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.

4 files changed, 50 insertions, 43 deletions

diff --git a/src/Text/Pandoc/Class/IO.hs b/src/Text/Pandoc/Class/IO.hs
index bb4e2b732..f12c0a938 100644
--- a/src/Text/Pandoc/Class/IO.hs
+++ b/src/Text/Pandoc/Class/IO.hs
@@ -62,7 +62,7 @@ import Text.Pandoc.Definition (Pandoc, Inline (Image))
 import Text.Pandoc.Error (PandocError (..))
 import Text.Pandoc.Logging (LogMessage (..), messageVerbosity, showLogMessage)
 import Text.Pandoc.MIME (MimeType)
-import Text.Pandoc.MediaBag (MediaBag, lookupMedia, mediaDirectory)
+import Text.Pandoc.MediaBag (MediaBag, MediaItem(..), lookupMedia, mediaDirectory)
 import Text.Pandoc.Walk (walk)
 import qualified Control.Exception as E
 import qualified Data.ByteString as B
@@ -213,14 +213,13 @@ writeMedia :: (PandocMonad m, MonadIO m)
 writeMedia dir mediabag subpath = do
   -- we join and split to convert a/b/c to a\b\c on Windows;
   -- in zip containers all paths use /
-  let fullpath = dir </> unEscapeString (normalise subpath)
   let mbcontents = lookupMedia subpath mediabag
   case mbcontents of
        Nothing -> throwError $ PandocResourceNotFound $ pack subpath
-       Just (_, bs) -> do
-         report $ Extracting $ pack fullpath
+       Just item -> do
+         let fullpath = dir </> mediaPath item
          liftIOError (createDirectoryIfMissing True) (takeDirectory fullpath)
-         logIOError $ BL.writeFile fullpath bs
+         logIOError $ BL.writeFile fullpath $ mediaContents item
 
 -- | If the given Inline element is an image with a @src@ path equal to
 -- one in the list of @paths@, then prepends @dir@ to the image source;
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
diff --git a/src/Text/Pandoc/Lua/Module/MediaBag.hs b/src/Text/Pandoc/Lua/Module/MediaBag.hs
index 78b699176..3eed50fca 100644
--- a/src/Text/Pandoc/Lua/Module/MediaBag.hs
+++ b/src/Text/Pandoc/Lua/Module/MediaBag.hs
@@ -73,9 +73,9 @@ lookup fp = do
   res <- MB.lookupMedia fp <$> getMediaBag
   liftPandocLua $ case res of
     Nothing -> 1 <$ Lua.pushnil
-    Just (mimeType, contents) -> do
-      Lua.push mimeType
-      Lua.push contents
+    Just item -> do
+      Lua.push $ MB.mediaMimeType item
+      Lua.push $ MB.mediaContents item
       return 2
 
 list :: PandocLua NumResults
diff --git a/src/Text/Pandoc/MediaBag.hs b/src/Text/Pandoc/MediaBag.hs
index 4a9b4efa1..a65f315fc 100644
--- a/src/Text/Pandoc/MediaBag.hs
+++ b/src/Text/Pandoc/MediaBag.hs
@@ -15,6 +15,7 @@ Definition of a MediaBag object to hold binary resources, and an
 interface for interacting with it.
 -}
 module Text.Pandoc.MediaBag (
+                     MediaItem(..),
                      MediaBag,
                      deleteMedia,
                      lookupMedia,
@@ -28,15 +29,23 @@ import qualified Data.Map as M
 import Data.Maybe (fromMaybe)
 import Data.Typeable (Typeable)
 import System.FilePath
-import Text.Pandoc.MIME (MimeType, getMimeTypeDef)
+import Text.Pandoc.MIME (MimeType, getMimeTypeDef, extensionFromMimeType)
 import Data.Text (Text)
 import qualified Data.Text as T
+import Data.Digest.Pure.SHA (sha1, showDigest)
+
+data MediaItem =
+  MediaItem
+  { mediaMimeType :: MimeType
+  , mediaPath :: FilePath
+  , mediaContents :: BL.ByteString
+  } deriving (Eq, Ord, Show, Data, Typeable)
 
 -- | A container for a collection of binary resources, with names and
 -- mime types.  Note that a 'MediaBag' is a Monoid, so 'mempty'
 -- can be used for an empty 'MediaBag', and '<>' can be used to append
 -- two 'MediaBag's.
-newtype MediaBag = MediaBag (M.Map Text (MimeType, BL.ByteString))
+newtype MediaBag = MediaBag (M.Map Text MediaItem)
         deriving (Semigroup, Monoid, Data, Typeable)
 
 instance Show MediaBag where
@@ -62,26 +71,34 @@ insertMedia :: FilePath       -- ^ relative path and canonical name of resource
             -> MediaBag
             -> MediaBag
 insertMedia fp mbMime contents (MediaBag mediamap) =
-  MediaBag (M.insert (canonicalize fp) (mime, contents) mediamap)
-  where mime = fromMaybe fallback mbMime
+  MediaBag (M.insert (canonicalize fp) mediaItem mediamap)
+  where mediaItem = MediaItem{ mediaPath = showDigest (sha1 contents) <>
+                                 "." <> ext
+                             , mediaContents = contents
+                             , mediaMimeType = mt }
         fallback = case takeExtension fp of
                         ".gz" -> getMimeTypeDef $ dropExtension fp
                         _     -> getMimeTypeDef fp
+        mt = fromMaybe fallback mbMime
+        ext = maybe (takeExtension fp) T.unpack $ extensionFromMimeType mt
+
 
 -- | Lookup a media item in a 'MediaBag', returning mime type and contents.
 lookupMedia :: FilePath
             -> MediaBag
-            -> Maybe (MimeType, BL.ByteString)
+            -> Maybe MediaItem
 lookupMedia fp (MediaBag mediamap) = M.lookup (canonicalize fp) mediamap
 
 -- | Get a list of the file paths stored in a 'MediaBag', with
 -- their corresponding mime types and the lengths in bytes of the contents.
 mediaDirectory :: MediaBag -> [(FilePath, MimeType, Int)]
 mediaDirectory (MediaBag mediamap) =
-  M.foldrWithKey (\fp (mime,contents) ->
-      ((T.unpack fp, mime, fromIntegral (BL.length contents)):)) [] mediamap
+  M.foldrWithKey (\fp item ->
+      ((T.unpack fp, mediaMimeType item,
+        fromIntegral (BL.length (mediaContents item))):)) [] mediamap
 
 mediaItems :: MediaBag -> [(FilePath, MimeType, BL.ByteString)]
 mediaItems (MediaBag mediamap) =
-  M.foldrWithKey (\fp (mime,contents) ->
-      ((T.unpack fp, mime, contents):)) [] mediamap
+  M.foldrWithKey (\fp item ->
+      ((T.unpack fp, mediaMimeType item, mediaContents item):))
+     [] mediamap