git-annex/Annex/GitShaKey.hs
2025-03-03 11:09:28 -04:00

41 lines
1.1 KiB
Haskell

{- 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