copied from git-annex

1 files changed, 39 insertions, 0 deletions

diff --git a/Git/Sha.hs b/Git/Sha.hs
new file mode 100644
index 0000000..ee1b6d6
--- /dev/null
+++ b/Git/Sha.hs
@@ -0,0 +1,39 @@
+{- 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'