Plan for parsing Darcs patch for patch view

src/Vervis/Darcs.hs

@@ -18,6 +18,7 @@ module Vervis.Darcs
     , readWikiView
     , readChangesView
     , lastChange
+    , readPatch
     )
 where
 
@@ -55,6 +56,7 @@ import Data.Text.UTF8.Local (decodeStrict)
 import Data.Time.Clock.Local ()
 import Vervis.Changes
 import Vervis.Foundation (Widget)
+import Vervis.Patch
 import Vervis.Readme
 import Vervis.SourceTree
 import Vervis.Wiki (WikiView (..))
@@ -218,3 +220,41 @@ lastChange path now = fmap maybeRight $ runExceptT $ do
             intervalToEventTime $
             FriendlyConvert $
             now `diffUTCTime` piTime pi
+
+-- TODO
+readPatch :: FilePath -> Text -> IO (Maybe Patch)
+readPatch path hash = error "Not implemented"
+    -- I'm not sure what's the fastest way to find a patch file given its info
+    -- hash, maybe Darcs keeps some cache or something. But assuming there are
+    -- no tricks like that, here's an idea how to grab the patch:
+    --
+    -- (1) Start going over the whole inventory, whose order is from latest to
+    --     oldest, looking for a patch with the given hash.
+    -- (2) Once found, determine the patch filename from its size and content
+    --     hash
+    -- (3) Run the patch parser on that file, through a zlib decompressor
+    --     though (check how I did that for the inventories parser)
+    --
+    -- TODO idea: Use hints to speed up finding the patch! In the repo history
+    -- log page, embed hints into the hyperlinks to the patches, and in the
+    -- patch page handler, use the hint to figure out the patch location.
+    -- Actually, since the inventory file contains patch content hashes, I can
+    -- use that as a hint and skip the whole step of looking for the patch!
+    --
+    -- TODO maybe start by finding the patch hash in patch_ids and use the
+    -- position as a hint to its location in the inventories
+    --
+    -- TODO maybe I can figure out from darcs source code how a given patch
+    -- hash is found? Just in case there's a faster way
+    --
+    -- TODO find out what's the index and patch_index files under _darcs and
+    -- maybe other files there, possibly there's a way to patch the info hash
+    -- with the content hash.
+    --
+    -- UPDATE: I read about index and patch_index, looks like they won't help.
+    -- But possibly the global cache system will? However interesting note:
+    -- Vervis on my laptop has a patch_index, but on the server it doesn't.
+    -- Probably because `darcs log` never runs on the server since I parse
+    -- patches manually. If I end up using the patch index for something, it
+    -- may be a good idea to trigger its generation, so that it's available
+    -- when people browser repo pages.

src/Vervis/Handler/Repo.hs

@@ -263,7 +263,7 @@ getRepoPatchR :: ShrIdent -> RpIdent -> Text -> Handler Html
 getRepoPatchR shr rp ref = do
     repository <- runDB $ selectRepo shr rp
     case repoVcs repository of
-        VCSDarcs -> error "Not implemented yet" -- getDarcsPatch shr rp ref
+        VCSDarcs -> getDarcsPatch shr rp ref
         VCSGit -> getGitPatch shr rp ref
 
 getRepoDevsR :: ShrIdent -> RpIdent -> Handler Html

src/Vervis/Handler/Repo/Darcs.hs

@@ -18,6 +18,7 @@ module Vervis.Handler.Repo.Darcs
     , getDarcsRepoHeadChanges
     , getDarcsRepoChanges
     , getDarcsDownloadR
+    , getDarcsPatch
     )
 where
 
@@ -106,3 +107,6 @@ getDarcsDownloadR shar repo dir = do
     if exists
         then sendFile typeOctet filePath
         else notFound
+
+getDarcsPatch :: ShrIdent -> RpIdent -> Text -> Handler Html
+getDarcsPatch shr rp ref = error "Not implemented"