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+{- git-annex branch management
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Branch where
+
+import Control.Monad (unless)
+import Control.Monad.State (liftIO)
+
+import GitUnionMerge
+import GitRepo as Git
+import qualified Annex
+import Utility
+import Types
+import Messages
+
+name :: String
+name = "git-annex"
+
+fullname :: String
+fullname = "refs/heads/" ++ name
+
+{- Ensures that the branch is up-to-date; should be called before
+ - data is read from it. Runs only once per git-annex run. -}
+update :: Annex ()
+update = do
+	updated <- Annex.getState Annex.updated
+	unless updated $ do
+		g <- Annex.gitRepo
+		refs <- liftIO $ Git.pipeRead g [Param "show-ref", Param name]
+		mapM_ updateRef $ map (last . words) (lines refs)
+		Annex.changeState $ \s -> s { Annex.updated = True }
+
+{- Ensures that a given ref has been merged into the local git-annex branch. -}
+updateRef :: String -> Annex ()
+updateRef ref
+	| ref == fullname = return ()
+	| otherwise = do
+		g <- Annex.gitRepo
+		diffs <- liftIO $ Git.pipeRead g [
+			Param "log",
+			Param (name++".."++ref),
+			Params "--oneline -n1"
+			]
+		unless (null diffs) $ do
+			showSideAction "merging " ++ ref ++ " into " ++ name ++ "..."
+			liftIO $ unionMerge g fullname ref fullname