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{- git-annex vector clocks
-
- We don't have a way yet to keep true distributed vector clocks.
- The next best thing is a timestamp.
-
- Copyright 2017 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Annex.VectorClock where
import Data.Time.Clock.POSIX
import Control.Applicative
import Prelude
import Utility.Env
import Logs.TimeStamp
import Utility.QuickCheck
-- | Some very old logs did not have any time stamp at all;
-- Unknown is used for those.
data VectorClock = Unknown | VectorClock POSIXTime
deriving (Eq, Ord)
-- Unknown is oldest.
prop_VectorClock_sane :: Bool
prop_VectorClock_sane = Unknown < VectorClock 1
instance Arbitrary VectorClock where
arbitrary = VectorClock <$> arbitrary
currentVectorClock :: IO VectorClock
currentVectorClock = go =<< getEnv "GIT_ANNEX_VECTOR_CLOCK"
where
go Nothing = VectorClock <$> getPOSIXTime
go (Just s) = case parsePOSIXTime s of
Just t -> return (VectorClock t)
Nothing -> VectorClock <$> getPOSIXTime
formatVectorClock :: VectorClock -> String
formatVectorClock Unknown = "0"
formatVectorClock (VectorClock t) = show t
parseVectorClock :: String -> Maybe VectorClock
parseVectorClock t = VectorClock <$> parsePOSIXTime t
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