{- git-annex command
 -
 - Copyright 2011 Joey Hess <joey@kitenet.net>
 - Copyright 2011 Joachim Breitner <mail@joachim-breitner.de>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Command.Sync where

import Common.Annex
import Command
import qualified Remote
import qualified Annex
import qualified Annex.Branch
import qualified Annex.Queue
import Annex.Content
import Annex.CatFile
import qualified Git.Command
import qualified Git.LsFiles as LsFiles
import qualified Git.Merge
import qualified Git.Branch
import qualified Git.Ref
import qualified Git
import Git.Types (BlobType(..))
import qualified Types.Remote
import qualified Remote.Git
import Types.Key
import Config

import qualified Data.ByteString.Lazy as L
import Data.Hash.MD5

def :: [Command]
def = [command "sync" (paramOptional (paramRepeating paramRemote))
	[seek] "synchronize local repository with remotes"]

-- syncing involves several operations, any of which can independently fail
seek :: CommandSeek
seek rs = do
	branch <- fromMaybe nobranch <$> inRepo Git.Branch.current
	remotes <- syncRemotes rs
	return $ concat
		[ [ commit ]
		, [ mergeLocal branch ]
		, [ pullRemote remote branch | remote <- remotes ]
		, [ mergeAnnex ]
		, [ pushLocal branch ]
		, [ pushRemote remote branch | remote <- remotes ]
		]
	where
		nobranch = error "no branch is checked out"

syncBranch :: Git.Ref -> Git.Ref
syncBranch = Git.Ref.under "refs/heads/synced/"

remoteBranch :: Remote -> Git.Ref -> Git.Ref
remoteBranch remote = Git.Ref.under $ "refs/remotes/" ++ Remote.name remote

syncRemotes :: [String] -> Annex [Remote]
syncRemotes rs = ifM (Annex.getState Annex.fast) ( nub <$> pickfast , wanted )
	where
		pickfast = (++) <$> listed <*> (good =<< fastest <$> available)
		wanted
			| null rs = good =<< concat . Remote.byCost <$> available
			| otherwise = listed
		listed = do
			l <- catMaybes <$> mapM (Remote.byName . Just) rs
			let s = filter Remote.specialRemote l
			unless (null s) $
				error $ "cannot sync special remotes: " ++
					unwords (map Types.Remote.name s)
			return l
		available = filter (not . Remote.specialRemote)
			<$> (filterM (repoSyncable . Types.Remote.repo)
				=<< Remote.enabledRemoteList)
		good = filterM $ Remote.Git.repoAvail . Types.Remote.repo
		fastest = fromMaybe [] . headMaybe . Remote.byCost

commit :: CommandStart
commit = do
	showStart "commit" ""
	next $ next $ do
		showOutput
		Annex.Branch.commit "update"
		-- Commit will fail when the tree is clean, so ignore failure.
		_ <- inRepo $ Git.Command.runBool "commit"
			[Param "-a", Param "-m", Param "git-annex automatic sync"]
		return True

mergeLocal :: Git.Ref -> CommandStart
mergeLocal branch = go =<< needmerge
	where
		syncbranch = syncBranch branch
		needmerge = do
			unlessM (inRepo $ Git.Ref.exists syncbranch) $
				inRepo $ updateBranch syncbranch
			inRepo $ Git.Branch.changed branch syncbranch
		go False = stop
		go True = do
			showStart "merge" $ Git.Ref.describe syncbranch
			next $ next $ mergeFrom syncbranch

pushLocal :: Git.Ref -> CommandStart
pushLocal branch = do
	inRepo $ updateBranch $ syncBranch branch
	stop

updateBranch :: Git.Ref -> Git.Repo -> IO ()
updateBranch syncbranch g = 
	unlessM go $ error $ "failed to update " ++ show syncbranch
	where
		go = Git.Command.runBool "branch"
			[ Param "-f"
			, Param $ show $ Git.Ref.base syncbranch
			] g

pullRemote :: Remote -> Git.Ref -> CommandStart
pullRemote remote branch = do
	showStart "pull" (Remote.name remote)
	next $ do
		showOutput
		stopUnless fetch $
			next $ mergeRemote remote (Just branch)
	where
		fetch = inRepo $ Git.Command.runBool "fetch"
			[Param $ Remote.name remote]

{- The remote probably has both a master and a synced/master branch.
 - Which to merge from? Well, the master has whatever latest changes
 - were committed, while the synced/master may have changes that some
 - other remote synced to this remote. So, merge them both. -}
mergeRemote :: Remote -> (Maybe Git.Ref) -> CommandCleanup
mergeRemote remote b = case b of
	Nothing -> do
		branch <- inRepo Git.Branch.currentUnsafe
		all id <$> (mapM merge $ branchlist branch)
	Just _ -> all id <$> (mapM merge =<< tomerge (branchlist b))
	where
		merge = mergeFrom . remoteBranch remote
		tomerge branches = filterM (changed remote) branches
		branchlist Nothing = []
		branchlist (Just branch) = [branch, syncBranch branch]

pushRemote :: Remote -> Git.Ref -> CommandStart
pushRemote remote branch = go =<< needpush
	where
		needpush = anyM (newer remote) [syncBranch branch, Annex.Branch.name]
		go False = stop
		go True = do
			showStart "push" (Remote.name remote)
			next $ next $ do
				showOutput
				inRepo $ pushBranch remote branch

pushBranch :: Remote -> Git.Ref -> Git.Repo -> IO Bool
pushBranch remote branch g =
	Git.Command.runBool "push"
		[ Param $ Remote.name remote
		, Param $ refspec Annex.Branch.name
		, Param $ refspec branch
		] g
	where
		refspec b = concat 
			[ show $ Git.Ref.base b
			,  ":"
			, show $ Git.Ref.base $ syncBranch b
			]

mergeAnnex :: CommandStart
mergeAnnex = do
	void $ Annex.Branch.forceUpdate
	stop

mergeFrom :: Git.Ref -> Annex Bool
mergeFrom branch = do
	showOutput
	ok <- inRepo $ Git.Merge.mergeNonInteractive branch
	if ok
		then return ok
		else resolveMerge

{- Resolves a conflicted merge. It's important that any conflicts be
 - resolved in a way that itself avoids later merge conflicts, since
 - multiple repositories may be doing this concurrently.
 -
 - Only annexed files are resolved; other files are left for the user to
 - handle.
 -
 - This uses the Keys pointed to by the files to construct new
 - filenames. So when both sides modified file foo, 
 - it will be deleted, and replaced with files foo.KEYA and foo.KEYB.
 -
 - On the other hand, when one side deleted foo, and the other modified it,
 - it will be deleted, and the modified version stored as file
 - foo.KEYA (or KEYB).
 -}
resolveMerge :: Annex Bool
resolveMerge = do
	top <- fromRepo Git.repoPath
	(fs, cleanup) <- inRepo (LsFiles.unmerged [top])
	merged <- all id <$> mapM resolveMerge' fs
	when merged $ do
		Annex.Queue.flush
		void $ inRepo $ Git.Command.runBool "commit"
			[Param "-m", Param "git-annex automatic merge conflict fix"]
	void $ liftIO cleanup
	return merged

resolveMerge' :: LsFiles.Unmerged -> Annex Bool
resolveMerge' u
	| issymlink LsFiles.valUs && issymlink LsFiles.valThem =
		withKey LsFiles.valUs $ \keyUs ->
		withKey LsFiles.valThem $ \keyThem -> go keyUs keyThem
	| otherwise = return False
	where
		go keyUs keyThem
			| keyUs == keyThem = do
				makelink keyUs
				return True
			| otherwise = do
				liftIO $ nukeFile file
				Annex.Queue.addCommand "rm" [Params "--quiet -f --"] [file]
				makelink keyUs
				makelink keyThem
				return True
		file = LsFiles.unmergedFile u
		issymlink select = any (select (LsFiles.unmergedBlobType u) ==)
			[Just SymlinkBlob, Nothing]
		makelink (Just key) = do
			let dest = mergeFile file key
			l <- calcGitLink dest key
			liftIO $ do
				nukeFile dest
				createSymbolicLink l dest
			Annex.Queue.addCommand "add" [Param "--force", Param "--"] [dest]
		makelink _ = noop
		withKey select a = do
			let msha = select $ LsFiles.unmergedSha u
			case msha of
				Nothing -> a Nothing
				Just sha -> do
					key <- fileKey . takeFileName
						. encodeW8 . L.unpack 
						<$> catObject sha
					maybe (return False) (a . Just) key

{- The filename to use when resolving a conflicted merge of a file,
 - that points to a key.
 -
 - Something derived from the key needs to be included in the filename,
 - but rather than exposing the whole key to the user, a very weak hash
 - is used. There is a very real, although still unlikely, chance of
 - conflicts using this hash.
 -
 - In the event that there is a conflict with the filename generated
 - for some other key, that conflict will itself be handled by the
 - conflicted merge resolution code. That case is detected, and the full
 - key is used in the filename.
 -}
mergeFile :: FilePath -> Key -> FilePath
mergeFile file key
	| doubleconflict = go $ key2file key
	| otherwise = go $ shortHash $ key2file key
	where
		varmarker = ".variant-"
		doubleconflict = varmarker `isSuffixOf` (dropExtension file)
		go v = takeDirectory file
			</> dropExtension (takeFileName file)
			++ varmarker ++ v
			++ takeExtension file
		
shortHash :: String -> String
shortHash = take 4 . md5s . md5FilePath

changed :: Remote -> Git.Ref -> Annex Bool
changed remote b = do
	let r = remoteBranch remote b
	ifM (inRepo $ Git.Ref.exists r)
		( inRepo $ Git.Branch.changed b r
		, return False
		)

newer :: Remote -> Git.Ref -> Annex Bool
newer remote b = do
	let r = remoteBranch remote b
	ifM (inRepo $ Git.Ref.exists r)
		( inRepo $ Git.Branch.changed r b
		, return True
		)