{- management of the git-annex branch
 -
 - Copyright 2011 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Branch (
	create,
	update,
	get,
	change,
	commit,
	files,
	refExists,
	hasOrigin,
	name	
) where

import Control.Monad (when, unless, liftM)
import Control.Monad.State (liftIO)
import System.FilePath
import System.Directory
import Data.String.Utils
import System.Cmd.Utils
import Data.Maybe
import Data.List
import System.IO
import System.IO.Binary
import System.Posix.Process
import System.Exit
import qualified Data.ByteString.Char8 as B

import Types.BranchState
import qualified Git
import qualified Git.UnionMerge
import qualified Annex
import Utility
import Types
import Messages
import Locations

type GitRef = String

{- Name of the branch that is used to store git-annex's information. -}
name :: GitRef
name = "git-annex"

{- Fully qualified name of the branch. -}
fullname :: GitRef
fullname = "refs/heads/" ++ name

{- Branch's name in origin. -}
originname :: GitRef
originname = "origin/" ++ name

{- Converts a fully qualified git ref into a short version for human
 - consumptiom. -}
shortref :: GitRef -> String
shortref = remove "refs/heads/" . remove "refs/remotes/"
	where
		remove prefix s
			| prefix `isPrefixOf` s = drop (length prefix) s
			| otherwise = s

{- A separate index file for the branch. -}
index :: Git.Repo -> FilePath
index g = gitAnnexDir g </> "index"

{- Populates the branch's index file with the current branch contents.
 - 
 - Usually, this is only done when the index doesn't yet exist, and
 - the index is used to build up changes to be commited to the branch,
 - and merge in changes from other branches.
 -}
genIndex :: Git.Repo -> IO ()
genIndex g = Git.UnionMerge.ls_tree g fullname >>= Git.UnionMerge.update_index g

{- Runs an action using the branch's index file. -}
withIndex :: Annex a -> Annex a
withIndex = withIndex' False
withIndex' :: Bool -> Annex a -> Annex a
withIndex' bootstrapping a = do
	g <- Annex.gitRepo
	let f = index g
	reset <- liftIO $ Git.useIndex f

	e <- liftIO $ doesFileExist f
	unless e $ do
		unless bootstrapping $ create
		liftIO $ createDirectoryIfMissing True $ takeDirectory f
		liftIO $ unless bootstrapping $ genIndex g

	r <- a
	liftIO reset
	return r

withIndexUpdate :: Annex a -> Annex a
withIndexUpdate a = update >> withIndex a

getState :: Annex BranchState
getState = Annex.getState Annex.branchstate

setState :: BranchState -> Annex ()
setState state = Annex.changeState $ \s -> s { Annex.branchstate = state }

setCache :: FilePath -> String -> Annex ()
setCache file content = do
	state <- getState
	setState state { cachedFile = Just file, cachedContent = content }

invalidateCache :: Annex ()
invalidateCache = do
	state <- getState
	setState state { cachedFile = Nothing, cachedContent = "" }

getCache :: FilePath -> Annex (Maybe String)
getCache file = getState >>= handle
	where
		handle state
			| cachedFile state == Just file =
				return $ Just $ cachedContent state
			| otherwise = return Nothing

{- Creates the branch, if it does not already exist. -}
create :: Annex ()
create = unlessM (refExists fullname) $ do
	g <- Annex.gitRepo
	e <- hasOrigin
	if e
		then liftIO $ Git.run g "branch" [Param name, Param originname]
		else withIndex' True $
			liftIO $ Git.commit g "branch created" fullname []

{- Stages the journal, and commits staged changes to the branch. -}
commit :: String -> Annex ()
commit message = whenM stageJournalFiles $ do
	g <- Annex.gitRepo
	withIndex $ liftIO $ Git.commit g message fullname [fullname]

{- 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
	state <- getState
	unless (branchUpdated state) $ withIndex $ do
		{- Since branches get merged into the index, it's important to
		 - first stage the journal into the index. Otherwise, any
		 - changes in the journal would later get staged, and might
		 - overwrite changes made during the merge.
		 -
		 - It would be cleaner to handle the merge by updating the
		 - journal, not the index, with changes from the branches.
		 -}
		staged <- stageJournalFiles

		g <- Annex.gitRepo
		r <- liftIO $ Git.pipeRead g [Param "show-ref", Param name]
		let refs = map (last . words) (lines r)
		updated <- catMaybes `liftM` mapM updateRef refs
		unless (null updated && not staged) $ liftIO $
			Git.commit g "update" fullname (fullname:updated)
		Annex.changeState $ \s -> s { Annex.branchstate = state { branchUpdated = True } }
		invalidateCache

{- Does origin/git-annex exist? -}
hasOrigin :: Annex Bool
hasOrigin = refExists originname

{- Checks if a git ref exists. -}
refExists :: GitRef -> Annex Bool
refExists ref = do
	g <- Annex.gitRepo
	liftIO $ Git.runBool g "show-ref"
		[Param "--verify", Param "-q", Param ref]

{- Ensures that a given ref has been merged into the index. -}
updateRef :: GitRef -> Annex (Maybe String)
updateRef ref
	| ref == fullname = return Nothing
	| otherwise = do
		g <- Annex.gitRepo
		-- checking with log to see if there have been changes
		-- is less expensive than always merging
		diffs <- liftIO $ Git.pipeRead g [
			Param "log",
			Param (name++".."++ref),
			Params "--oneline -n1"
			]
		if (null diffs)
			then return Nothing
			else do
				showSideAction $ "merging " ++ shortref ref ++ " into " ++ name ++ "..."
				-- By passing only one ref, it is actually
				-- merged into the index, preserving any
				-- changes that may already be staged.
				--
				-- However, any changes in the git-annex
				-- branch that are *not* reflected in the
				-- index will be removed. So, documentation
				-- advises users not to directly modify the
				-- branch.
				liftIO $ Git.UnionMerge.merge g [ref]
				return $ Just ref

{- Records changed content of a file into the journal. -}
change :: FilePath -> String -> Annex ()
change file content = do
	setJournalFile file content
	setCache file content

{- Gets the content of a file on the branch, or content from the journal, or
 - staged in the index.
 -
 - Returns an empty string if the file doesn't exist yet. -}
get :: FilePath -> Annex String
get file = do
	cached <- getCache file
	case cached of
		Just content -> return content
		Nothing -> do
			j <- getJournalFile file
			case j of
				Just content -> do
					setCache file content
					return content
				Nothing -> withIndexUpdate $ do
					content <- catFile file
					setCache file content
					return content

{- Uses git cat-file in batch mode to read the content of a file.
 -
 - Only one process is run, and it persists and is used for all accesses. -}
catFile :: FilePath -> Annex String
catFile file = do
	state <- getState
	maybe (startup state) ask (catFileHandles state)
	where
		startup state = do
			g <- Annex.gitRepo
			(_, from, to) <- liftIO $ hPipeBoth "git" $
				toCommand $ Git.gitCommandLine g
					[Param "cat-file", Param "--batch"]
			setState state { catFileHandles = Just (from, to) }
			ask (from, to)
		ask (from, to) = liftIO $ do
			let want = fullname ++ ":" ++ file
			hPutStrLn to want
			hFlush to
			header <- hGetLine from
			case words header of
				[sha, blob, size]
					| length sha == Git.shaSize &&
					  blob == "blob" -> handle from size
					| otherwise -> empty
				_
					| header == want ++ " missing" -> empty
					| otherwise -> error $ "unknown response from git cat-file " ++ header
		handle from size = case reads size of
			[(bytes, "")] -> readcontent from bytes
			_ -> empty
		readcontent from bytes = do
			content <- B.hGet from bytes
			c <- hGetChar from
			when (c /= '\n') $
				error "missing newline from git cat-file"
			return $ B.unpack content
		empty = return ""

{- Lists all files on the branch. There may be duplicates in the list. -}
files :: Annex [FilePath]
files = withIndexUpdate $ do
	g <- Annex.gitRepo
	bfiles <- liftIO $ Git.pipeNullSplit g
		[Params "ls-tree --name-only -r -z", Param fullname]
	jfiles <- getJournalFiles
	return $ jfiles ++ bfiles

{- Records content for a file in the branch to the journal.
 -
 - Using the journal, rather than immediatly staging content to the index
 - avoids git needing to rewrite the index after every change. -}
setJournalFile :: FilePath -> String -> Annex ()
setJournalFile file content = do
	g <- Annex.gitRepo
	liftIO $ catch (write g) $ const $ do
		createDirectoryIfMissing True $ gitAnnexJournalDir g
		createDirectoryIfMissing True $ gitAnnexTmpDir g
		write g
	where
		-- journal file is written atomically
		write g = do
			let jfile = journalFile g file
			let tmpfile = gitAnnexTmpDir g </> takeFileName jfile
			writeBinaryFile tmpfile content
			renameFile tmpfile jfile

{- Gets journalled content for a file in the branch. -}
getJournalFile :: FilePath -> Annex (Maybe String)
getJournalFile file = do
	g <- Annex.gitRepo
	liftIO $ catch (liftM Just . readFileStrict $ journalFile g file)
		(const $ return Nothing)

{- List of journal files. -}
getJournalFiles :: Annex [FilePath]
getJournalFiles = getJournalFilesRaw >>= return . map fileJournal

getJournalFilesRaw :: Annex [FilePath]
getJournalFilesRaw = do
	g <- Annex.gitRepo
	fs <- liftIO $ catch (getDirectoryContents $ gitAnnexJournalDir g)
		(const $ return [])
	return $ filter (\f -> f /= "." && f /= "..") fs

{- Stages all journal files into the index, and returns True if the index
 - was modified. -}
stageJournalFiles :: Annex Bool
stageJournalFiles = do
	l <- getJournalFilesRaw
	if null l
		then return False
		else do
			g <- Annex.gitRepo
			withIndex $ liftIO $ stage g l
			return True
	where
		stage g fs = do
			let dir = gitAnnexJournalDir g
			let paths = map (dir </>) fs
			-- inject all the journal files directly into git
			-- in one quick command
			(pid, fromh, toh) <- hPipeBoth "git" $ toCommand $
				Git.gitCommandLine g [Param "hash-object", Param "-w", Param "--stdin-paths"]
			_ <- forkProcess $ do
				hPutStr toh $ unlines paths
				hClose toh
				exitSuccess
			hClose toh
			s <- hGetContents fromh
			-- update the index, also in just one command
			Git.UnionMerge.update_index g $
				index_lines (lines s) $ map fileJournal fs
			hClose fromh
			forceSuccess pid
			mapM_ removeFile paths
		index_lines shas fs = map genline $ zip shas fs
		genline (sha, file) = Git.UnionMerge.update_index_line sha file

{- Produces a filename to use in the journal for a file on the branch.
 -
 - The journal typically won't have a lot of files in it, so the hashing
 - used in the branch is not necessary, and all the files are put directly
 - in the journal directory.
 -}
journalFile :: Git.Repo -> FilePath -> FilePath
journalFile repo file = gitAnnexJournalDir repo </> concatMap mangle file
	where
		mangle '/' = "_"
		mangle '_' = "__"
		mangle c = [c]

{- Converts a journal file (relative to the journal dir) back to the
 - filename on the branch. -}
fileJournal :: FilePath -> FilePath
fileJournal = replace "//" "_" . replace "_" "/"