factor out Annex.GitShaKey

Annex/GitShaKey.hs

@@ -0,0 +1,41 @@
+{- Encoding a git sha as a Key
+ -
+ - Copyright 2017-2025 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Annex.GitShaKey where
+
+import Types
+import Types.Key
+import qualified Git
+
+import Data.Maybe
+import qualified Data.ByteString.Short as S (fromShort, toShort)
+
+-- Encodes a git sha as a Key. This is used to represent a non-annexed
+-- file. For example, when storing a git sha on a special remote.
+--
+-- This is not the same as a SHA1 key, because the mapping needs to be
+-- bijective, also because git may not always use SHA1, and because git
+-- takes a SHA1 of the file size + content, while git-annex SHA1 keys
+-- only checksum the content.
+gitShaKey :: Git.Sha -> Key
+gitShaKey (Git.Ref s) = mkKey $ \kd -> kd
+	{ keyName = S.toShort s
+	, keyVariety = OtherKey "GIT"
+	}
+
+-- Reverse of gitShaKey
+keyGitSha :: Key -> Maybe Git.Sha
+keyGitSha k
+	| fromKey keyVariety k == OtherKey "GIT" =
+		Just (Git.Ref (S.fromShort (fromKey keyName k)))
+	| otherwise = Nothing
+
+-- Is a key storing a git sha, and not used for an annexed file?
+isGitShaKey :: Key -> Bool
+isGitShaKey = isJust . keyGitSha