{- git-annex assistant git merge thread
 -
 - Copyright 2012 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Assistant.Merger where

import Common.Annex
import Assistant.ThreadedMonad
import Utility.DirWatcher
import Utility.Types.DirWatcher
import qualified Git
import qualified Git.Command
import qualified Git.Branch
import qualified Command.Sync

{- This thread watches for changes to .git/refs/heads/synced/*,
 - which indicate incoming pushes. It merges those pushes into the
 - currently checked out branch. -}
mergeThread :: ThreadState -> IO ()
mergeThread st = do
	g <- runThreadState st $ fromRepo id
	let dir = Git.localGitDir g </> "refs" </> "heads" </> "synced"
	createDirectoryIfMissing True dir
	let hook a = Just $ runHandler g a
	let hooks = mkWatchHooks
		{ addHook = hook onAdd
		, errHook = hook onErr
		}
	watchDir dir (const False) hooks id
	where

type Handler = Git.Repo -> FilePath -> Maybe FileStatus -> IO ()

{- Runs an action handler.
 -
 - Exceptions are ignored, otherwise a whole thread could be crashed.
 -}
runHandler :: Git.Repo -> Handler -> FilePath -> Maybe FileStatus -> IO ()
runHandler g handler file filestatus = void $ do
        either print (const noop) =<< tryIO go
        where
                go = handler g file filestatus

{- Called when there's an error with inotify. -}
onErr :: Handler
onErr _ msg _ = error msg

{- Called when a new branch ref is written.
 -
 - This relies on git's atomic method of updating branch ref files,
 - which is to first write the new file to .lock, and then rename it
 - over the old file. So, ignore .lock files, and the rename ensures
 - the watcher sees a new file being added on each update.
 -
 - At startup, synthetic add events fire, causing this to run, but that's
 - ok; it ensures that any changes pushed since the last time the assistant
 - ran are merged in.
 -}
onAdd :: Handler
onAdd g file _
	| ".lock" `isSuffixOf` file = noop
	| otherwise = do
		let branch = Git.Ref $ "refs" </> "heads" </> takeFileName file
		current <- Git.Branch.current g
		when (Just branch == current) $
			void $ mergeBranch branch g

mergeBranch :: Git.Ref -> Git.Repo -> IO Bool
mergeBranch branch = Git.Command.runBool "merge"
	[Param $ show $ Command.Sync.syncBranch branch]