Simplify navigations by centering everything on Objects to avoid needing to many conversion tools between DirectObject / Object / Dictionary

examples/getObj.hs

@@ -8,7 +8,7 @@ import qualified Data.ByteString.Lazy.Char8 as Lazy (putStrLn)
 import PDF (Document(..), parseDocument)
 import PDF.Object (Content(..), Object(..))
 import PDF.Object.Navigation (
-    Error(..), (//), castObject, objectById, openStream, origin
+    Error(..), (//), objectById, openStream, origin
   )
 import PDF.Output (ObjectId(..), Output)
 import qualified PDF.Output as Output (render)
@@ -34,7 +34,7 @@ parse [inputFile, key] =
   return (inputFile, clear . maybe (byPath key) byId $ readMaybe key)
   where
     byId = objectById . ObjectId
-    byPath path = (origin >>= (// (explode path)) >>= castObject)
+    byPath path = origin // (explode path)
     explode "" = []
     explode path =
       case break (== '.') path of

src/PDF/Object/Navigation.hs

@@ -4,12 +4,11 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 module PDF.Object.Navigation (
       Error(..)
+    , (./)
     , (//)
-    , castObject
-    , dictionaryById
+    , (>./)
+    , (>//)
     , getDictionary
-    , getField
-    , follow
     , objectById
     , openStream
     , origin
@@ -39,21 +38,12 @@ newtype Error a = Error {
 instance MonadFail Error where
   fail = Error . Left
 
-castDictionary :: MonadFail m => Object -> m Dictionary
-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
-
-dictionaryById :: PDFContent m => ObjectId -> m Dictionary
-dictionaryById objectId = objectById objectId >>= castDictionary
+getDictionary :: PDFContent m => Object -> m Dictionary
+getDictionary (Direct (Dictionary aDict)) = return aDict
+getDictionary (Direct (Reference (IndirectObjCoordinates {objectId}))) =
+  objectById objectId >>= getDictionary
+getDictionary (Stream {header}) = return header
+getDictionary obj = expected "dictionary : " obj
 
 expected :: (MonadFail m, Show a) => String -> a -> m b
 expected name = fail . printf "Not a %s: %s" name . show
@@ -65,28 +55,30 @@ getField key aDictionary =
     errorMessage =
       printf "Key %s not found in dictionary %s" key (show aDictionary)
 
-follow :: PDFContent m => DirectObject -> m Object
-follow directObject = castObjectId directObject >>= objectById
-
 objectById :: PDFContent m => ObjectId -> m Object
 objectById objectId = do
   content <- ask
   return (objects content ! objectId)
 
-getDictionary :: PDFContent m => DirectObject -> m Dictionary
-getDictionary (Dictionary aDictionary) = return aDictionary
-getDictionary (Reference (IndirectObjCoordinates {objectId})) =
-  objectById objectId >>= castDictionary
-getDictionary aDirectObject =
-  expected "resource (dictionary or reference)" aDirectObject
+(./) :: PDFContent m => m Object -> String -> m Object
+(./) object key = (object >>= getDictionary >>= getField key >>= castObject)
+  where
+    castObject (Reference (IndirectObjCoordinates {objectId})) =
+      objectById objectId
+    castObject directObject = return $ Direct directObject
 
-(//) :: PDFContent m => Dictionary -> [String] -> m DirectObject
-(//) aDict [] = return $ Dictionary aDict
-(//) aDict [key] = getField key aDict
-(//) aDict (key:keys) = getField key aDict >>= getDictionary >>= (// keys)
+(//) :: PDFContent m => m Object -> [String] -> m Object
+(//) object [] = object
+(//) object (key:keys) = object ./ key // keys
 
-origin :: PDFContent m => m Dictionary
-origin = trailer . docStructure <$> ask
+(>./) :: PDFContent m => Object -> String -> m Object
+(>./) object = (return object ./)
+
+(>//) :: PDFContent m => Object -> [String] -> m Object
+(>//) object = (return object //)
+
+origin :: PDFContent m => m Object
+origin = Direct . Dictionary . trailer . docStructure <$> ask
 
 openStream :: MonadFail m => Object -> m ByteString
 openStream (Stream {header, streamContent}) = return $

src/PDF/Pages.hs

@@ -20,10 +20,11 @@ import PDF.Encoding (encoding)
 import PDF.Font (Font, FontSet)
 import PDF.Object (
       Content(..), Dictionary, DirectObject(..), IndirectObjCoordinates(..)
-    , Name(..)
+    , Name(..), Object(..)
   ,)
 import PDF.Object.Navigation (
-    Error(..), (//), dictionaryById, getDictionary, getField, follow, openStream, origin
+      Error(..), (//), (>./), (>//), getDictionary, objectById, openStream
+    , origin
   )
 import PDF.Output (ObjectId(..))
 import Prelude hiding (fail)
@@ -36,9 +37,9 @@ data Page = Page {
     , source :: ObjectId
   }
 
-getFontDictionary :: Dictionary -> T Dictionary
-getFontDictionary pageDict =
-    ((pageDict // ["Resources", "Font"]) >>= getDictionary)
+getFontDictionary :: Object -> T Dictionary
+getFontDictionary pageObj =
+    (pageObj >// ["Resources", "Font"] >>= getDictionary)
   <|> return Map.empty
 
 cache :: (ObjectId -> T Font) -> ObjectId -> T Font
@@ -51,20 +52,17 @@ cache loader objectId =
       return value
 
 loadFont :: ObjectId -> T Font
-loadFont objectId = dictionaryById objectId >>= tryMappings
+loadFont objectId = objectById objectId >>= tryMappings
   where
-    tryMappings dictionary =
-        loadCMap dictionary
-      <|> (getField "Encoding" dictionary >>= loadEncoding)
-      <|> (fail $ unknownFormat (show objectId) (show dictionary))
+    tryMappings object =
+        (object >./ "ToUnicode" >>= openStream >>= cMap)
+      <|> (object >./ "Encoding" >>= loadEncoding)
+      <|> (fail $ unknownFormat (show objectId) (show object))
     unknownFormat = printf "Unknown font format for object #%s : %s"
-    loadCMap :: Dictionary -> T Font
-    loadCMap dictionary =
-      getField "ToUnicode" dictionary >>= follow >>= openStream >>= cMap
-    loadEncoding :: DirectObject -> T Font
-    loadEncoding (NameObject (Name name)) = encoding name
-    loadEncoding directObject =
-      fail $ printf "Encoding must be a name, not that : %s" $ show directObject
+    loadEncoding :: Object -> T Font
+    loadEncoding (Direct (NameObject (Name name))) = encoding name
+    loadEncoding object =
+      fail $ printf "Encoding must be a name, not that : %s" $ show object
 
 loadFonts :: Dictionary -> T FontSet
 loadFonts = foldM addFont Map.empty . Map.toList
@@ -74,13 +72,13 @@ loadFonts = foldM addFont Map.empty . Map.toList
       flip (Map.insert name) output <$> cache loadFont objectId
     addFont output _ = return output
 
-several :: DirectObject -> [DirectObject]
-several (Array l) =  l
-several directObject = [directObject]
+several :: Object -> [Object]
+several (Direct (Array l)) =  Direct <$> l
+several object = [object]
 
 pagesList :: T [ObjectId]
 pagesList = do
-  pages <- (origin :: T Dictionary) >>= (// ["Root", "Pages"]) >>= getDictionary
+  pages <- origin // ["Root", "Pages"] >>= getDictionary
   case Map.lookup (Name "Kids") pages of
     Just (Array kids) -> return $ getReferences kids
     _ -> return []
@@ -92,22 +90,21 @@ getReferences objects = do
     Reference (IndirectObjCoordinates {objectId}) -> [objectId]
     _ -> []
 
-extractText :: Dictionary -> T [Text]
-extractText pageDict = do
-  fonts <- loadFonts =<< getFontDictionary pageDict
-  objects <- several <$> getField "Contents" pageDict
+extractText :: Object -> T [Text]
+extractText pageObj = do
+  fonts <- loadFonts =<< getFontDictionary pageObj
+  objects <- several <$> pageObj >./ "Contents"
   concat <$> mapM (loadContent fonts) objects
   where
-    loadContent :: FontSet -> DirectObject -> T [Text]
-    loadContent fonts directObject =
-        follow directObject
-      >>= openStream
+    loadContent :: FontSet -> Object -> T [Text]
+    loadContent fonts object =
+        openStream object
       >>= (either fail return . Content.parse)
       >>= renderText fonts
 
 loadPage :: ObjectId -> T Page
 loadPage source = do
-  contents <- extractText =<< dictionaryById source
+  contents <- extractText =<< objectById source
   return $ Page {contents, source}
 
 getAll :: Content -> Either String (Map Int Page)