Extract EXIF orientation metadata from images

src/Text/Pandoc/ImageSize.hs

@@ -14,13 +14,17 @@ Functions for determining the size of a PNG, JPEG, or GIF image.
 -}
 module Text.Pandoc.ImageSize ( ImageType(..)
                              , ImageSize(..)
+                             , ImageTransform(..)
                              , imageType
                              , imageSize
+                             , imageTransform
                              , sizeInPixels
                              , sizeInPoints
                              , desiredSizeInPoints
                              , Dimension(..)
                              , Direction(..)
+                             , Flip(..)
+                             , Rotate(..)
                              , dimension
                              , lengthToDim
                              , scaleDimension
@@ -52,6 +56,7 @@ import qualified Data.Text.Encoding as TE
 import Control.Applicative
 import qualified Data.Attoparsec.ByteString.Char8 as A
 import qualified Codec.Picture.Metadata as Metadata
+import Codec.Picture.Metadata.Exif (ExifTag(TagOrientation), ExifData(..))
 import Codec.Picture (decodeImageWithMetadata)
 
 -- quick and dirty functions to get image sizes
@@ -80,6 +85,19 @@ instance Show Dimension where
   show (Percent a)    = show a              ++ "%"
   show (Em a)         = T.unpack (showFl a) ++ "em"
 
+data Flip = NoFlip | FlipH | FlipV deriving Show
+
+data Rotate = R0 | R90 | R180 | R270 deriving Show
+
+data ImageTransform = ImageTransform
+  { tFlip :: Flip,
+    tRotate :: Rotate
+  }
+  deriving (Show)
+
+instance Default ImageTransform where
+  def = ImageTransform NoFlip R0
+
 data ImageSize = ImageSize{
                      pxX   :: Integer
                    , pxY   :: Integer
@@ -376,3 +394,25 @@ emfSize img =
     case parseheader . BL.fromStrict $ img of
       Left _ -> Nothing
       Right (_, _, size) -> Just size
+
+imageTransform :: ByteString -> Either T.Text ImageTransform
+imageTransform img = do
+  case decodeImageWithMetadata img of
+    Left e -> Left (T.pack e)
+    Right (_, meta) -> do
+      mbExif <- maybe (Right ExifNone)
+                Right $ Metadata.lookup (Metadata.Exif TagOrientation) meta
+      Right (exifToTransform (word mbExif))
+  where
+    word ExifNone = 1
+    word (ExifShort w) = w
+    word _ = 1
+    exifToTransform 1 = def
+    exifToTransform 2 = def{tFlip = FlipH}
+    exifToTransform 3 = def{tRotate = R180}
+    exifToTransform 4 = def{tFlip = FlipV}
+    exifToTransform 5 = def{tFlip = FlipH, tRotate = R270}
+    exifToTransform 6 = def{tRotate = R90}
+    exifToTransform 7 = def{tFlip = FlipH, tRotate = R90}
+    exifToTransform 8 = def{tRotate = R270}
+    exifToTransform _ = def