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|
{- git-annex single-value log
-
- This is used to store a value in a way that can be union merged.
-
- A line of the log will look like: "timestamp value"
-
- The line with the newest timestamp wins.
-
- Copyright 2014 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Logs.SingleValue where
import Common.Annex
import qualified Annex.Branch
import qualified Data.Set as S
import Data.Time.Clock.POSIX
import Data.Time
import System.Locale
class SingleValueSerializable v where
serialize :: v -> String
deserialize :: String -> Maybe v
data LogEntry v = LogEntry
{ changed :: POSIXTime
, value :: v
} deriving (Eq, Show, Ord)
type Log v = S.Set (LogEntry v)
showLog :: (SingleValueSerializable v) => Log v -> String
showLog = unlines . map showline . S.toList
where
showline (LogEntry t v) = unwords [show t, serialize v]
parseLog :: (Ord v, SingleValueSerializable v) => String -> Log v
parseLog = S.fromList . mapMaybe parse . lines
where
parse line = do
let (ts, s) = splitword line
date <- utcTimeToPOSIXSeconds <$> parseTime defaultTimeLocale "%s%Qs" ts
v <- deserialize s
Just (LogEntry date v)
splitword = separate (== ' ')
newestValue :: Log v -> Maybe v
newestValue s
| S.null s = Nothing
| otherwise = Just (value $ S.findMax s)
readLog :: (Ord v, SingleValueSerializable v) => FilePath -> Annex (Log v)
readLog = parseLog <$$> Annex.Branch.get
getLog :: (Ord v, SingleValueSerializable v) => FilePath -> Annex (Maybe v)
getLog = newestValue <$$> readLog
setLog :: (SingleValueSerializable v) => FilePath -> v -> Annex ()
setLog f v = do
now <- liftIO getPOSIXTime
let ent = LogEntry now v
Annex.Branch.change f $ \_old -> showLog (S.singleton ent)
|
