{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE FlexibleContexts #-}
module PDF.CMap (
      CMap
    , CMappers
    , CRange(..)
    , matches
    , parse
  ) where

import Control.Applicative ((<|>), many)
import Control.Monad.Except (MonadError(..))
import Control.Monad.Fail (fail)
import Control.Monad.State (modify)
import Data.Attoparsec.ByteString.Char8 (count)
import Data.ByteString (ByteString)
import qualified Data.ByteString as BS (drop, length, null, take)
import Data.ByteString.Char8 (unpack)
import Data.ByteString.Char8.Util (
    B16Int(..), b16ToBytes, b16ToInt, toBytes, utf16BEToutf8
  )
import Data.Foldable (foldl', foldr')
import Data.Map (Map, mapWithKey, union)
import qualified Data.Map as Map (
    adjust, empty, fromList, insert, insertWith, lookup, toList
  )
import Data.Text (Text)
import qualified Data.Text as Text (length, null, splitAt)
import qualified PDF.EOL as EOL (charset, parser)
import PDF.Font (Decoder, Encoder, Font(..))
import PDF.Object (
      DirectObject(..), Name, StringObject(..)
    , blank, directObject, integer, line, stringObject
  )
import PDF.Parser (MonadParser, Parser, runParser, takeAll)
import Prelude hiding (fail)

type CMappers = Map Name CMap
type ToUnicode = Map ByteString Text
type FromUnicode = Map Text ByteString
data CRange = CRange {
      fromSequence :: ByteString
    , toSequence :: ByteString
    , toUnicode :: ToUnicode
  } deriving Show
type Size = Int
data CMap = CMap {
      toUnicodeBySize :: Map Size [CRange]
    , fromUnicodeBySize :: Map Size FromUnicode
  }

toFont :: CMap -> Font
toFont (CMap {toUnicodeBySize, fromUnicodeBySize})  =
  Font {decode = decoder toUnicodeBySize, encode = encoder fromUnicodeBySize}

decoder :: Map Size [CRange] -> Decoder
decoder rangesBySize input
  | BS.null input = Right ""
  | otherwise = do
    (output, remainingInput) <- trySizes input $ Map.toList rangesBySize
    mappend output <$> decoder rangesBySize remainingInput
  where
    trySizes s [] = Left $ "No matching code found in font for " ++ unpack s
    trySizes s ((size, cRanges):others) =
      let prefix = BS.take size s in
      case tryRanges prefix cRanges of
        Nothing -> trySizes s others
        Just outputSequence -> Right (outputSequence, BS.drop size s)
    tryRanges :: ByteString -> [CRange] -> Maybe Text
    tryRanges _ [] = Nothing
    tryRanges prefix ((CRange {toUnicode}):cRanges) =
      case Map.lookup prefix toUnicode of
        Nothing -> tryRanges prefix cRanges
        outputSequence -> outputSequence

encoder :: Map Size FromUnicode -> Encoder
encoder fromUnicodes input
  | Text.null input = Right ""
  | otherwise =
    foldr' (<>) (Left "No encoding found") $ mapWithKey tryOn fromUnicodes
    where
      tryOn size fromUnicode =
        let (prefix, end) = Text.splitAt size input in
        case Map.lookup prefix fromUnicode of
          Nothing -> Left ""
          Just code -> (code <>) <$> encoder fromUnicodes end

matches :: ByteString -> CRange -> Bool
matches code (CRange {fromSequence, toSequence}) =
  fromSequence <= code && code <= toSequence

parse :: MonadError String m => ByteString -> m Font
parse = either throwError (return . toFont . snd) . runParser
  (many (codeRanges <|> cMapRange <|> cMapChar <|> ignoredLine))
  emptyCMap
  where
    ignoredLine =
      takeAll (not . (`elem` EOL.charset)) *> EOL.parser *> return ()
    emptyCMap = CMap {toUnicodeBySize = Map.empty, fromUnicodeBySize = Map.empty}

codeRanges :: Parser CMap ()
codeRanges = do
  size <- integer <* line "begincodespacerange"
  mapM_ createMapping =<< count size codeRange
  line "endcodespacerange"
  where
    codeRange =
      (,) <$> stringObject <* blank <*> stringObject <* EOL.parser

createMapping :: (StringObject, StringObject) -> Parser CMap ()
createMapping (Hexadecimal from, Hexadecimal to) = modify $ \cmap -> cmap {
      toUnicodeBySize = Map.insertWith (++) size [cRange] (toUnicodeBySize cmap)
    }
  where
    fromSequence = b16ToBytes from
    size = BS.length fromSequence
    toSequence = b16ToBytes to
    cRange = CRange {fromSequence, toSequence, toUnicode = Map.empty}
createMapping _ = return ()

cMapRange :: Parser CMap ()
cMapRange = do
  size <- integer <* line "beginbfrange"
  mapM_ saveMapping =<< count size rangeMapping
  line "endbfrange"
  where
    rangeMapping = do
      from <- (stringObject <* blank)
      to <- (stringObject <* blank)
      mapFromTo from to =<< directObject <* EOL.parser

saveMapping :: [(ByteString, Text)] -> Parser CMap ()
saveMapping assoc =
  modify $ \(CMap {toUnicodeBySize, fromUnicodeBySize}) -> CMap {
        toUnicodeBySize = saveToUnicodeBySize assoc toUnicodeBySize
      , fromUnicodeBySize = saveFromUnicodeBySize reversed fromUnicodeBySize
    }
    where
      reversed = (\(a, b) -> (b, a)) <$> assoc

saveToUnicodeBySize :: [(ByteString, Text)] -> Map Size [CRange] -> Map Size [CRange]
saveToUnicodeBySize [] = id
saveToUnicodeBySize assoc@((code, _):_) = Map.adjust insertCRange (BS.length code)
  where
    newMapping = Map.fromList assoc
    appendMapping cRange =
      cRange {toUnicode = toUnicode cRange `union` newMapping}
    insertCRange = fmap (\cRange ->
        if code `matches` cRange then appendMapping cRange else cRange
      )

saveFromUnicodeBySize :: [(Text, ByteString)] -> Map Size FromUnicode -> Map Size FromUnicode
saveFromUnicodeBySize = flip (foldl' insertFromUnicode)
  where
    insertFromUnicode :: Map Size FromUnicode -> (Text, ByteString) -> Map Size FromUnicode
    insertFromUnicode tmpFromUnicodeBySize (unicodeSequence, code) =
      let size = Text.length unicodeSequence in
      Map.adjust (Map.insert unicodeSequence code) size tmpFromUnicodeBySize

cMapChar :: Parser CMap ()
cMapChar = do
  size <- integer <* line "beginbfchar"
  saveMapping =<< count size charMapping <* line "endbfchar"
  where
    charMapping = do
      from <- stringObject <* blank
      pairMapping from =<< stringObject <* EOL.parser

between :: B16Int -> B16Int -> [ByteString]
between from@(B16Int s) to =
  let size = BS.length s `div` 2 in
  toBytes size <$> [b16ToInt from .. b16ToInt to]

startFrom :: B16Int -> [ByteString]
startFrom from@(B16Int s) =
  let size = BS.length s `div` 2 in
  toBytes size <$> [b16ToInt from .. ]

mapFromTo :: MonadParser m => StringObject -> StringObject -> DirectObject -> m [(ByteString, Text)]
mapFromTo (Hexadecimal from) (Hexadecimal to) (StringObject (Hexadecimal dstFrom)) =
  return $ zip (between from to) (utf16BEToutf8 <$> startFrom dstFrom)

mapFromTo (Hexadecimal from) (Hexadecimal to) (Array dstPoints) =
  zip (between from to) <$> (mapM dstByteString dstPoints)
  where
    dstByteString (StringObject (Hexadecimal dst)) =
      return . utf16BEToutf8 $ b16ToBytes dst
    dstByteString _ = fail "Invalid for a replacement string"

mapFromTo _ _ _ = fail "invalid range mapping found"

pairMapping :: MonadParser m => StringObject -> StringObject -> m (ByteString, Text)
pairMapping (Hexadecimal from) (Hexadecimal to) =
  return (b16ToBytes  from, utf16BEToutf8 $ b16ToBytes  to)
pairMapping _ _ = fail "invalid pair mapping found"