Reimplement getObj with the newest tools in PDF.Object.Navigation, in particular implement browsing by paths or random objectId access

Hufflepdf.cabal

@@ -65,7 +65,7 @@ executable             getObj
                      , bytestring
                      , containers
                      , Hufflepdf
-                     , zlib
+                     , mtl
   ghc-options:         -Wall
   default-language:    Haskell2010
 

examples/getObj.hs

@@ -1,53 +1,51 @@
 {-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE FlexibleContexts #-}
 
-import Codec.Compression.Zlib (decompress)
+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 (fromStrict, putStr, toStrict)
-import Data.Map ((!?))
-import qualified Data.Map as Map (keys, lookup)
+import qualified Data.ByteString.Lazy.Char8 as Lazy (putStrLn)
 import PDF (Document(..), parseDocument)
-import qualified PDF.EOL as EOL (Style)
-import PDF.Object (Content(..), DirectObject(..), Object(..), Name(..))
-import PDF.Output (ObjectId(..))
+import PDF.Object (Content(..), Object(..))
+import PDF.Object.Navigation (
+    Error(..), (//), castObject, objectById, openStream, origin
+  )
+import PDF.Output (ObjectId(..), Output)
 import qualified PDF.Output as Output (render)
 import PDF.Update (unify)
 import System.Environment (getArgs, getProgName)
 import System.Exit (die)
 import Text.Printf (printf)
+import Text.Read (readMaybe)
 
-display :: EOL.Style -> Object -> ByteString
-display eolStyle d@(Direct _) = Output.render eolStyle d
-display eolStyle s@(Stream {header, streamContent}) = Output.render eolStyle $
-  case Map.lookup (Name "Filter") header of
-    Just (NameObject (Name "FlateDecode")) -> Stream {
-          header
-        , streamContent = Lazy.toStrict . decompress $ Lazy.fromStrict streamContent
-      }
-    _ -> s
-
-extractObject :: ObjectId -> Document -> Either String ByteString
-extractObject objectId (Document {eolStyle, updates}) =
-  case objects content !? objectId of
-    Nothing -> Left $ "No object has ID " ++ show (getObjectId objectId)
-    Just o -> Right $ display eolStyle o
+decodedStream :: Object -> Object
+decodedStream object =
+  maybe object replaceContent $ openStream object
   where
-    content = unify updates
+    replaceContent streamContent = object {streamContent}
 
-listObjectIds :: Document -> Either String [String]
-listObjectIds =
-  Right . prependTitle . toString . Map.keys . objects . unify . updates
+display :: Output a => ReaderT Content Error a -> Document -> Either String ByteString
+display getter (Document {eolStyle, updates}) =
+  Output.render eolStyle <$> runError (runReaderT getter (unify updates))
+
+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
-    toString = fmap (show . getObjectId)
-    prependTitle = ("ObjectIds defined in this PDF:":)
+    byId = objectById . ObjectId
+    byPath path = (origin >>= (// (explode path)) >>= castObject)
+    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 id $ (parseDocument input >>= getData)
-  where
-    parse [inputFile] = return (inputFile, fmap (mapM_ putStrLn) . listObjectIds)
-    parse [inputFile, objectId] = return
-      (inputFile, fmap Lazy.putStr . extractObject (ObjectId (read objectId)))
-    parse _ = die . printf "Syntax: %s inputFile [OBJECT_ID]\n" =<< getProgName
+  either die Lazy.putStrLn $ (parseDocument input >>= getData)

src/PDF/Object/Navigation.hs

@@ -5,6 +5,7 @@
 module PDF.Object.Navigation (
       Error(..)
     , (//)
+    , castObject
     , dictionaryById
     , getDictionary
     , getField
@@ -43,6 +44,10 @@ castDictionary (Direct (Dictionary aDict)) = return aDict
 castDictionary (Stream {header}) = return header
 castDictionary obj = expected "dictionary : " obj
 
+castObject :: PDFContent m => DirectObject -> m Object
+castObject directObject =
+  (castObjectId directObject >>= objectById) <|> return (Direct directObject)
+
 castObjectId :: MonadFail m => DirectObject -> m ObjectId
 castObjectId (Reference (IndirectObjCoordinates {objectId})) = return objectId
 castObjectId directObject = expected "reference" directObject