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+{- git-annex presence log, pure operations
+ -
+ - Copyright 2010-2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Logs.Presence.Pure where
+
+import Data.Time.Clock.POSIX
+import Data.Time
+import System.Locale
+import qualified Data.Map as M
+
+import Common.Annex
+import Utility.QuickCheck
+
+data LogLine = LogLine {
+	date :: POSIXTime,
+	status :: LogStatus,
+	info :: String
+} deriving (Eq, Show)
+
+data LogStatus = InfoPresent | InfoMissing
+	deriving (Eq, Show, Bounded, Enum)
+
+{- Parses a log file. Unparseable lines are ignored. -}
+parseLog :: String -> [LogLine]
+parseLog = mapMaybe parseline . lines
+  where
+	parseline l = LogLine
+		<$> (utcTimeToPOSIXSeconds <$> parseTime defaultTimeLocale "%s%Qs" d)
+		<*> parsestatus s
+		<*> pure rest
+	  where
+		(d, pastd) = separate (== ' ') l
+		(s, rest) = separate (== ' ') pastd
+	parsestatus "1" = Just InfoPresent
+	parsestatus "0" = Just InfoMissing
+	parsestatus _ = Nothing
+
+{- Generates a log file. -}
+showLog :: [LogLine] -> String
+showLog = unlines . map genline
+  where
+	genline (LogLine d s i) = unwords [show d, genstatus s, i]
+	genstatus InfoPresent = "1"
+	genstatus InfoMissing = "0"
+
+{- Given a log, returns only the info that is are still in effect. -}
+getLog :: String -> [String]
+getLog = map info . filterPresent . parseLog
+
+{- Returns the info from LogLines that are in effect. -}
+filterPresent :: [LogLine] -> [LogLine]
+filterPresent = filter (\l -> InfoPresent == status l) . compactLog
+
+{- Compacts a set of logs, returning a subset that contains the current
+ - status. -}
+compactLog :: [LogLine] -> [LogLine]
+compactLog = M.elems . foldr mapLog M.empty
+
+type LogMap = M.Map String LogLine
+
+{- Inserts a log into a map of logs, if the log has better (ie, newer)
+ - information than the other logs in the map -}
+mapLog :: LogLine -> LogMap -> LogMap
+mapLog l m
+	| better = M.insert i l m
+	| otherwise = m
+  where
+	better = maybe True newer $ M.lookup i m
+	newer l' = date l' <= date l
+	i = info l
+
+instance Arbitrary LogLine where
+	arbitrary = LogLine
+		<$> arbitrary
+		<*> elements [minBound..maxBound]
+		<*> arbitrary `suchThat` ('\n' `notElem`)
+
+prop_parse_show_log :: [LogLine] -> Bool
+prop_parse_show_log l = parseLog (showLog l) == l
+