{-# LANGUAGE ScopedTypeVariables, MultiParamTypeClasses, FlexibleInstances #-} -- | The abstract representation of a Tree and useful abstract utilities to -- handle those. module Storage.Hashed.Tree ( Tree, Blob(..), TreeItem(..), ItemType(..), Hash(..) , makeTree, makeTreeWithHash, emptyTree, emptyBlob, makeBlob, makeBlobBS -- * Unfolding stubbed (lazy) Trees. -- -- | By default, Tree obtained by a read function is stubbed: it will -- contain Stub items that need to be executed in order to access the -- respective subtrees. 'expand' will produce an unstubbed Tree. , expandUpdate, expand, expandPath -- * Tree access and lookup. , items, list, listImmediate, treeHash , lookup, find, findFile, findTree, itemHash, itemType , zipCommonFiles, zipFiles, zipTrees, diffTrees -- * Files (Blobs). , readBlob -- * Filtering trees. , FilterTree(..), restrict -- * Manipulating trees. , modifyTree, updateTree, updateSubtrees, overlay ) where import Prelude hiding( lookup, filter, all ) import Storage.Hashed.AnchoredPath import Storage.Hashed.Hash import qualified Data.ByteString.Lazy.Char8 as BL import qualified Data.ByteString.Char8 as BS import qualified Data.Map as M import Data.Maybe( catMaybes, isNothing ) import Data.List( union, sort ) import Control.Applicative( (<$>) ) -------------------------------- -- Tree, Blob and friends -- data Blob m = Blob !(m BL.ByteString) !Hash data TreeItem m = File !(Blob m) | SubTree !(Tree m) | Stub !(m (Tree m)) !Hash data ItemType = BlobType | TreeType deriving (Show, Eq) -- | Abstraction of a filesystem tree. -- Please note that the Tree returned by the respective read operations will -- have TreeStub items in it. To obtain a Tree without such stubs, call -- expand on it, eg.: -- -- > tree <- readDarcsPristine "." >>= expand -- -- When a Tree is expanded, it becomes \"final\". All stubs are forced and the -- Tree can be traversed purely. Access to actual file contents stays in IO -- though. -- -- A Tree may have a Hash associated with it. A pair of Tree's is identical -- whenever their hashes are (the reverse need not hold, since not all Trees -- come equipped with a hash). data Tree m = Tree { items :: (M.Map Name (TreeItem m)) -- | Get hash of a Tree. This is guaranteed to uniquely -- identify the Tree (including any blob content), as far as -- cryptographic hashes are concerned. Sha256 is recommended. , treeHash :: !Hash } listImmediate :: Tree m -> [(Name, TreeItem m)] listImmediate = M.toList . items -- | Get a hash of a TreeItem. May be Nothing. itemHash :: TreeItem m -> Hash itemHash (File (Blob _ h)) = h itemHash (SubTree t) = treeHash t itemHash (Stub _ h) = h itemType :: TreeItem m -> ItemType itemType (File _) = BlobType itemType (SubTree _) = TreeType itemType (Stub _ _) = TreeType emptyTree :: (Monad m) => Tree m emptyTree = Tree { items = M.empty , treeHash = NoHash } emptyBlob :: (Monad m) => Blob m emptyBlob = Blob (return BL.empty) NoHash makeBlob :: (Monad m) => BL.ByteString -> Blob m makeBlob str = Blob (return str) (sha256 str) makeBlobBS :: (Monad m) => BS.ByteString -> Blob m makeBlobBS s' = let s = BL.fromChunks [s'] in Blob (return s) (sha256 s) makeTree :: (Monad m) => [(Name,TreeItem m)] -> Tree m makeTree l = Tree { items = M.fromList l , treeHash = NoHash } makeTreeWithHash :: (Monad m) => [(Name,TreeItem m)] -> Hash -> Tree m makeTreeWithHash l h = Tree { items = M.fromList l , treeHash = h } ----------------------------------- -- Tree access and lookup -- -- | Look up a 'Tree' item (an immediate subtree or blob). lookup :: Tree m -> Name -> Maybe (TreeItem m) lookup t n = M.lookup n (items t) find' :: TreeItem m -> AnchoredPath -> Maybe (TreeItem m) find' t (AnchoredPath []) = Just t find' (SubTree t) (AnchoredPath (d : rest)) = case lookup t d of Just sub -> find' sub (AnchoredPath rest) Nothing -> Nothing find' _ _ = Nothing -- | Find a 'TreeItem' by its path. Gives 'Nothing' if the path is invalid. find :: Tree m -> AnchoredPath -> Maybe (TreeItem m) find = find' . SubTree -- | Find a 'Blob' by its path. Gives 'Nothing' if the path is invalid, or does -- not point to a Blob. findFile :: Tree m -> AnchoredPath -> Maybe (Blob m) findFile t p = case find t p of Just (File x) -> Just x _ -> Nothing -- | Find a 'Tree' by its path. Gives 'Nothing' if the path is invalid, or does -- not point to a Tree. findTree :: Tree m -> AnchoredPath -> Maybe (Tree m) findTree t p = case find t p of Just (SubTree x) -> Just x _ -> Nothing -- | List all contents of a 'Tree'. list :: Tree m -> [(AnchoredPath, TreeItem m)] list t_ = paths t_ (AnchoredPath []) where paths t p = [ (appendPath p n, i) | (n,i) <- listImmediate t ] ++ concat [ paths subt (appendPath p subn) | (subn, SubTree subt) <- listImmediate t ] expandUpdate :: (Monad m) => (AnchoredPath -> Tree m -> m (Tree m)) -> Tree m -> m (Tree m) expandUpdate update t_ = go (AnchoredPath []) t_ where go path t = do let subtree (name, sub) = do tree <- go (path `appendPath` name) =<< unstub sub return (name, SubTree tree) expanded <- mapM subtree [ x | x@(_, item) <- listImmediate t, isSub item ] let orig = [ i | i <- listImmediate t, not $ isSub $ snd i ] orig_map = M.filter (not . isSub) (items t) expanded_map = M.fromList expanded tree = t { items = M.union orig_map expanded_map } update path tree -- | Expand a stubbed Tree into a one with no stubs in it. You might want to -- filter the tree before expanding to save IO. This is the basic -- implementation, which may be overriden by some Tree instances (this is -- especially true of the Index case). expand :: (Monad m) => Tree m -> m (Tree m) expand = expandUpdate $ \_ -> return -- | Unfold a path in a (stubbed) Tree, such that the leaf node of the path is -- reachable without crossing any stubs. Moreover, the leaf ought not be a Stub -- in the resulting Tree. A non-existent path is expanded as far as it can be. expandPath :: (Monad m) => Tree m -> AnchoredPath -> m (Tree m) expandPath t_ path_ = expand' t_ path_ where expand' t (AnchoredPath []) = return t expand' t (AnchoredPath (n:rest)) = case lookup t n of (Just item) | isSub item -> amend t n rest =<< unstub item _ -> return t -- fail $ "Descent error in expandPath: " ++ show path_ amend t name rest sub = do sub' <- expand' sub (AnchoredPath rest) let tree = t { items = M.insert name (SubTree sub') (items t) } return tree class (Monad m) => FilterTree a m where -- | Given @pred tree@, produce a 'Tree' that only has items for which -- @pred@ returns @True@. -- The tree might contain stubs. When expanded, these will be subject to -- filtering as well. filter :: (AnchoredPath -> TreeItem m -> Bool) -> a m -> a m instance (Monad m) => FilterTree Tree m where filter predicate t_ = filter' t_ (AnchoredPath []) where filter' t path = let subs = (catMaybes [ (,) name `fmap` wibble path name item | (name,item) <- listImmediate t ]) in t { items = M.mapMaybeWithKey (wibble path) $ items t } wibble path name item = let npath = path `appendPath` name in if predicate npath item then Just $ filterSub npath item else Nothing filterSub npath (SubTree t) = SubTree $ filter' t npath filterSub npath (Stub stub h) = Stub (do x <- stub return $ filter' x npath) h filterSub _ x = x -- | Given two Trees, a @guide@ and a @tree@, produces a new Tree that is a -- identical to @tree@, but only has those items that are present in both -- @tree@ and @guide@. The @guide@ Tree may not contain any stubs. restrict :: (FilterTree t m, Monad n) => Tree n -> t m -> t m restrict guide tree = filter accept tree where accept path item = case (find guide path, item) of (Just (SubTree _), SubTree _) -> True (Just (SubTree _), Stub _ _) -> True (Just (File _), File _) -> True (Just (Stub _ _), _) -> error "*sulk* Go away, you, you precondition violator!" (_, _) -> False -- | Read a Blob into a Lazy ByteString. Might be backed by an mmap, use with -- care. readBlob :: Blob m -> m BL.ByteString readBlob (Blob r _) = r -- | For every pair of corresponding blobs from the two supplied trees, -- evaluate the supplied function and accumulate the results in a list. Hint: -- to get IO actions through, just use sequence on the resulting list. -- NB. This won't expand any stubs. zipCommonFiles :: (AnchoredPath -> Blob m -> Blob m -> a) -> Tree m -> Tree m -> [a] zipCommonFiles f a b = catMaybes [ flip (f p) x `fmap` findFile a p | (p, File x) <- list b ] -- | For each file in each of the two supplied trees, evaluate the supplied -- function (supplying the corresponding file from the other tree, or Nothing) -- and accumulate the results in a list. Hint: to get IO actions through, just -- use sequence on the resulting list. NB. This won't expand any stubs. zipFiles :: (AnchoredPath -> Maybe (Blob m) -> Maybe (Blob m) -> a) -> Tree m -> Tree m -> [a] zipFiles f a b = [ f p (findFile a p) (findFile b p) | p <- paths a `sortedUnion` paths b ] where paths t = sort [ p | (p, File _) <- list t ] zipTrees :: (AnchoredPath -> Maybe (TreeItem m) -> Maybe (TreeItem m) -> a) -> Tree m -> Tree m -> [a] zipTrees f a b = [ f p (find a p) (find b p) | p <- reverse (paths a `sortedUnion` paths b) ] where paths t = sort [ p | (p, _) <- list t ] -- | Helper function for taking the union of AnchoredPath lists that -- are already sorted. This function does not check the precondition -- so use it carefully. sortedUnion :: [AnchoredPath] -> [AnchoredPath] -> [AnchoredPath] sortedUnion [] ys = ys sortedUnion xs [] = xs sortedUnion a@(x:xs) b@(y:ys) = case compare x y of LT -> x : sortedUnion xs b EQ -> x : sortedUnion xs ys GT -> y : sortedUnion a ys -- | Cautiously extracts differing subtrees from a pair of Trees. It will never -- do any unneccessary expanding. Tree hashes are used to cut the comparison as -- high up the Tree branches as possible. The result is a pair of trees that do -- not share any identical subtrees. They are derived from the first and second -- parameters respectively and they are always fully expanded. It might be -- advantageous to feed the result into 'zipFiles' or 'zipTrees'. diffTrees :: forall m. (Functor m, Monad m) => Tree m -> Tree m -> m (Tree m, Tree m) diffTrees left right = if treeHash left `match` treeHash right then return (emptyTree, emptyTree) else diff left right where isFile (File _) = True isFile _ = False notFile = not . isFile isEmpty = null . listImmediate subtree :: TreeItem m -> m (Tree m) subtree (Stub x _) = x subtree (SubTree x) = return x subtree (File _) = error "diffTrees tried to descend a File as a subtree" maybeUnfold (Stub x _) = SubTree `fmap` (x >>= expand) maybeUnfold (SubTree x) = SubTree `fmap` expand x maybeUnfold i = return i immediateN t = [ n | (n, _) <- listImmediate t ] diff left' right' = do is <- sequence [ case (lookup left' n, lookup right' n) of (Just l, Nothing) -> do l' <- maybeUnfold l return (n, Just l', Nothing) (Nothing, Just r) -> do r' <- maybeUnfold r return (n, Nothing, Just r') (Just l, Just r) | itemHash l `match` itemHash r -> return (n, Nothing, Nothing) | notFile l && notFile r -> do x <- subtree l y <- subtree r (x', y') <- diffTrees x y if isEmpty x' && isEmpty y' then return (n, Nothing, Nothing) else return (n, Just $ SubTree x', Just $ SubTree y') | isFile l && isFile r -> return (n, Just l, Just r) | otherwise -> do l' <- maybeUnfold l r' <- maybeUnfold r return (n, Just l', Just r') _ -> error "n lookups failed" | n <- immediateN left' `union` immediateN right' ] let is_l = [ (n, l) | (n, Just l, _) <- is ] is_r = [ (n, r) | (n, _, Just r) <- is ] return (makeTree is_l, makeTree is_r) -- | Modify a Tree (by replacing, or removing or adding items). modifyTree :: (Monad m) => Tree m -> AnchoredPath -> Maybe (TreeItem m) -> Tree m modifyTree t_ p_ i_ = snd $ go t_ p_ i_ where fix t unmod items' = (unmod, t { items = countmap items' `seq` items' , treeHash = if unmod then treeHash t else NoHash }) go t (AnchoredPath []) (Just (SubTree sub)) = (treeHash t `match` treeHash sub, sub) go t (AnchoredPath [n]) (Just item) = fix t unmod items' where !items' = M.insert n item (items t) !unmod = itemHash item `match` case lookup t n of Nothing -> NoHash Just i -> itemHash i go t (AnchoredPath [n]) Nothing = fix t unmod items' where !items' = M.delete n (items t) !unmod = isNothing $ lookup t n go t path@(AnchoredPath (n:r)) item = fix t unmod items' where subtree s = go s (AnchoredPath r) item !items' = M.insert n sub (items t) !sub = snd sub' !unmod = fst sub' !sub' = case lookup t n of Just (SubTree s) -> let (mod, sub) = subtree s in (mod, SubTree sub) Just (Stub s _) -> (False, Stub (do x <- s return $! snd $! subtree x) NoHash) Nothing -> (False, SubTree $! snd $! subtree emptyTree) _ -> error $ "Modify tree at " ++ show path go _ (AnchoredPath []) (Just (Stub _ _)) = error "Bug in descent in modifyTree." go _ (AnchoredPath []) (Just (File _)) = error "Bug in descent in modifyTree." go _ (AnchoredPath []) Nothing = error "Bug in descent in modifyTree." countmap = M.fold (\_ i -> i + 1) 0 updateSubtrees :: (Tree m -> Tree m) -> Tree m -> Tree m updateSubtrees fun t = fun $ t { items = M.mapWithKey (curry $ snd . update) $ items t , treeHash = NoHash } where update (k, SubTree s) = (k, SubTree $ updateSubtrees fun s) update (k, File f) = (k, File f) update (_, Stub _ _) = error "Stubs not supported in updateTreePostorder" -- | Does /not/ expand the tree. updateTree :: (Functor m, Monad m) => (TreeItem m -> m (TreeItem m)) -> Tree m -> m (Tree m) updateTree fun t = do immediate <- mapM update $ listImmediate t SubTree t' <- fun . SubTree $ t { items = M.fromList immediate , treeHash = NoHash } return t' where update (k, SubTree tree) = (\new -> (k, SubTree new)) <$> updateTree fun tree update (k, item) = (\new -> (k, new)) <$> fun item -- | Lay one tree over another. The resulting Tree will look like the base (1st -- parameter) Tree, although any items also present in the overlay Tree will be -- taken from the overlay. It is not allowed to overlay a different kind of an -- object, nor it is allowed for the overlay to add new objects to base. This -- means that the overlay Tree should be a subset of the base Tree (although -- any extraneous items will be ignored by the implementation). overlay :: (Functor m, Monad m) => Tree m -> Tree m -> Tree m overlay base over = Tree { items = M.fromList immediate , treeHash = NoHash } where immediate = [ (n, get n) | (n, _) <- listImmediate base ] get n = case (M.lookup n $ items base, M.lookup n $ items over) of (Just (File _), Just f@(File _)) -> f (Just (SubTree b), Just (SubTree o)) -> SubTree $ overlay b o (Just (Stub b _), Just (SubTree o)) -> Stub (flip overlay o `fmap` b) NoHash (Just (SubTree b), Just (Stub o _)) -> Stub (overlay b `fmap` o) NoHash (Just (Stub b _), Just (Stub o _)) -> Stub (do o' <- o b' <- b return $ overlay b' o') NoHash (Just x, _) -> x (_, _) -> error $ "Unexpected case in overlay at get " ++ show n ++ "." ------ Private utilities shared among multiple functions. -------- unstub :: (Monad m) => TreeItem m -> m (Tree m) unstub (Stub s _) = s unstub (SubTree s) = return s isSub :: TreeItem m -> Bool isSub (File _) = False isSub _ = True