{- git-annex assistant change tracking and committing
 -
 - Copyright 2012 Joey Hess <joey@kitenet.net>
 -}

module Assistant.Committer where

import Common.Annex
import Assistant.ThreadedMonad
import qualified Annex.Queue
import qualified Git.Command
import qualified Command.Add
import Utility.ThreadScheduler
import qualified Utility.Lsof as Lsof
import Types.Backend

import Control.Concurrent.STM
import Data.Time.Clock
import Data.Tuple.Utils
import qualified Data.Set as S

data ChangeType = PendingAddChange | LinkChange | RmChange | RmDirChange
	deriving (Show, Eq)

type ChangeChan = TChan Change

data Change = Change
	{ changeTime :: UTCTime
	, changeFile :: FilePath
	, changeType :: ChangeType
	}
	deriving (Show)

runChangeChan :: STM a -> IO a
runChangeChan = atomically

newChangeChan :: IO ChangeChan
newChangeChan = atomically newTChan

{- Handlers call this when they made a change that needs to get committed. -}
madeChange :: FilePath -> ChangeType -> Annex (Maybe Change)
madeChange f t = do
	-- Just in case the commit thread is not flushing the queue fast enough.
	when (t /= PendingAddChange) $
		Annex.Queue.flushWhenFull
	liftIO $ Just <$> (Change <$> getCurrentTime <*> pure f <*> pure t)

noChange :: Annex (Maybe Change)
noChange = return Nothing

{- Gets all unhandled changes.
 - Blocks until at least one change is made. -}
getChanges :: ChangeChan -> IO [Change]
getChanges chan = runChangeChan $ do
	c <- readTChan chan
	go [c]
	where
		go l = do
			v <- tryReadTChan chan
			case v of
				Nothing -> return l
				Just c -> go (c:l)

{- Puts unhandled changes back into the channel.
 - Note: Original order is not preserved. -}
refillChanges :: ChangeChan -> [Change] -> IO ()
refillChanges chan cs = runChangeChan $ mapM_ (writeTChan chan) cs

{- This thread makes git commits at appropriate times. -}
commitThread :: ThreadState -> ChangeChan -> IO ()
commitThread st changechan = runEvery (Seconds 1) $ do
	-- We already waited one second as a simple rate limiter.
	-- Next, wait until at least one change has been made.
	cs <- getChanges changechan
	-- Now see if now's a good time to commit.
	time <- getCurrentTime
	if shouldCommit time cs
		then do
			handleAdds st changechan cs
			void $ tryIO $ runThreadState st commitStaged
		else refillChanges changechan cs

commitStaged :: Annex ()
commitStaged = do
	Annex.Queue.flush
	inRepo $ Git.Command.run "commit"
		[ Param "--allow-empty-message"
		, Param "-m", Param ""
		-- Empty commits may be made if tree changes cancel
		-- each other out, etc
		, Param "--allow-empty"
		-- Avoid running the usual git-annex pre-commit hook;
		-- watch does the same symlink fixing, and we don't want
		-- to deal with unlocked files in these commits.
		, Param "--quiet"
		]

{- Decide if now is a good time to make a commit.
 - Note that the list of change times has an undefined order.
 -
 - Current strategy: If there have been 10 changes within the past second,
 - a batch activity is taking place, so wait for later.
 -}
shouldCommit :: UTCTime -> [Change] -> Bool
shouldCommit now changes
	| len == 0 = False
	| len > 10000 = True -- avoid bloating queue too much
	| length (filter thisSecond changes) < 10 = True
	| otherwise = False -- batch activity
	where
		len = length changes
		thisSecond c = now `diffUTCTime` changeTime c <= 1

{- If there are PendingAddChanges, the files have not yet actually been
 - added to the annex (probably), and that has to be done now, before
 - committing.
 -
 - Deferring the adds to this point causes batches to be bundled together,
 - which allows faster checking with lsof that the files are not still open
 - for write by some other process.
 -
 - When a file is added, Inotify will notice the new symlink. So this waits
 - for additional Changes to arrive, so that the symlink has hopefully been
 - staged before returning, and will be committed.
 -}
handleAdds :: ThreadState -> ChangeChan -> [Change] -> IO ()
handleAdds st changechan cs
	| null toadd = noop
	| otherwise = do
		toadd' <- safeToAdd st toadd
		unless (null toadd') $ do
			added <- filter id <$> forM toadd' add
			unless (null added) $
				handleAdds st changechan =<< getChanges changechan
	where
		toadd = map changeFile $ filter isPendingAdd cs

		isPendingAdd (Change { changeType = PendingAddChange }) = True
		isPendingAdd _ = False

		add keysource = catchBoolIO $ runThreadState st $ do
			showStart "add" $ keyFilename keysource
			handle (keyFilename keysource)
				=<< Command.Add.ingest keysource

		handle _ Nothing = do
			showEndFail
			return False
		handle file (Just key) = do
			Command.Add.link file key True
			showEndOk
			return True

{- Checks which of a set of files can safely be added.
 - Files are locked down as hard links in a temp directory,
 - with their write bits disabled. But some may have already
 - been opened for write, so lsof is run on the temp directory
 - to check them.
 -}
safeToAdd :: ThreadState -> [FilePath] -> IO [KeySource]
safeToAdd st files = do
	locked <- catMaybes <$> lockdown files
	runThreadState st $ do
		tmpdir <- fromRepo gitAnnexTmpDir
		open <- S.fromList . map fst3 . filter openwrite <$>
			liftIO (Lsof.queryDir tmpdir)
		catMaybes <$> forM locked (go open)
	where
		go open keysource
			| S.member (contentLocation keysource) open = do
				warning $ keyFilename keysource
					++ " still has writers, not adding"
				-- remove the hard link
				--_ <- liftIO $ tryIO $
				--	removeFile $ contentLocation keysource
				return Nothing
			| otherwise = return $ Just keysource

		lockdown = mapM $ \file -> do
			ms <- catchMaybeIO $ getSymbolicLinkStatus file
			case ms of
				Just s
					| isRegularFile s -> 
						catchMaybeIO $ runThreadState st $
							Command.Add.lockDown file
				_ -> return Nothing
	

		openwrite (_file, mode, _pid) =
			mode == Lsof.OpenWriteOnly || mode == Lsof.OpenReadWrite