half way complete cronner thread to run scheduled activities

Assistant/Threads/Cronner.hs

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+{- git-annex assistant sceduled jobs runner
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+{-# LANGUAGE DeriveDataTypeable #-}
+
+module Assistant.Threads.Cronner (
+	cronnerThread
+) where
+
+import Assistant.Common
+import Assistant.DaemonStatus
+import Utility.NotificationBroadcaster
+import Logs.Schedule
+import Annex.UUID
+import Types.ScheduledActivity
+
+import Control.Concurrent.Async
+import Data.Time.LocalTime
+import qualified Data.Map as M
+import qualified Data.Set as S
+import qualified Control.Exception as E
+import Data.Typeable
+
+data ActivityException = PleaseTerminate
+	deriving (Typeable, Show)
+
+instance E.Exception ActivityException
+
+{- Loads schedules for this repository, and fires off one thread for each 
+ - scheduled event. These threads sleep until the next time the event
+ - should run.
+ -
+ - In the meantime the main thread waits for any changes to the
+ - schedules. When there's a change, compare the old and new list of
+ - schedules to find deleted and added ones. Start new threads for added
+ - ones, and send the threads a PleaseTerminate exception for the deleted
+ - ones. -}
+cronnerThread :: NamedThread
+cronnerThread = namedThreadUnchecked "Cronner" $ do
+	dstatus <- getDaemonStatus
+	h <- liftIO $ newNotificationHandle False (scheduleLogNotifier dstatus)
+	go h M.empty
+  where
+	go h m = do
+		activities <- liftAnnex $ scheduleGet =<< getUUID
+
+		let addedactivities = activities `S.difference` M.keysSet m
+		let removedactivities = M.keysSet m `S.difference` activities
+
+		liftIO $ forM_ (mapMaybe (`M.lookup` m) $ S.toList removedactivities) $ 
+			flip cancelWith PleaseTerminate
+
+		lastruntimes <- liftAnnex getLastRunTimes
+		addedm <- M.fromList <$> startactivities (S.toList addedactivities) lastruntimes
+
+		liftIO $ waitNotification h
+
+		let m' = M.difference (M.union addedm m)
+			(M.filterWithKey (\k _ -> S.member k removedactivities) m)
+		go h m'
+  	startactivities as lastruntimes = forM as $ \activity -> do
+		runner <- asIO2 activityThread
+		a <- liftIO $ async $
+			runner activity (M.lookup activity lastruntimes)
+		return (activity, a)
+
+{- Calculate the next time the activity is scheduled to run, then
+ - sleep until that time, and run it. Then call setLastRunTime, and
+ - loop.
+ -
+ - At any point, a PleaseTerminate could be received. This should result in
+ - the thread and any processes it has run shutting down.
+ -}
+activityThread :: ScheduledActivity -> Maybe LocalTime -> Assistant ()
+activityThread activity lastrun = do
+	noop