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{- git-annex Map log
-
- This is used to store a Map, in a way that can be union merged.
-
- A line of the log will look like: "timestamp field value"
-
- The field names cannot contain whitespace.
-
- Copyright 2014, 2019 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Logs.MapLog (
module Logs.MapLog,
VectorClock,
currentVectorClock,
) where
import Common
import Annex.VectorClock
import Logs.Line
import qualified Data.ByteString.Lazy as L
import qualified Data.Map.Strict as M
import qualified Data.Attoparsec.ByteString.Lazy as A
import qualified Data.Attoparsec.ByteString.Char8 as A8
import Data.ByteString.Builder
data LogEntry v = LogEntry
{ changed :: VectorClock
, value :: v
} deriving (Eq, Show)
type MapLog f v = M.Map f (LogEntry v)
buildMapLog :: (f -> Builder) -> (v -> Builder) -> MapLog f v -> Builder
buildMapLog fieldbuilder valuebuilder = mconcat . map genline . M.toList
where
genline (f, LogEntry c v) =
buildVectorClock c <> sp
<> fieldbuilder f <> sp
<> valuebuilder v <> nl
sp = charUtf8 ' '
nl = charUtf8 '\n'
parseMapLog :: Ord f => A.Parser f -> A.Parser v -> L.ByteString -> MapLog f v
parseMapLog fieldparser valueparser = fromMaybe M.empty . A.maybeResult
. A.parse (mapLogParser fieldparser valueparser)
mapLogParser :: Ord f => A.Parser f -> A.Parser v -> A.Parser (MapLog f v)
mapLogParser fieldparser valueparser = M.fromListWith best <$> parseLogLines go
where
go = do
c <- vectorClockParser
_ <- A8.char ' '
w <- A8.takeTill (== ' ')
f <- either fail return $
A.parseOnly (fieldparser <* A.endOfInput) w
_ <- A8.char ' '
v <- valueparser
A.endOfInput
return (f, LogEntry c v)
changeMapLog :: Ord f => VectorClock -> f -> v -> MapLog f v -> MapLog f v
changeMapLog c f v = M.insert f $ LogEntry c v
{- Only add an LogEntry if it's newer (or at least as new as) than any
- existing LogEntry for a field. -}
addMapLog :: Ord f => f -> LogEntry v -> MapLog f v -> MapLog f v
addMapLog = M.insertWith best
{- Converts a MapLog into a simple Map without the timestamp information.
- This is a one-way trip, but useful for code that never needs to change
- the log. -}
simpleMap :: MapLog f v -> M.Map f v
simpleMap = M.map value
best :: LogEntry v -> LogEntry v -> LogEntry v
best new old
| changed old > changed new = old
| otherwise = new
prop_addMapLog_sane :: Bool
prop_addMapLog_sane = newWins && newestWins
where
newWins = addMapLog ("foo") (LogEntry (VectorClock 1) "new") l == l2
newestWins = addMapLog ("foo") (LogEntry (VectorClock 1) "newest") l2 /= l2
l = M.fromList [("foo", LogEntry (VectorClock 0) "old")]
l2 = M.fromList [("foo", LogEntry (VectorClock 1) "new")]
|
