{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
module PDF.Content.Text (
      Chunks(..)
    , format
    , renderText
  ) where

import Control.Monad (foldM)
import Control.Monad.Fail (MonadFail(..))
import Control.Monad.Reader (MonadReader(..), ReaderT, asks, runReaderT)
import Control.Monad.State (MonadState(..), StateT, evalStateT)
import Data.Id (Id(..), Indexed)
import Data.Map ((!))
import qualified Data.Map as Map (empty, singleton)
import Data.Text (Text, breakOn)
import qualified Data.Text as Text (drop)
import PDF.Box (Box(..))
import PDF.Content (
      Content, ContentUnit(..), GraphicContextUnit(..), contentUnits
  )
import qualified PDF.Content as Content (Content(..))
import PDF.Content.Operator (Instruction, Operator(..))
import PDF.Content.Operator.Text (Operator(..))
import PDF.Font (Font(..), FontSet, emptyFont)
import PDF.Object (DirectObject(..), StringObject(..), toByteString)
import Prelude hiding (fail)

data ROContext = ROContext {
      indexedInstructions :: Indexed Instruction
    , fontSet :: FontSet
  }

type TextContent m = ReaderT ROContext m
type FontContext m = StateT Font (TextContent m)

decodeString :: MonadFail m => StringObject -> FontContext m Text
decodeString input = do
  Font {decode} <- get
  either fail return . decode $ toByteString input

data Chunks = Chunks

instance MonadFail m => Box (ReaderT FontSet m) Chunks Content (Indexed Text) where
  r Chunks content = do
    fontSet <- ask
    renderText fontSet content

renderText :: MonadFail m => FontSet -> Content -> m (Indexed Text)
renderText fontSet (Content.Content {contentUnits, Content.indexedInstructions}) =
  runReaderT (mconcat <$> mapM renderContentUnit contentUnits) roContext
  where
    roContext = ROContext {indexedInstructions, fontSet}

renderContentUnit :: MonadFail m => ContentUnit -> TextContent m (Indexed Text)
renderContentUnit (GraphicContext graphicContextUnits) =
  mconcat <$> mapM renderGraphicContextUnit graphicContextUnits
renderContentUnit (TextContext instructionIds) =
  evalStateT (mconcat <$> mapM renderInstructionId instructionIds) emptyFont

renderGraphicContextUnit :: MonadFail m => GraphicContextUnit -> TextContent m (Indexed Text)
renderGraphicContextUnit (GraphicInstruction _) = return Map.empty
renderGraphicContextUnit (ContentUnit contentUnit) =
  renderContentUnit contentUnit

renderInstructionId :: MonadFail m => Id Instruction -> FontContext m (Indexed Text)
renderInstructionId instructionId@(Id n) = toMap <$>
  (asks ((! instructionId) . indexedInstructions) >>= renderInstruction)
  where
    toMap = maybe Map.empty (Map.singleton (Id n))

renderInstruction :: MonadFail m => Instruction -> FontContext m (Maybe Text)
renderInstruction (Text Tf, [NameObject fontName, _]) =
  asks ((! fontName) . fontSet) >>= put >> return Nothing

renderInstruction (Text Tstar, []) = return $ Just "\n"

renderInstruction (Text TJ, [Array arrayObject]) =
  Just <$> foldM appendText "" arrayObject
  where
    appendText t (StringObject outputString) =
      mappend t <$> decodeString outputString
    appendText t _ = return t

renderInstruction (Text Tj, [StringObject outputString]) =
  Just <$> decodeString outputString

renderInstruction (Text Quote, [StringObject outputString]) =
  (Just . mappend "\n") <$> decodeString outputString

renderInstruction (Text DQuote, [_, _, StringObject outputString]) =
  (Just . mappend "\n") <$> decodeString outputString

renderInstruction _ = return Nothing

format :: (MonadFail m, MonadReader Font m) => Text -> m [Instruction]
format input =
  case breakOn "\n" input of
    ("", "") -> return []
    ("", left) -> ((Text Tstar, []) :) <$> format (Text.drop 1 left)
    (line, left) -> (:) <$> tj line <*> format left
  where
    tj t = do
      literal <- either fail (return . Literal) =<< asks (($t) . encode)
      return (Text Tj, [StringObject literal])