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{- git SHA stuff
-
- Copyright 2011 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Git.Sha where
import Common
import Git.Types
{- Runs an action that causes a git subcommand to emit a Sha, and strips
- any trailing newline, returning the sha. -}
getSha :: String -> IO String -> IO Sha
getSha subcommand a = maybe bad return =<< extractSha <$> a
where
bad = error $ "failed to read sha from git " ++ subcommand
{- Extracts the Sha from a string. There can be a trailing newline after
- it, but nothing else. -}
extractSha :: String -> Maybe Sha
extractSha s
| len == shaSize = val s
| len == shaSize + 1 && length s' == shaSize = val s'
| otherwise = Nothing
where
len = length s
s' = firstLine s
val v
| all (`elem` "1234567890ABCDEFabcdef") v = Just $ Ref v
| otherwise = Nothing
{- Size of a git sha. -}
shaSize :: Int
shaSize = 40
nullSha :: Ref
nullSha = Ref $ replicate shaSize '0'
{- Git's magic empty tree. -}
emptyTree :: Ref
emptyTree = Ref "4b825dc642cb6eb9a060e54bf8d69288fbee4904"
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