Prepare storing the reverse mapping for CMaps, divided by length to be able to implement encoding with a reasonable complexity

src/PDF/CMap.hs

@@ -5,7 +5,6 @@ module PDF.CMap (
     , CMappers
     , CRange(..)
     , cMap
-    , emptyCMap
     , matches
   ) where
 
@@ -21,9 +20,10 @@ import Data.ByteString.Char8.Util (
   )
 import Data.Map (Map, union)
 import qualified Data.Map as Map (
-    adjust, empty, fromList, insertWith, lookup, toList
+    adjust, empty, fromList, insert, insertWith, lookup, toList
   )
 import Data.Text (Text)
+import qualified Data.Text as Text (length)
 import qualified PDF.EOL as EOL (charset, parser)
 import PDF.Font (Decoder, Encoder, Font(..))
 import PDF.Object (
@@ -34,27 +34,29 @@ import PDF.Parser (MonadParser, Parser, runParser, takeAll)
 import Prelude hiding (fail)
 
 type CMappers = Map Name CMap
-data Mapping = Mapping {
-      bsToT :: Map ByteString Text
-    , tToBS :: Map Text ByteString
-  }
+type ToUnicode = Map ByteString Text
+type FromUnicode = Map Text ByteString
 data CRange = CRange {
       fromSequence :: ByteString
     , toSequence :: ByteString
-    , mapping :: Mapping
+    , toUnicode :: ToUnicode
   } deriving Show
-type RangeSize = Int
-type CMap = Map RangeSize [CRange]
+type Size = Int
+data CMap = CMap {
+      toUnicodeBySize :: Map Size [CRange]
+    , fromUnicodeBySize :: Map Size FromUnicode
+  }
 
 toFont :: CMap -> Font
-toFont aCMap = Font {decode = decoder aCMap, encode = encoder aCMap}
+toFont (CMap {toUnicodeBySize, fromUnicodeBySize})  =
+  Font {decode = decoder toUnicodeBySize, encode = encoder fromUnicodeBySize}
 
-decoder :: CMap -> Decoder
-decoder aCMap input
+decoder :: Map Size [CRange] -> Decoder
+decoder rangesBySize input
   | BS.null input = Right ""
   | otherwise = do
-    (output, remainingInput) <- trySizes input $ Map.toList aCMap
-    mappend output <$> decoder aCMap remainingInput
+    (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) =
@@ -64,17 +66,14 @@ decoder aCMap input
         Just outputSequence -> Right (outputSequence, BS.drop size s)
     tryRanges :: ByteString -> [CRange] -> Maybe Text
     tryRanges _ [] = Nothing
-    tryRanges prefix ((CRange {mapping}):cRanges) =
-      case Map.lookup prefix mapping of
+    tryRanges prefix ((CRange {toUnicode}):cRanges) =
+      case Map.lookup prefix toUnicode of
         Nothing -> tryRanges prefix cRanges
         outputSequence -> outputSequence
 
-encoder :: CMap -> Encoder
+encoder :: Map Size FromUnicode -> Encoder
 encoder = undefined
 
-emptyCMap :: CMap
-emptyCMap = Map.empty
-
 matches :: ByteString -> CRange -> Bool
 matches code (CRange {fromSequence, toSequence}) =
   fromSequence <= code && code <= toSequence
@@ -86,6 +85,7 @@ cMap = either fail (return . toFont . snd) . runParser
   where
     ignoredLine =
       takeAll (not . (`elem` EOL.charset)) *> EOL.parser *> return ()
+    emptyCMap = CMap {toUnicodeBySize = Map.empty, fromUnicodeBySize = Map.empty}
 
 codeRanges :: Parser CMap ()
 codeRanges = do
@@ -97,13 +97,14 @@ codeRanges = do
       (,) <$> stringObject <* blank <*> stringObject <* EOL.parser
 
 createMapping :: (StringObject, StringObject) -> Parser CMap ()
-createMapping (Hexadecimal from, Hexadecimal to) = modify $
-  Map.insertWith (++) size [CRange {fromSequence, toSequence, mapping}]
+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
-    mapping = Map.empty
+    cRange = CRange {fromSequence, toSequence, toUnicode = Map.empty}
 createMapping _ = return ()
 
 cMapRange :: Parser CMap ()
@@ -112,32 +113,47 @@ cMapRange = do
   mapM_ saveMapping =<< count size rangeMapping
   line "endbfrange"
   where
-    rangeMapping = (,,) 
-      <$> (stringObject <* blank)
-      <*> (stringObject <* blank)
-      <*> directObject <* EOL.parser
-      >>= mapFromTo
+    rangeMapping = do
+      from <- (stringObject <* blank)
+      to <- (stringObject <* blank)
+      mapFromTo from to =<< directObject <* EOL.parser
 
 saveMapping :: [(ByteString, Text)] -> Parser CMap ()
-saveMapping [] = return ()
-saveMapping assoc@((code, _):_) = modify $ Map.adjust insertCRange mappingSize
+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
-    mappingSize = BS.length code
     appendMapping cRange =
-      cRange {mapping = mapping cRange `union` newMapping}
+      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 =
-      (,) <$> stringObject <* blank <*> stringObject <* EOL.parser
-      >>= pairMapping
+    charMapping = do
+      from <- stringObject <* blank
+      pairMapping from =<< stringObject <* EOL.parser
 
 between :: B16Int -> B16Int -> [ByteString]
 between from@(B16Int s) to =
@@ -149,20 +165,20 @@ 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)) =
+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) =
+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"
+mapFromTo _ _ _ = fail "invalid range mapping found"
 
-pairMapping :: MonadParser m => (StringObject, StringObject) -> m (ByteString, Text)
-pairMapping (Hexadecimal from, Hexadecimal to) =
+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"
+pairMapping _ _ = fail "invalid pair mapping found"