{- git-union-merge program
 -
 - Copyright 2011 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

import System.Environment

import Common
import qualified Git.UnionMerge
import qualified Git

header :: String
header = "Usage: git-union-merge ref ref newref"

usage :: IO a
usage = error $ "bad parameters\n\n" ++ header

tmpIndex :: Git.Repo -> FilePath
tmpIndex g = Git.gitDir g </> "index.git-union-merge"

setup :: Git.Repo -> IO ()
setup = cleanup -- idempotency

cleanup :: Git.Repo -> IO ()
cleanup g = do
	e' <- doesFileExist (tmpIndex g)
	when e' $ removeFile (tmpIndex g)

parseArgs :: IO [String]
parseArgs = do
	args <- getArgs
	if length args /= 3
		then usage
		else return args

main :: IO ()
main = do
	[aref, bref, newref] <- map Git.Ref <$> parseArgs
	g <- Git.configRead =<< Git.repoFromCwd
	_ <- Git.useIndex (tmpIndex g)
	setup g
	Git.UnionMerge.merge aref bref g
	_ <- Git.commit "union merge" newref [aref, bref] g
	cleanup g