{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
module PDF.Content (
      Content(..)
    , ContentUnit(..)
    , GraphicContextUnit(..)
    , TextContext
    , parse
  ) where

import Control.Applicative ((<|>))
import Control.Monad.Fail (MonadFail)
import Control.Monad.Reader (asks, runReader)
import Control.Monad.State (evalStateT, modify)
import Data.Attoparsec.ByteString.Char8 (sepBy)
import Data.ByteString (ByteString)
import Data.Id (Id(..), Indexed, at, empty, register)
import PDF.Box (Box(..))
import PDF.Content.Operator (Instruction, operator)
import PDF.Object (blank, directObject)
import PDF.Output (Output(..), line)
import PDF.Parser (Parser, runParser, string)

data Instructions = Instructions

data GraphicContextUnit =
    GraphicInstruction (Id Instruction)
  | ContentUnit ContentUnit
  deriving Show
type TextContext = [Id Instruction]
data ContentUnit =
    GraphicContext [GraphicContextUnit]
  | TextContext TextContext
  deriving Show
data Content = Content {
      contentUnits :: [ContentUnit]
    , indexedInstructions :: Indexed Instruction
  } deriving Show

type InstructionParser = Parser (Indexed Instruction)

instance Monad m => Box m Instructions Content (Indexed Instruction) where
  r Instructions = return . indexedInstructions
  w Instructions indexedInstructions someContent =
    return $ someContent {indexedInstructions}

parse :: MonadFail m => ByteString -> m Content
parse =
  either fail (return . uncurry Content) . runParser contentUnits empty
  where
    contentUnits = contentUnit `sepBy` blank

contentUnit :: InstructionParser ContentUnit
contentUnit =
    (GraphicContext <$> graphicContext)
  <|> (TextContext <$> textContext)
  where
    graphicContext =
      string "q" *> blank *> graphicContextUnit `sepBy` blank <* blank <* string "Q"

graphicContextUnit :: InstructionParser GraphicContextUnit
graphicContextUnit =
    (GraphicInstruction <$> instruction)
  <|> (ContentUnit <$> contentUnit)

instruction :: InstructionParser (Id Instruction)
instruction = evalStateT stackParser [] >>= register
  where
    stackParser = ((directObject <* blank) >>= push) <|> operator
    push arg = modify (arg:) *> stackParser

textContext :: InstructionParser TextContext
textContext =
  string "BT" *> blank *> instruction `sepBy` blank <* blank <* string "ET"

instance Output Content where
  output (Content {contentUnits, indexedInstructions}) =
    runReader (mconcat <$> mapM outputCU contentUnits) indexedInstructions
    where
      outputCU (GraphicContext gc) = do
        inside <- mconcat <$> mapM outputGCU gc
        return (line "q" `mappend` inside `mappend` line "Q")
      outputCU (TextContext tc) = do
        inside <- mconcat <$> mapM outputIId tc
        return (line "BT" `mappend` inside `mappend` line "ET")
      outputGCU (GraphicInstruction gi) = outputIId gi
      outputGCU (ContentUnit cu) = outputCU cu
      outputIId instructionId = asks (output . (`at` instructionId))