{- Temporarily changing the files git uses.
 -
 - Copyright 2014-2016 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Annex.GitOverlay where

import qualified Control.Exception as E

import Annex.Common
import Git
import Git.Types
import Git.Index
import Git.Env
import qualified Annex
import qualified Annex.Queue

{- Runs an action using a different git index file. -}
withIndexFile :: FilePath -> Annex a -> Annex a
withIndexFile f a = do
	f' <- liftIO $ indexEnvVal f
	withAltRepo
		(usecachedgitenv $ \g -> liftIO $ addGitEnv g indexEnv f')
		(\g g' -> g' { gitEnv = gitEnv g })
		a
  where
	-- This is an optimisation. Since withIndexFile is run repeatedly,
	-- and addGitEnv uses the slow copyGitEnv when gitEnv is Nothing, 
	-- we cache the copied environment the first time, and reuse it in
	-- subsequent calls.
	--
	-- (This could be done at another level; eg when creating the
	-- Git object in the first place, but it's more efficient to let
	-- the enviroment be inherited in all calls to git where it
	-- does not need to be modified.)
	usecachedgitenv m g = case gitEnv g of
		Just _ -> m g
		Nothing -> do
			e <- Annex.withState $ \s -> case Annex.cachedgitenv s of
				Nothing -> do
					e <- copyGitEnv
					return (s { Annex.cachedgitenv = Just e }, e)
				Just e -> return (s, e)
			m (g { gitEnv = Just e })

{- Runs an action using a different git work tree.
 -
 - Smudge and clean filters are disabled in this work tree. -}
withWorkTree :: FilePath -> Annex a -> Annex a
withWorkTree d = withAltRepo
	(\g -> return $ g { location = modlocation (location g), gitGlobalOpts = gitGlobalOpts g ++ disableSmudgeConfig })
	(\g g' -> g' { location = location g, gitGlobalOpts = gitGlobalOpts g })
  where
	modlocation l@(Local {}) = l { worktree = Just d }
	modlocation _ = error "withWorkTree of non-local git repo"
	disableSmudgeConfig = map Param
		[ "-c", "filter.annex.smudge="
		, "-c", "filter.annex.clean="
		]

{- Runs an action with the git index file and HEAD, and a few other
 - files that are related to the work tree coming from an overlay
 - directory other than the usual. This is done by pointing
 - GIT_COMMON_DIR at the regular git directory, and GIT_DIR at the
 - overlay directory.
 -
 - Needs git 2.2.0 or newer.
 -}
withWorkTreeRelated :: FilePath -> Annex a -> Annex a
withWorkTreeRelated d = withAltRepo modrepo unmodrepo
  where
	modrepo g = liftIO $ do
		g' <- addGitEnv g "GIT_COMMON_DIR" =<< absPath (localGitDir g)
		g'' <- addGitEnv g' "GIT_DIR" d
		return (g'' { gitEnvOverridesGitDir = True })
	unmodrepo g g' = g'
		{ gitEnv = gitEnv g
		, gitEnvOverridesGitDir = gitEnvOverridesGitDir g
		}

withAltRepo 
	:: (Repo -> Annex Repo)
	-- ^ modify Repo
	-> (Repo -> Repo -> Repo)
	-- ^ undo modifications; first Repo is the original and second
	-- is the one after running the action.
	-> Annex a
	-> Annex a
withAltRepo modrepo unmodrepo a = do
	g <- gitRepo
	g' <- modrepo g
	q <- Annex.Queue.get
	v <- tryNonAsync $ do
		Annex.changeState $ \s -> s
			{ Annex.repo = g'
			-- Start a separate queue for any changes made
			-- with the modified repo.
			, Annex.repoqueue = Nothing
			}
		a
	void $ tryNonAsync Annex.Queue.flush
	Annex.changeState $ \s -> s
		{ Annex.repo = unmodrepo g (Annex.repo s)
		, Annex.repoqueue = Just q
		}
	either E.throw return v