of
        (name, "") -> [name]
        (name, rest) -> name : explode (drop 1 rest)
    clear = display . fmap decodedStream
parse _ =
  die . printf "Syntax: %s inputFile [OBJECT_ID | PATH_TO_OBJ]\n" =<< getProgName

main :: IO ()
main = do
  (inputFile, getData) <- parse =<< getArgs
  input <- BS.readFile inputFile
  either die Lazy.putStrLn $ (parseDocument input >>= getData)