{- 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,
	hasSomeBranch,
	name	
) where

import Control.Monad (when, unless, liftM)
import Control.Monad.State (liftIO)
import Control.Applicative ((<$>))
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 Utility.Conditional
import Utility.SafeCommand
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 hasBranch $ 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

		refs <- siblingBranches
		updated <- catMaybes <$> mapM updateRef refs
		g <- Annex.gitRepo
		unless (null updated && not staged) $ liftIO $
			Git.commit g "update" fullname (fullname:updated)
		Annex.changeState $ \s -> s { Annex.branchstate = state { branchUpdated = True } }
		invalidateCache

{- 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]

{- Does the main git-annex branch exist? -}
hasBranch :: Annex Bool
hasBranch = refExists fullname

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

{- Does the git-annex branch or a foo/git-annex branch exist? -}
hasSomeBranch :: Annex Bool
hasSomeBranch = not . null <$> siblingBranches

{- List of all git-annex branches, including the main one and any
 - from remotes. -}
siblingBranches :: Annex [String]
siblingBranches = do
	g <- Annex.gitRepo
	r <- liftIO $ Git.pipeRead g [Param "show-ref", Param name]
	return $ map (last . words) (lines r)

{- 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 = map fileJournal <$> getJournalFilesRaw

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 "_" "/"