Add to example programs to show how the lib can be used

Hufflepdf.cabal

@@ -32,3 +32,21 @@ library
   hs-source-dirs:      src
   ghc-options:         -Wall
   default-language:    Haskell2010
+
+executable             equivalent
+  main-is:             examples/equivalent.hs
+  build-depends:       base
+                     , bytestring
+                     , Hufflepdf
+  ghc-options:         -Wall
+  default-language:    Haskell2010
+
+executable             getObj
+  main-is:             examples/getObj.hs
+  build-depends:       base
+                     , bytestring
+                     , containers
+                     , Hufflepdf
+                     , zlib
+  ghc-options:         -Wall
+  default-language:    Haskell2010

examples/equivalent.hs

@@ -0,0 +1,13 @@
+import qualified Data.ByteString.Char8 as BS (readFile)
+import qualified Data.ByteString.Lazy.Char8 as Lazy (writeFile)
+import PDF (parseDocument, render)
+import System.Environment (getArgs)
+import System.IO (hPutStrLn, stderr)
+
+main :: IO ()
+main = do
+  [inputFile, outputFile] <- getArgs
+  result <- parseDocument <$> BS.readFile inputFile
+  case result of
+    Left parseError -> hPutStrLn stderr parseError
+    Right doc -> Lazy.writeFile outputFile $ render doc

examples/getObj.hs

@@ -0,0 +1,37 @@
+{-# LANGUAGE NamedFieldPuns #-}
+
+import Codec.Compression.Zlib (decompress)
+import Data.ByteString.Lazy.Char8 (ByteString)
+import qualified Data.ByteString.Char8 as BS (readFile)
+import qualified Data.ByteString.Lazy.Char8 as Lazy (concat, fromStrict, putStr, toStrict)
+import Data.Map ((!))
+import qualified Data.Map as Map (lookup)
+import PDF (Document(..), parseDocument)
+import qualified PDF.EOL as EOL (Style)
+import PDF.Object (Content(..), DirectObject(..), Object(..), Name(..))
+import PDF.Output (ObjectId(..))
+import qualified PDF.Output as Output (render)
+import System.Environment (getArgs)
+import System.IO (hPutStrLn, stderr)
+
+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 -> ByteString
+extractObject objectId (Document {eolStyle, updates}) =
+  Lazy.concat $ display eolStyle . (!objectId) . objects  <$> updates
+
+main :: IO ()
+main = do
+  [inputFile, objectId] <- getArgs
+  result <- parseDocument <$> BS.readFile inputFile
+  case result of
+    Left parseError -> hPutStrLn stderr $ show parseError
+    Right doc -> Lazy.putStr $ extractObject (ObjectId (read objectId)) doc