MediaBag improvements.

In the current dev version, we will sometimes add
a version of an image with a hashed name, keeping
the original version with the original name, which
would leave to undesirable duplication.

This change separates the media's filename from the
media's canonical name (which is the path of the link
in the document itself).  Filenames are based on SHA1
hashes and assigned automatically.

In Text.Pandoc.MediaBag:

- Export MediaItem type [API change].
- Change MediaBag type to a map from Text to MediaItem [API change].
- `lookupMedia` now returns a `MediaItem` [API change].
- Change `insertMedia` so it sets the `mediaPath` to
  a filename based on the SHA1 hash of the contents.
  This will be used when contents are extracted.

In Text.Pandoc.Class.PandocMonad:

- Remove `fetchMediaResource` [API change].

Lua MediaBag module has been changed minimally. In the future
it would be better, probably, to give Lua access to the full
MediaItem type.

1 files changed, 17 insertions, 26 deletions

diff --git a/src/Text/Pandoc/Class/PandocMonad.hs b/src/Text/Pandoc/Class/PandocMonad.hs
index dd6499a73..ae6917e06 100644
--- a/src/Text/Pandoc/Class/PandocMonad.hs
+++ b/src/Text/Pandoc/Class/PandocMonad.hs
@@ -37,7 +37,6 @@ module Text.Pandoc.Class.PandocMonad
   , setUserDataDir
   , getUserDataDir
   , fetchItem
-  , fetchMediaResource
   , getInputFiles
   , setInputFiles
   , getOutputFile
@@ -57,8 +56,6 @@ module Text.Pandoc.Class.PandocMonad
 import Codec.Archive.Zip
 import Control.Monad.Except (MonadError (catchError, throwError),
                              MonadTrans, lift, when)
-import Data.Digest.Pure.SHA (sha1, showDigest)
-import Data.Maybe (fromMaybe)
 import Data.List (foldl')
 import Data.Time (UTCTime)
 import Data.Time.Clock.POSIX (POSIXTime, utcTimeToPOSIXSeconds,
@@ -67,7 +64,7 @@ import Data.Time.LocalTime (TimeZone, ZonedTime, utcToZonedTime)
 import Network.URI ( escapeURIString, nonStrictRelativeTo,
                      unEscapeString, parseURIReference, isAllowedInURI,
                      parseURI, URI(..) )
-import System.FilePath ((</>), (<.>), takeExtension, dropExtension,
+import System.FilePath ((</>), takeExtension, dropExtension,
                         isRelative, splitDirectories)
 import System.Random (StdGen)
 import Text.Collate.Lang (Lang(..), parseLang, renderLang)
@@ -75,8 +72,8 @@ import Text.Pandoc.Class.CommonState (CommonState (..))
 import Text.Pandoc.Definition
 import Text.Pandoc.Error
 import Text.Pandoc.Logging
-import Text.Pandoc.MIME (MimeType, getMimeType, extensionFromMimeType)
-import Text.Pandoc.MediaBag (MediaBag, lookupMedia)
+import Text.Pandoc.MIME (MimeType, getMimeType)
+import Text.Pandoc.MediaBag (MediaBag, lookupMedia, MediaItem(..))
 import Text.Pandoc.Shared (uriPathToPath, safeRead)
 import Text.Pandoc.Translations (Term(..), Translations, lookupTerm,
                                  readTranslations)
@@ -376,7 +373,8 @@ fetchItem :: PandocMonad m
 fetchItem s = do
   mediabag <- getMediaBag
   case lookupMedia (T.unpack s) mediabag of
-    Just (mime, bs) -> return (BL.toStrict bs, Just mime)
+    Just item -> return (BL.toStrict (mediaContents item),
+                         Just (mediaMimeType item))
     Nothing -> downloadOrRead s
 
 -- | Returns the content and, if available, the MIME type of a resource.
@@ -629,19 +627,6 @@ withPaths (p:ps) action fp =
   catchError (action (p </> fp))
              (\_ -> withPaths ps action fp)
 
--- | Fetch local or remote resource (like an image) and provide data suitable
--- for adding it to the MediaBag.
-fetchMediaResource :: PandocMonad m
-              => T.Text -> m (FilePath, Maybe MimeType, BL.ByteString)
-fetchMediaResource src = do
-  (bs, mt) <- fetchItem src
-  let ext = fromMaybe (T.pack $ takeExtension $ T.unpack src)
-                      (mt >>= extensionFromMimeType)
-  let bs' = BL.fromChunks [bs]
-  let basename = showDigest $ sha1 bs'
-  let fname = basename <.> T.unpack ext
-  return (fname, mt, bs')
-
 -- | Traverse tree, filling media bag for any images that
 -- aren't already in the media bag.
 fillMediaBag :: PandocMonad m => Pandoc -> m Pandoc
@@ -649,12 +634,18 @@ fillMediaBag d = walkM handleImage d
   where handleImage :: PandocMonad m => Inline -> m Inline
         handleImage (Image attr lab (src, tit)) = catchError
           (do mediabag <- getMediaBag
-              case lookupMedia (T.unpack src) mediabag of
-                Just (_, _) -> return $ Image attr lab (src, tit)
-                Nothing -> do
-                  (fname, mt, bs) <- fetchMediaResource src
-                  insertMedia fname mt bs
-                  return $ Image attr lab (T.pack fname, tit))
+              let fp = T.unpack src
+              src' <- T.pack <$> case lookupMedia fp mediabag of
+                        Just item -> return $ mediaPath item
+                        Nothing -> do
+                          (bs, mt) <- fetchItem src
+                          insertMedia fp mt (BL.fromStrict bs)
+                          mediabag' <- getMediaBag
+                          case lookupMedia fp mediabag' of
+                             Just item -> return $ mediaPath item
+                             Nothing -> throwError $ PandocSomeError $
+                               src <> " not successfully inserted into MediaBag"
+              return $ Image attr lab (src', tit))
           (\e ->
               case e of
                 PandocResourceNotFound _ -> do