{- git-annex presence log
 -
 - This is used to store presence information in the git-annex branch in
 - a way that can be union merged.
 -
 - A line of the log will look like: "date N INFO"
 - Where N=1 when the INFO is present, and 0 otherwise.
 - 
 - Copyright 2010-2011 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Logs.Presence (
	LogStatus(..),
	LogLine,
	addLog,
	readLog,
	getLog,
	parseLog,
	showLog,
	logNow,
	compactLog,
	currentLog,
) where

import Data.Time.Clock.POSIX
import Data.Time
import System.Locale
import qualified Data.Map as M

import Common.Annex
import qualified Annex.Branch

data LogLine = LogLine {
	date :: POSIXTime,
	status :: LogStatus,
	info :: String
} deriving (Eq)

data LogStatus = InfoPresent | InfoMissing
	deriving (Eq)

addLog :: FilePath -> LogLine -> Annex ()
addLog file line = Annex.Branch.change file $ \s -> 
	showLog $ compactLog (line : parseLog s)

{- Reads a log file.
 - Note that the LogLines returned may be in any order. -}
readLog :: FilePath -> Annex [LogLine]
readLog file = parseLog <$> Annex.Branch.get file

{- Parses a log file. Unparseable lines are ignored. -}
parseLog :: String -> [LogLine]
parseLog = mapMaybe (parseline . words) . lines
	where
		parseline (a:b:c:_) = do
			d <- parseTime defaultTimeLocale "%s%Qs" a
			s <- parsestatus b
			Just $ LogLine (utcTimeToPOSIXSeconds d) s c
		parseline _ = Nothing
		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"

{- Generates a new LogLine with the current date. -}
logNow :: LogStatus -> String -> Annex LogLine
logNow s i = do
	now <- liftIO getPOSIXTime
	return $ LogLine now s i

{- Reads a log and returns only the info that is still in effect. -}
currentLog :: FilePath -> Annex [String]
currentLog file = map info . filterPresent <$> readLog file

{- 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