automatically derive an annex-uuid from a gcrypt-uuids

Git/GCrypt.hs

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+{- git-remote-gcrypt support
+ -
+ - https://github.com/blake2-ppc/git-remote-gcrypt
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Git.GCrypt where
+
+import Common
+import Git.Types
+import Git.Construct
+import Git.Config
+
+urlPrefix :: String
+urlPrefix = "gcrypt::"
+
+isEncrypted :: Repo -> Bool
+isEncrypted Repo { location = Url url } = urlPrefix `isPrefixOf` show url
+isEncrypted _ = False
+
+{- The first Repo is the git repository that has the second Repo
+ - as one of its remotes.
+ -
+ - When the remote Repo uses gcrypt, returns the actual underlying
+ - git repository that gcrypt is using to store its data. 
+ -
+ - Throws an exception if an url is invalid or the repo does not use
+ - gcrypt.
+ -}
+encryptedRepo :: Repo -> Repo -> IO Repo
+encryptedRepo baserepo = go
+  where
+  	go Repo { location = Url url }
+		| urlPrefix `isPrefixOf` u =
+			fromRemoteLocation (drop plen u) baserepo
+		| otherwise = notencrypted
+	  where
+  		u = show url
+		plen = length urlPrefix
+	go _ = notencrypted
+	notencrypted = error "not a gcrypt encrypted repository"
+
+{- gcrypt gives each encrypted repository a uique gcrypt-id,
+ - which is stored in the repository (in encrypted form)
+ - and cached in a per-remote gcrypt-id configuration setting. -}
+remoteRepoId :: Repo -> Repo -> Maybe String
+remoteRepoId baserepo remote = do
+	name <- remoteName remote
+	let key = "remote." ++ name ++ ".gcrypt-id"
+	getMaybe key baserepo