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