{- git trees
 -
 - Copyright 2016-2021 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

{-# LANGUAGE BangPatterns, TypeSynonymInstances, FlexibleInstances #-}

module Git.Tree (
	Tree(..),
	TreeContent(..),
	getTree,
	recordTree,
	recordTree',
	recordSubTree,
	TreeItem(..),
	treeItemsToTree,
	treeItemToLsTreeItem,
	lsTreeItemToTreeItem,
	adjustTree,
	graftTree,
	graftTree',
	withMkTreeHandle,
	MkTreeHandle,
	treeMode,
) where

import Common
import Git
import Git.FilePath
import Git.Types
import Git.Command
import Git.Sha
import qualified Git.LsTree as LsTree
import qualified Utility.CoProcess as CoProcess
import qualified System.FilePath.ByteString as P

import Numeric
import System.Posix.Types
import Control.Monad.IO.Class
import qualified Data.Set as S
import qualified Data.Map as M
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as S8

newtype Tree = Tree [TreeContent]
	deriving (Show)

data TreeContent
	-- A blob object in the tree.
	= TreeBlob TopFilePath FileMode Sha
	-- A subtree that is already recorded in git, with a known sha.
	| RecordedSubTree TopFilePath Sha [TreeContent]
	-- A subtree that has not yet been recorded in git.
	| NewSubTree TopFilePath [TreeContent]
	-- A commit object that is part of a tree (used for submodules)
	| TreeCommit TopFilePath FileMode Sha
	deriving (Show, Eq, Ord)

{- Gets the Tree for a Ref. -}
getTree :: LsTree.LsTreeRecursive -> Ref -> Repo -> IO Tree
getTree recursive r repo = do
	(l, cleanup) <- lsTreeWithObjects recursive r repo
	let !t = either (\e -> giveup ("ls-tree parse error:" ++ e)) id
		(extractTree l)
	void cleanup
	return t

lsTreeWithObjects :: LsTree.LsTreeRecursive -> Ref -> Repo -> IO ([LsTree.TreeItem], IO Bool)
lsTreeWithObjects recursive = 
	LsTree.lsTree' [Param "-t"] recursive (LsTree.LsTreeLong False)

newtype MkTreeHandle = MkTreeHandle CoProcess.CoProcessHandle

withMkTreeHandle :: (MonadIO m, MonadMask m) => Repo -> (MkTreeHandle -> m a) -> m a
withMkTreeHandle repo a = bracketIO setup cleanup (a . MkTreeHandle)
  where
	setup = gitCoProcessStart False ps repo
	ps = [Param "mktree", Param "--missing", Param "--batch", Param "-z"]
	cleanup = CoProcess.stop

{- Records a Tree in the Repo, returning its Sha.
 - 
 - Efficiently handles subtrees, by only recording ones that have not
 - already been recorded before. And even when many subtrees need to be
 - recorded, it's done with a single call to git mktree, using its batch
 - interface.
 -}
recordTree :: Tree -> Repo -> IO Sha
recordTree t repo = withMkTreeHandle repo $ \h -> recordTree' h t

recordTree' :: MkTreeHandle -> Tree -> IO Sha
recordTree' h (Tree l) = mkTree h =<< mapM (recordSubTree h) l

{- Note that the returned RecordedSubTree does not have its [TreeContent]
 - list populated. This is a memory optimisation, since the list is not
 - used. -}
recordSubTree :: MkTreeHandle -> TreeContent -> IO TreeContent
recordSubTree h (NewSubTree d l) = do
	sha <- mkTree h =<< mapM (recordSubTree h) l
	return (RecordedSubTree d sha [])
recordSubTree _ alreadyrecorded = return alreadyrecorded
 
mkTree :: MkTreeHandle -> [TreeContent] -> IO Sha
mkTree (MkTreeHandle cp) l = CoProcess.query cp send receive
  where
	send h = do
		forM_ l $ \i ->	hPutStr h $ case i of
			TreeBlob f fm s -> mkTreeOutput fm BlobObject s f
			RecordedSubTree f s _ -> mkTreeOutput treeMode TreeObject s f
			NewSubTree _ _ -> error "recordSubTree internal error; unexpected NewSubTree"
			TreeCommit f fm s -> mkTreeOutput fm CommitObject s f
		hPutStr h "\NUL" -- signal end of tree to --batch
	receive h = getSha "mktree" (S8.hGetLine h)

treeMode :: FileMode
treeMode = 0o040000

mkTreeOutput :: FileMode -> ObjectType -> Sha -> TopFilePath -> String
mkTreeOutput fm ot s f = concat
	[ showOct fm ""
	, " "
	, decodeBS (fmtObjectType ot)
	, " "
	, fromRef s
	, "\t"
	, takeFileName (fromRawFilePath (getTopFilePath f))
	, "\NUL"
	]

data TreeItem = TreeItem TopFilePath FileMode Sha
	deriving (Show, Eq)

treeItemToTreeContent :: TreeItem -> TreeContent
treeItemToTreeContent (TreeItem f m s) = case toTreeItemType m of
	Just TreeSubmodule -> TreeCommit f m s
	_ -> TreeBlob f m s

treeItemToLsTreeItem :: TreeItem -> LsTree.TreeItem
treeItemToLsTreeItem (TreeItem f mode sha) = LsTree.TreeItem
	{ LsTree.mode = mode
	, LsTree.typeobj = fmtObjectType $ case toTreeItemType mode of
		Just TreeSubmodule -> CommitObject
		Just TreeSubtree -> TreeObject
		_ -> BlobObject
	, LsTree.sha = sha
	, LsTree.size = Nothing
	, LsTree.file = f
	}

lsTreeItemToTreeItem :: LsTree.TreeItem -> TreeItem
lsTreeItemToTreeItem ti = TreeItem
	(LsTree.file ti)
	(LsTree.mode ti)
	(LsTree.sha ti)

treeItemsToTree :: [TreeItem] -> Tree
treeItemsToTree = go M.empty
  where
	go m [] = Tree $ filter inTopTree (M.elems m)
	go m (i:is)
		| inTopTree p =
			go (M.insert p (treeItemToTreeContent i) m) is
		| otherwise = case M.lookup idir m of
			Just (NewSubTree d l) ->
				go (addsubtree idir m (NewSubTree d (c:l))) is
			_ ->
				go (addsubtree idir m (NewSubTree (asTopFilePath idir) [c])) is
	  where
		p = gitPath i
		idir = P.takeDirectory p
		c = treeItemToTreeContent i

	addsubtree d m t
		| not (inTopTree d) = 
			let m' = M.insert d t m
			in case M.lookup parent m' of
				Just (NewSubTree d' l) ->
					let l' = filter (\ti -> gitPath ti /= d) l
					in addsubtree parent m' (NewSubTree d' (t:l'))
				_ -> addsubtree parent m' (NewSubTree (asTopFilePath parent) [t])
		| otherwise = M.insert d t m
	  where
		parent = P.takeDirectory d

{- Flattens the top N levels of a Tree. -}
flattenTree :: Int -> Tree -> Tree
flattenTree 0 t = t
flattenTree n (Tree l) = Tree (concatMap (go n) l)
  where
	go 0 c = [c]
	go _ b@(TreeBlob _ _ _) = [b]
	go n' (RecordedSubTree _ _ l') = concatMap (go (n'-1)) l'
	go n' (NewSubTree _ l') = concatMap (go (n'-1)) l'
	go _ c@(TreeCommit _ _ _) = [c]

{- Applies an adjustment to items in a tree.
 -
 - While less flexible than using getTree and recordTree,
 - this avoids buffering the whole tree in memory.
 -}
adjustTree
	:: (Functor m, MonadIO m, MonadMask m)
	=> (TreeItem -> m (Maybe TreeItem))
	-- ^ Adjust an item in the tree. Nothing deletes the item.
	-- Cannot move the item to a different tree.
	-> [TreeItem]
	-- ^ New items to add to the tree.
	-> (TreeContent -> TreeContent -> TreeContent)
	-- ^ When adding a new item to the tree and an item with the same
	-- name already exists, this function picks which to use.
	-- The first one is the item that was already in the tree.
	-> [TopFilePath]
	-- ^ Files to remove from the tree.
	-> Ref
	-> Repo
	-> m Sha
adjustTree adjusttreeitem addtreeitems resolveaddconflict removefiles r repo =
	withMkTreeHandle repo $ \h -> do
		(l, cleanup) <- liftIO $ lsTreeWithObjects LsTree.LsTreeRecursive r repo
		(l', _, _) <- go h False [] 1 inTopTree l
		l'' <- adjustlist h 0 inTopTree (const True) l'
		sha <- liftIO $ mkTree h l''
		void $ liftIO cleanup
		return sha
  where
	go _ wasmodified c _ _ [] = return (c, wasmodified, [])
	go h wasmodified c depth intree (i:is)
		| intree i = case readObjectType (LsTree.typeobj i) of
			Just BlobObject -> do
				let ti = TreeItem (LsTree.file i) (LsTree.mode i) (LsTree.sha i)
				v <- adjusttreeitem ti
				case v of
					Nothing -> go h True c depth intree is
					Just ti'@(TreeItem f m s) ->
						let !modified = wasmodified || ti' /= ti
						    blob = TreeBlob f m s
						in go h modified (blob:c) depth intree is
			Just TreeObject -> do
				(sl, modified, is') <- go h False [] (depth+1) (beneathSubTree i) is
				sl' <- adjustlist h depth (inTree i) (beneathSubTree i) sl
				let slmodified = sl' /= sl
				subtree <- if modified || slmodified
					then liftIO $ recordSubTree h $ NewSubTree (LsTree.file i) sl'
					else return $ RecordedSubTree (LsTree.file i) (LsTree.sha i) [] 
				let !modified' = modified || slmodified || wasmodified
				go h modified' (subtree : c) depth intree is'
			Just CommitObject -> do
				let ti = TreeItem (LsTree.file i) (LsTree.mode i) (LsTree.sha i)
				v <- adjusttreeitem ti
				case v of
					Nothing -> go h True c depth intree is
					Just (TreeItem f m s) -> 
						let commit = TreeCommit f m s
						in go h wasmodified (commit:c) depth intree is
			_ -> giveup ("unexpected object type \"" ++ decodeBS (LsTree.typeobj i) ++ "\"")
		| otherwise = return (c, wasmodified, i:is)

	adjustlist h depth ishere underhere l = do
		let (addhere, rest) = partition ishere addtreeitems
		let l' = filter (not . removed) $
			addoldnew l (map treeItemToTreeContent addhere)
		let inl i = any (\t -> beneathSubTree t i) l'
		let (Tree addunderhere) = flattenTree depth $ treeItemsToTree $
			filter (\i -> underhere i && not (inl i)) rest
		addunderhere' <- liftIO $ mapM (recordSubTree h) addunderhere
		return (addoldnew l' addunderhere')

	removeset = S.fromList $ map (P.normalise . gitPath) removefiles
	removed (TreeBlob f _ _) = S.member (P.normalise (gitPath f)) removeset
	removed (TreeCommit f _ _) = S.member (P.normalise (gitPath f)) removeset
	removed (RecordedSubTree _ _ _) = False
	removed (NewSubTree _ _) = False

	addoldnew [] new = new
	addoldnew old [] = old
	addoldnew old new = addoldnew' (M.fromList $ map (\i -> (mkk i, i)) old) new
	addoldnew' oldm (n:ns) = 
			let k = mkk n
			in case M.lookup k oldm of
				Just o -> 
					resolveaddconflict o n
					: 
					addoldnew' (M.delete k oldm) ns
				Nothing -> n : addoldnew' oldm ns
	addoldnew' oldm [] = M.elems oldm
	mkk = P.normalise . gitPath

{- Grafts subtree into the basetree at the specified location, replacing
 - anything that the basetree already had at that location.
 -
 - This is generally much more efficient than using getTree and recordTree,
 - or adjustTree, since it only needs to traverse from the top of the tree
 - down to the graft location. It does not buffer the whole tree in memory.
 -}
graftTree
	:: Sha
	-> TopFilePath
	-> Sha
	-> Repo
	-> IO Sha
graftTree subtree graftloc basetree repo =
	withMkTreeHandle repo $ graftTree' subtree graftloc basetree repo

graftTree'
	:: Sha
	-> TopFilePath
	-> Sha
	-> Repo
	-> MkTreeHandle
	-> IO Sha
graftTree' subtree graftloc basetree repo hdl = go basetree subdirs graftdirs 
  where
	go tsha (subdir:restsubdirs) (topmostgraphdir:restgraphdirs) = do
		Tree t <- getTree LsTree.LsTreeNonRecursive tsha repo
		let abovegraftpoint i = gitPath i == gitPath subdir
		t' <- case partition abovegraftpoint t of
			-- the graft point is not already in the tree,
			-- so graft it in, keeping the existing tree
			-- content
			([], _) -> do
				graft <- graftin (topmostgraphdir:restgraphdirs)
				return (graft:t)
			(matching, rest) -> do
				newshas <- forM matching $ \case
					RecordedSubTree tloc tsha' _
						| null restgraphdirs -> return $
							RecordedSubTree tloc subtree []
						| otherwise -> do
							tsha'' <- go tsha' restsubdirs restgraphdirs
							return $ RecordedSubTree tloc tsha'' []
					_ -> graftin (topmostgraphdir:restgraphdirs)
				return (newshas ++ rest)
		mkTree hdl t'
	go _ _ [] = return subtree
	go _ [] _ = return subtree
	
	graftin t = recordSubTree hdl $ graftin' t
	graftin' [] = RecordedSubTree graftloc subtree []
	graftin' (d:rest) 
		| d == graftloc = graftin' []
		| otherwise = NewSubTree d [graftin' rest]

	subdirs = P.splitDirectories $ gitPath graftloc

	-- For a graftloc of "foo/bar/baz", this generates
	-- ["foo", "foo/bar", "foo/bar/baz"]
	graftdirs = map (asTopFilePath . toInternalGitPath) $
		mkpaths [] subdirs
	mkpaths _ [] = []
	mkpaths base (d:rest) = (P.joinPath base P.</> d) : mkpaths (base ++ [d]) rest

{- Assumes the list is ordered, with tree objects coming right before their
 - contents. -}
extractTree :: [LsTree.TreeItem] -> Either String Tree
extractTree l = case go [] inTopTree l of
	Right (t, []) -> Right (Tree t)
	Right _ -> parseerr "unexpected tree form"
	Left e -> parseerr e
  where
	go t _ [] = Right (t, [])
	go t intree (i:is)
		| intree i = case readObjectType (LsTree.typeobj i) of
			Just BlobObject ->
				let b = TreeBlob (LsTree.file i) (LsTree.mode i) (LsTree.sha i)
				in go (b:t) intree is
			Just TreeObject -> case go [] (beneathSubTree i) is of
				Right (subtree, is') ->
					let st = RecordedSubTree (LsTree.file i) (LsTree.sha i) subtree
					in go (st:t) intree is'
				Left e -> Left e
			Just CommitObject ->
				let c = TreeCommit (LsTree.file i) (LsTree.mode i) (LsTree.sha i)
				in go (c:t) intree is
			_ -> parseerr ("unexpected object type \"" ++ decodeBS (LsTree.typeobj i) ++ "\"")
		| otherwise = Right (t, i:is)
	parseerr = Left

class GitPath t where
	gitPath :: t -> RawFilePath

instance GitPath RawFilePath where
	gitPath = id

instance GitPath FilePath where
	gitPath = toRawFilePath

instance GitPath TopFilePath where
	gitPath = getTopFilePath

instance GitPath TreeItem where
	gitPath (TreeItem f _ _) = gitPath f

instance GitPath LsTree.TreeItem where
	gitPath = gitPath . LsTree.file

instance GitPath TreeContent where
	gitPath (TreeBlob f _ _) = gitPath f
	gitPath (RecordedSubTree f _ _) = gitPath f
	gitPath (NewSubTree f _) = gitPath f
	gitPath (TreeCommit f _ _) = gitPath f

inTopTree :: GitPath t => t -> Bool
inTopTree = inTree "."

inTree :: (GitPath t, GitPath f) => t -> f -> Bool
inTree t f = gitPath t == P.takeDirectory (gitPath f)

beneathSubTree :: (GitPath t, GitPath f) => t -> f -> Bool
beneathSubTree t f = prefix `B.isPrefixOf` P.normalise (gitPath f)
  where
	tp = gitPath t
	prefix = if B.null tp then tp else P.addTrailingPathSeparator (P.normalise tp)