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