Improve TreeWalker algorithm.

src/bsv/path_map.py

@@ -0,0 +1,58 @@
+# bsv - Backup, Synchronization, Versioning
+# Copyright (C) 2023  Simon Boyé
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+from __future__ import annotations
+from dataclasses import dataclass
+from itertools import pairwise
+
+from pathlib import Path, PurePosixPath
+from typing import Any
+
+
+@dataclass(order=True, frozen=True, slots=True)
+class PathPair:
+    bsv: PurePosixPath
+    fs: Path
+
+    def __post_init__(self):
+        if not self.bsv.is_absolute() or not self.fs.is_absolute():
+            raise ValueError("paths in path_map must be absolute")
+
+    @classmethod
+    def from_obj(cls, obj: dict[str, str]) -> PathPair:
+        return cls(
+            bsv = PurePosixPath(obj["bsv"]),
+            fs = Path(obj["fs"]),
+        )
+
+
+class PathMap:
+    paths: list[PathPair]
+
+    def __init__(self, paths: list[PathPair]=[]):
+        self.paths = sorted(paths)
+        for path0, path1 in pairwise(self.paths):
+            if path0 == path1 or path1.bsv.relative_to(path0.bsv):
+                raise ValueError("bsv paths must be unique and independent")
+
+    @classmethod
+    def from_obj(cls, obj: list[dict[str, str]]) -> PathMap:
+        return cls([
+            PathPair.from_obj(item)
+            for item in obj
+        ])
+
+    def clone(self) -> PathMap:
+        return PathMap(self.paths)

src/bsv/repository.py

@@ -19,19 +19,23 @@ from dataclasses import dataclass
 from datetime import datetime as DateTime
 import hashlib
 from io import BytesIO
-from pathlib import Path, PurePosixPath
+from pathlib import Path
 import platform
 import tomllib
-from typing import Any, BinaryIO, Callable, Type
+from typing import TYPE_CHECKING, BinaryIO, Callable, Type
 
 from fastcdc import fastcdc
 import tomlkit
 
 from bsv import __version__
 from bsv.exception import ConfigError
+from bsv.path_map import PathMap
 from bsv.simple_cas import SimpleCas
 from bsv.simple_cas.cas import Digest, SimpleCas
-from bsv.util import Hash, read_exact, read_exact_or_eof, time_from_timestamp, timestamp_from_time
+from bsv.util import Hash, read_exact, read_exact_or_eof, time_from_timestamp_us, timestamp_us_from_time
+
+if TYPE_CHECKING:
+    from bsv.tree_walker import TreeWalker
 
 
 DEFAULT_MIN_CHUNK_SIZE = 1 << 12
@@ -48,7 +52,7 @@ class Repository:
     _avg_chunk_size: int = DEFAULT_AVG_CHUNK_SIZE
     _max_chunk_size: int = DEFAULT_MAX_CHUNK_SIZE
 
-    _path_map: list[PathPair]
+    _path_map: PathMap
     # _remotes: list[object]
 
     _context_depth: int = 0
@@ -72,10 +76,7 @@ class Repository:
         self._avg_chunk_size = bsv.get("avg_chunk_size")
         self._max_chunk_size = bsv.get("max_chunk_size")
 
-        self._path_map = [
-            PathPair.from_obj(pair)
-            for pair in bsv.get("path_map", [])
-        ]
+        self._path_map = PathMap.from_obj(bsv.get("path_map", []))
 
     @property
     def path(self) -> Path:
@@ -90,14 +91,14 @@ class Repository:
         return self._name
 
     @property
-    def path_map(self) -> list[PathPair]:
-        return list(self._path_map)
+    def path_map(self) -> PathMap:
+        return self._path_map.clone()
 
     def get_blob(self, digest: Digest) -> Blob:
         with self:
             return self._read(digest, object_type=b"blob", cls=Blob) # type: ignore
 
-    def add_blob(self, stream: BinaryIO, dry_run: bool=False) -> Digest:
+    def add_blob(self, stream: BinaryIO, *, dry_run: bool=False) -> Digest:
         with self:
             return self._write(b"blob", stream, dry_run=dry_run)
 
@@ -105,11 +106,11 @@ class Repository:
         with self:
             return Tree.from_bytes(self, self._cas.read(digest, object_type=b"tree").data)
 
-    def add_tree(self, tree: Tree, dry_run: bool=False) -> Digest:
+    def add_tree(self, tree: Tree, *, dry_run: bool=False) -> Digest:
         with self:
             return self._cas.write(b"tree", tree.to_bytes(), dry_run=dry_run)
 
-    def add_tree_from_path(self, path: Path, dry_run: bool=False) -> Digest:
+    def add_tree_from_path(self, path: Path, *, dry_run: bool=False) -> Digest:
         from bsv.tree_walker import TreeWalker
         walker = TreeWalker(self, dry_run=dry_run)
         return walker.add_tree(path)
@@ -118,16 +119,44 @@ class Repository:
         with self:
             return Snapshot.from_bytes(self, self._cas.read(digest, object_type=b"snap").data)
 
-    def add_snapshot(self, snapshot: Snapshot, dry_run: bool=False) -> Digest:
+    def add_snapshot(self, snapshot: Snapshot, *, dry_run: bool=False) -> Digest:
         with self:
             return self._cas.write(b"snap", snapshot.to_bytes(), dry_run=dry_run)
 
+    # def take_snapshot(
+    #     self,
+    #     parent_digests: list[Digest] = [],
+    #     *,
+    #     walker_type: Type[TreeWalker] | None = None,
+    #     dry_run: bool = False,
+    # ):
+    #     from bsv.tree_walker import TreeWalker
+
+    #     walker = (walker_type or TreeWalker)(self, dry_run=dry_run)
+
+    #     # parents = [
+    #     #     self.get_snapshot(digest)
+    #     #     for digest in parent_digests
+    #     # ]
+    #     parent = self.get_snapshot(parent_digests[0]) if parent_digests else None
+
+    #     snapshot = Snapshot(
+    #         repo = self,
+    #         tree_digest = walker.add_virtual_tree(self._path_map, parent=),
+    #         parents = parent_digests,
+    #         repo_name = self._name,
+    #         timestamp = timestamp_us_from_time(DateTime.now()),
+    #     )
+    #     return self.add_snapshot(snapshot, dry_run=dry_run)
+
+
+
     def _read(self, digest: Digest, object_type: bytes, cls: Type[ChunkedObject]) -> ChunkedObject:
         obj = self._cas.read(digest, object_type=object_type)
         stream = BytesIO(obj.data)
         return cls.from_stream(self, stream, digest_size=self._cas._digest_size)
 
-    def _write(self, object_type: bytes, stream: BinaryIO, dry_run: bool=False) -> Digest:
+    def _write(self, object_type: bytes, stream: BinaryIO, *, dry_run: bool=False) -> Digest:
         out = BytesIO()
         size = 0
         for chunk in fastcdc(
@@ -332,7 +361,7 @@ class TreeItem:
     object_type: bytes
     size: int
     permissions: int
-    modification_timestamp: int
+    modification_timestamp_us: int
     name: str
 
     def __init__(
@@ -341,7 +370,7 @@ class TreeItem:
         object_type: bytes,
         size: int,
         permissions: int,
-        modification_timestamp: int,
+        modification_timestamp_us: int,
         name: str,
     ):
         if "/\\" in name:
@@ -350,15 +379,15 @@ class TreeItem:
         self.object_type = object_type
         self.size = size
         self.permissions = permissions
-        self.modification_timestamp = modification_timestamp
+        self.modification_timestamp_us = modification_timestamp_us
         self.name = name
 
     @property
     def modification_time(self) -> DateTime:
-        return time_from_timestamp(self.modification_timestamp)
+        return time_from_timestamp_us(self.modification_timestamp_us)
     @modification_time.setter
     def modification_time(self, time: DateTime):
-        self.modification_timestamp = timestamp_from_time(time)
+        self.modification_timestamp_us = timestamp_us_from_time(time)
 
     @classmethod
     def from_stream(cls, stream: BinaryIO, digest_size: int) -> TreeItem | None:
@@ -370,7 +399,7 @@ class TreeItem:
             object_type = read_exact(stream, 4),
             size = int.from_bytes(read_exact(stream, 8)),
             permissions = int.from_bytes(read_exact(stream, 2)),
-            modification_timestamp = int.from_bytes(read_exact(stream, 8), signed=True),
+            modification_timestamp_us = int.from_bytes(read_exact(stream, 8), signed=True),
             name = read_exact(stream, int.from_bytes(read_exact(stream, 2))).decode("utf-8"),
         )
 
@@ -379,7 +408,7 @@ class TreeItem:
         stream.write(self.object_type)
         stream.write(self.size.to_bytes(8))
         stream.write(self.permissions.to_bytes(2))
-        stream.write(self.modification_timestamp.to_bytes(8, signed=True))
+        stream.write(self.modification_timestamp_us.to_bytes(8, signed=True))
         name_bytes = self.name.encode("utf-8")
         stream.write(len(name_bytes).to_bytes(2))
         stream.write(name_bytes)
@@ -391,23 +420,31 @@ class TreeItem:
 class Snapshot:
     repo: Repository
     tree_digest: Digest
+    parents: list[Digest]
     repo_name: str
-    timestamp: int
+    timestamp_us: int
+
+    def __post_init__(self):
+        assert len(self.parents) < 256
 
     @property
     def time(self) -> DateTime:
-        return time_from_timestamp(self.timestamp)
+        return time_from_timestamp_us(self.timestamp_us)
     @time.setter
     def time(self, time: DateTime):
-        self.timestamp = timestamp_from_time(time)
+        self.timestamp_us = timestamp_us_from_time(time)
 
     @classmethod
     def from_stream(cls, repo: Repository, stream: BinaryIO) -> Snapshot:
         return Snapshot(
             repo = repo,
             tree_digest = Digest(read_exact(stream, repo._cas._digest_size)),
+            parents = [
+                Digest(read_exact(stream, repo._cas._digest_size))
+                for _ in range(int.from_bytes(read_exact(stream, 1)))
+            ],
             repo_name = read_exact(stream, int.from_bytes(read_exact(stream, 2))).decode("utf-8"),
-            timestamp = int.from_bytes(read_exact(stream, 8), signed=True),
+            timestamp_us = int.from_bytes(read_exact(stream, 8), signed=True),
         )
 
     @classmethod
@@ -416,40 +453,17 @@ class Snapshot:
         return cls.from_stream(repo, stream)
 
     def write(self, stream: BinaryIO):
+        assert len(self.parents) < 256
         stream.write(self.tree_digest.digest)
+        stream.write(len(self.parents).to_bytes(1))
+        for parent in self.parents:
+            stream.write(parent.digest)
         repo_name_bytes = self.repo_name.encode("utf-8")
         stream.write(len(repo_name_bytes).to_bytes(2))
         stream.write(repo_name_bytes)
-        stream.write(self.timestamp.to_bytes(8, signed=True))
+        stream.write(self.timestamp_us.to_bytes(8, signed=True))
 
     def to_bytes(self) -> bytes:
         stream = BytesIO()
         self.write(stream)
         return stream.getvalue()
-
-
-
-
-class PathPair:
-    bsv: PurePosixPath
-    fs: Path
-
-    def __init__(self, bsv: PurePosixPath, fs: Path):
-        self.bsv = bsv
-        self.fs = fs
-
-    @classmethod
-    def from_obj(cls, obj: dict[str, Any]) -> PathPair:
-        bsv = PurePosixPath(obj["bsv"])
-        fs = Path(obj["fs"])
-
-        if not bsv.is_absolute() or not fs.is_absolute():
-            raise ValueError("paths in path_map must be absolute")
-
-        return cls(
-            bsv = obj["bsv"],
-            fs = obj["fs"],
-        )
-
-    def __lt__(self, rhs: PathPair) -> bool:
-        return self.bsv < rhs.bsv

src/bsv/tree_walker.py

@@ -15,12 +15,14 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 from __future__ import annotations
 
+from datetime import datetime as DateTime, timedelta as TimeDelta
 from enum import Enum
 from os import stat_result
 from pathlib import Path
 import stat
 
 from bsv.object import Digest
+from bsv.path_map import PathMap
 from bsv.repository import Repository, Tree, TreeItem
 from bsv.util import is_bsv_repository, object_type_from_mode
 
@@ -28,9 +30,20 @@ from bsv.util import is_bsv_repository, object_type_from_mode
 class Action(Enum):
     ADD = "add"
     UPDATE = "update"
+    REMOVE = "remove"
     IGNORE = "ignore"
     ERROR = "error"
 
+    @classmethod
+    def from_digests(cls, digest: Digest, source_digest: Digest | None) -> tuple[Action, IgnoreCause | None]:
+        assert digest
+        if not source_digest:
+            return Action.ADD, None
+        elif source_digest == digest:
+            return Action.IGNORE, IgnoreCause.UNCHANGED
+        else:
+            return Action.UPDATE, None
+
 class IgnoreCause(Enum):
     IGNORE_RULE = "ignore_rule"
     UNCHANGED = "unchanged"
@@ -39,88 +52,177 @@ class IgnoreCause(Enum):
 
 class TreeWalker:
     _repo: Repository
+    _time_rounding_us: int = 2000000
+    _force_hash: bool = False
     _dry_run: bool = False
 
-    def __init__(self, repo: Repository, dry_run: bool=False):
+    def __init__(
+        self,
+        repo: Repository,
+        *,
+        time_rounding_us: int = 2000000,
+        force_hash: bool = False,
+        dry_run: bool = False,
+    ):
         self._repo = repo
+        self._time_rounding_us = time_rounding_us
+        self._force_hash = force_hash
         self._dry_run = dry_run
 
-    def add_tree(self, path: Path) -> Digest:
+    # def add_virtual_tree(self, paths: PathMap) -> Digest:
+    #     root = {}
+    #     for pair in paths.paths:
+    #         vdir = root
+    #         for part in pair.bsv.parts[:-1]:
+    #             vdir = vdir.setdefault(part, {})
+    #         vdir[pair.bsv.parts[-1]] = pair.fs
+
+    #     return self._add_virtual_tree(root)
+
+    # def _add_virtual_tree(self, vtree: dict[str, dict | Path]) -> Digest:
+    #     tree = Tree(self._repo, [])
+    #     for name, value in vtree.items():
+    #         if isinstance(value, dict):
+    #             digest = self._add_virtual_tree(value)
+    #         elif isinstance(value, Path):
+    #             digest = self.add_tree(value)
+    #         else:
+    #             raise TypeError(f"unexpected type {type(vtree).__name__} for vtree")
+    #         tree.items.append(TreeItem(
+    #             digest = digest,
+    #             object_type = b"tree",
+    #             size = 0,
+    #             permissions = 0o766,
+    #             modification_timestamp = timestamp_us_from_time(DateTime.now()),
+    #             name = name,
+    #         ))
+    #     return self._repo.add_tree(tree, dry_run=self._dry_run)
+
+    def add_tree(self, path: Path, *, source_digest: Digest | None=None) -> Digest:
         pstat = path.stat(follow_symlinks=False)
         if self.ignore(path, pstat):
             self.report(Action.IGNORE, path, pstat, IgnoreCause.IGNORE_RULE)
             return Digest()
-        return self._add_tree(path, pstat)
+        return self._add_tree(path, pstat, source_digest=source_digest)
+
+    def _add_tree(self, path: Path, pstat: stat_result, *, source_digest: Digest | None) -> Digest:
+        source = self._repo.get_tree(source_digest) if source_digest else None
 
-    def _add_tree(self, path: Path, pstat: stat_result) -> Digest:
         tree = Tree(self._repo, [])
-        for item in sorted(path.iterdir()):
-            digest = Digest()
-            try:
-                istat = item.lstat()
-                if self.ignore(item, istat):
-                    self.report(Action.IGNORE, item, istat, IgnoreCause.IGNORE_RULE)
-                    continue
-                object_type = object_type_from_mode(istat.st_mode)
-                if object_type == b"slnk":
-                    digest = self._add_symlink(item, istat)
-                elif object_type == b"tree":
-                    digest = self._add_tree(item, istat)
-                elif object_type == b"blob":
-                    digest = self._add_blob(item, istat)
-                else:
-                    self.report(Action.IGNORE, item, istat, IgnoreCause.UNSUPPORTED_TYPE)
+        subpaths = sorted(path.iterdir())
+
+        subpath_index = 0
+        source_item_index = 0
+
+        while subpath_index < len(subpaths) or (source and source_item_index < len(source.items)):
+            subpath = subpaths[subpath_index] if subpath_index < len(subpaths) else None
+            source_item = source.items[source_item_index] if source and source_item_index < len(source.items) else None
+
+            if subpath and source_item:
+                if subpath.name < source_item.name:
+                    source_item = None
+                elif subpath.name > source_item.name:
+                    subpath = None
+
+            if subpath is not None:
+                subpath_index += 1
+            if source_item is not None:
+                source_item_index += 1
+
+            if subpath is not None:
+                digest = Digest()
+                try:
+                    istat = subpath.lstat()
+
+                    if self.ignore(subpath, istat, source=source_item):
+                        self.report(Action.IGNORE, subpath, istat, IgnoreCause.IGNORE_RULE)
+                        continue
+
+                    if (source_item is not None and
+                        not self._force_hash and
+                        not stat.S_ISDIR(istat.st_mode) and
+                        pstat.st_size == source_item.size and
+                        pstat.st_mtime_ns // (1000 * self._time_rounding_us) == source_item.modification_timestamp_us // self._time_rounding_us
+                    ):
+                        self.report(Action.IGNORE, subpath, istat, IgnoreCause.UNCHANGED)
+                        tree.items.append(source_item)
+                        continue
+
+                    sub_source_digest = source_item and source_item.digest
+                    object_type = object_type_from_mode(istat.st_mode)
+                    if object_type == b"slnk":
+                        digest = self._add_symlink(subpath, istat, source_digest=sub_source_digest)
+                    elif object_type == b"tree":
+                        digest = self._add_tree(subpath, istat, source_digest=sub_source_digest)
+                    elif object_type == b"blob":
+                        digest = self._add_blob(subpath, istat, source_digest=sub_source_digest)
+                    else:
+                        self.report(Action.IGNORE, subpath, istat, IgnoreCause.UNSUPPORTED_TYPE)
+                        continue
+                except Exception as err:
+                    self.report(Action.ERROR, subpath, None, err)
                     continue
-            except Exception as err:
-                self.report(Action.ERROR, item, None, err)
-                continue
 
-            if digest:
-                self.report(Action.ADD, path, pstat)
-                tree.items.append(TreeItem(
-                    digest = digest,
-                    object_type = object_type,
-                    size = istat.st_size,
-                    permissions = stat.S_IMODE(istat.st_mode),
-                    modification_timestamp = istat.st_mtime_ns,
-                    name = item.name,
-                ))
+                if digest:
+                    tree.items.append(TreeItem(
+                        digest = digest,
+                        object_type = object_type,
+                        size = istat.st_size,
+                        permissions = stat.S_IMODE(istat.st_mode),
+                        modification_timestamp_us = istat.st_mtime_ns // 1000,
+                        name = subpath.name,
+                    ))
+            elif source_item:
+                self.report(Action.REMOVE, path / source_item.name, None, source_item)
 
-        return self._repo.add_tree(tree, dry_run=self._dry_run)
+        digest = self._repo.add_tree(tree, dry_run=self._dry_run)
 
+        action, info = Action.from_digests(digest, source_digest)
+        self.report(action, path, pstat, info)
+        return digest
 
-    def _add_symlink(self, path: Path, pstat: stat_result) -> Digest:
+
+    def _add_symlink(self, path: Path, pstat: stat_result, *, source_digest: Digest | None) -> Digest:
         # TODO: Store symlink relative to current dir ?
         #   * What about symlink that points outside of the backup dirs
         #   * Should symlinks that points inside the backup dirs but in another
         #     mount-point adjusted ?
         #   * Should absolute symlink be restored as absolute ?
-        self.report(Action.ADD, path, pstat)
-        return self._repo._cas.write(
+        digest = self._repo._cas.write(
             b"slnk",
             path.readlink().as_posix().encode("utf-8"),
             dry_run = self._dry_run,
         )
 
-    def _add_blob(self, path: Path, pstat: stat_result) -> Digest:
-        self.report(Action.ADD, path, pstat)
+        action, info = Action.from_digests(digest, source_digest)
+        self.report(action, path, pstat, info)
+        return digest
+
+    def _add_blob(self, path: Path, pstat: stat_result, *, source_digest: Digest | None) -> Digest:
         with path.open("rb") as stream:
-            return self._repo.add_blob(stream, dry_run=self._dry_run)
+            digest = self._repo.add_blob(stream, dry_run=self._dry_run)
 
+        action, info = Action.from_digests(digest, source_digest)
+        self.report(action, path, pstat, info)
+        return digest
 
-    def ignore(self, path: Path, pstat: stat_result) -> bool:
+
+    def ignore(self, path: Path, pstat: stat_result, *, source: TreeItem | None=None) -> bool:
         return is_bsv_repository(path)
 
-    def report(self, action: Action, path: Path, pstat: stat_result | None, info: IgnoreCause | Exception | None=None):
+    def report(self, action: Action, path: Path, pstat: stat_result | None, info: IgnoreCause | Exception | TreeItem | None=None):
         match action, info:
             case (Action.ADD, None):
                 print(f"Add: {path}")
+            case (Action.UPDATE, None):
+                print(f"Add: {path}")
+            case (Action.REMOVE, item) if isinstance(item, TreeItem):
+                print(f"Remove: {path / item.name}")
             case (Action.IGNORE, IgnoreCause.IGNORE_RULE):
                 print(f"Ignore (rule): {path}")
             case (Action.IGNORE, IgnoreCause.UNCHANGED):
                 print(f"Ignore (unchanged): {path}")
             case (Action.IGNORE, IgnoreCause.UNSUPPORTED_TYPE) if pstat is not None:
-                assert pstat is not None
                 print(f"Ignore (unsupported type {path_type_name(pstat)}): {path}")
             case (Action.ERROR, _) if isinstance(info, Exception):
                 print(f"Error {info}: {path}")

src/bsv/util.py

@@ -25,10 +25,10 @@ from typing import BinaryIO
 EPOCH = DateTime(1970, 1, 1, tzinfo=UTC)
 
 
-def time_from_timestamp(timestamp: int) -> DateTime:
+def time_from_timestamp_us(timestamp: int) -> DateTime:
     return EPOCH + TimeDelta(microseconds=timestamp)
 
-def timestamp_from_time(time: DateTime) -> int:
+def timestamp_us_from_time(time: DateTime) -> int:
     return (time.astimezone(UTC) - EPOCH) // TimeDelta(microseconds=1)
 
 

tests/test_repository.py

@@ -18,12 +18,13 @@ from datetime import UTC, datetime
 from os import stat_result
 from pathlib import Path
 from random import randbytes
+from shutil import rmtree
 from typing import Iterator
 
 import pytest
 from tempfile import TemporaryDirectory
 
-from bsv.repository import Repository, Snapshot, Tree, TreeItem, create_repository, timestamp_from_time
+from bsv.repository import Repository, Snapshot, Tree, TreeItem, create_repository, timestamp_us_from_time
 from bsv.simple_cas.cas import Digest
 from bsv.tree_walker import Action, IgnoreCause, TreeWalker
 
@@ -66,7 +67,7 @@ def test_read_write_tree(repo: Repository):
                 object_type = b"blob",
                 size = 123,
                 permissions = 0o744,
-                modification_timestamp = timestamp_from_time(now),
+                modification_timestamp_us = timestamp_us_from_time(now),
                 name = "xyz",
             ),
             TreeItem(
@@ -74,7 +75,7 @@ def test_read_write_tree(repo: Repository):
                 object_type = b"slnk",
                 size = 42,
                 permissions = 0o777,
-                modification_timestamp = timestamp_from_time(now),
+                modification_timestamp_us = timestamp_us_from_time(now),
                 name = "foobar",
             ),
         ]
@@ -90,8 +91,12 @@ def test_read_write_snapshot(repo: Repository):
     snapshot = Snapshot(
         repo = repo,
         tree_digest = Digest(bytes([42]) * repo._cas._digest_size),
+        parents = [
+            Digest(bytes([123]) * repo._cas._digest_size),
+            Digest(bytes([124]) * repo._cas._digest_size),
+        ],
         repo_name = "test_repo",
-        timestamp = timestamp_from_time(datetime.now()),
+        timestamp_us = timestamp_us_from_time(datetime.now()),
     )
 
     assert Snapshot.from_bytes(repo, snapshot.to_bytes()) == snapshot
@@ -104,7 +109,7 @@ class TestTreeWalker(TreeWalker):
     reports: list
 
     def __init__(self, repo: Repository, dry_run: bool=False):
-        super().__init__(repo, dry_run)
+        super().__init__(repo, dry_run=dry_run)
         self.reports = []
 
     def report(
@@ -115,12 +120,12 @@ class TestTreeWalker(TreeWalker):
         info: IgnoreCause | Exception | None = None
     ):
         super().report(action, path, pstat, info)
-        self.reports.append((action, path, pstat, info))
+        self.reports.append((action, path, info if action != Action.REMOVE else None))
 
 
 def test_add_tree(tmp_dir: Path, repo: Repository):
-    dir = tmp_dir / "test"
-    structure = {
+    dir = tmp_dir / "test0"
+    structure0 = {
         "folder": {
             "sub_folder": {
                 "empty_folder": {},
@@ -134,11 +139,28 @@ def test_add_tree(tmp_dir: Path, repo: Repository):
             "bsv_config.toml": b"[bsv]\n",
         },
     }
+    structure1 = {
+        "folder": {
+            "sub_folder": {
+                "empty_folder": {},
+                "foo.txt": b"Hello World!\n",
+            },
+            "bar.dat": bytes(range(256)) * 2,
+        },
+        "new_file": b"whatever",
+        "Another test with long name and spaces and a bang !": b"Should works.\n",
+        "bsv_repo": {
+            "bsv_config.toml": b"[bsv]\n",
+        },
+    }
 
-    create_file_structure(dir, structure)
+    expected0 = dict(structure0)
+    del expected0["bsv_repo"]
 
-    walker = TestTreeWalker(repo)
-    dir_digest = walker.add_tree(dir)
+    expected1 = dict(structure1)
+    del expected1["bsv_repo"]
+
+    create_file_structure(dir, structure0)
 
     def check(digest: Digest, value: dict | bytes):
         if isinstance(value, dict):
@@ -152,19 +174,79 @@ def test_add_tree(tmp_dir: Path, repo: Repository):
             data = blob.reader().read()
             assert data == value
 
-    expected = dict(structure)
-    del expected["bsv_repo"]
-    check(dir_digest, expected)
+    walker = TestTreeWalker(repo)
+    dir_digest0 = walker.add_tree(dir)
+    assert walker.reports == [
+        (Action.ADD, dir / "Another test with long name and spaces and a bang !", None),
+        (Action.IGNORE, dir / "bsv_repo", IgnoreCause.IGNORE_RULE),
+        (Action.ADD, dir / "folder/bar.dat", None),
+        (Action.ADD, dir / "folder/sub_folder/empty_folder", None),
+        (Action.ADD, dir / "folder/sub_folder/foo.txt", None),
+        (Action.ADD, dir / "folder/sub_folder", None),
+        (Action.ADD, dir / "folder/test.py", None),
+        (Action.ADD, dir / "folder", None),
+        (Action.ADD, dir, None),
+    ]
+    check(dir_digest0, expected0)
+
+    create_file_structure(dir, structure1)
+
+    walker.reports.clear()
+    dir_digest1 = walker.add_tree(dir, source_digest=dir_digest0)
+    assert walker.reports == [
+        (Action.IGNORE, dir / "Another test with long name and spaces and a bang !", IgnoreCause.UNCHANGED),
+        (Action.IGNORE, dir / "bsv_repo", IgnoreCause.IGNORE_RULE),
+        (Action.UPDATE, dir / "folder/bar.dat", None),
+        (Action.IGNORE, dir / "folder/sub_folder/empty_folder", IgnoreCause.UNCHANGED),
+        (Action.IGNORE, dir / "folder/sub_folder/foo.txt", IgnoreCause.UNCHANGED),
+        (Action.IGNORE, dir / "folder/sub_folder", IgnoreCause.UNCHANGED),
+        (Action.REMOVE, dir / "folder/test.py", None),
+        (Action.UPDATE, dir / "folder", None),
+        (Action.ADD, dir / "new_file", None),
+        (Action.UPDATE, dir, None),
+    ]
+    check(dir_digest1, expected1)
 
 
 def create_file_structure(dst: Path, value: dict | bytes):
-    assert not dst.exists()
-    if isinstance(value, dict):
-        dst.mkdir()
-        for name, item in value.items():
-            create_file_structure(dst / name, item)
-    elif isinstance(value, bytes):
-        dst.write_bytes(value)
+    if isinstance(value, bytes):
+        if dst.is_dir():
+            rmtree(str(dst))
+        if not dst.is_file() or dst.read_bytes() != value:
+            dst.write_bytes(value)
+    elif isinstance(value, dict):
+        if dst.is_file():
+            dst.unlink()
+        if not dst.is_dir():
+            dst.mkdir()
+
+        items = sorted(value.items())
+        fs_paths = sorted(dst.iterdir())
+
+        item_index = 0
+        fs_path_index = 0
+
+        while item_index < len(value) or fs_path_index < len(fs_paths):
+            name, subitem = items[item_index] if item_index < len(items) else (None, None)
+            fs_path = fs_paths[fs_path_index] if fs_path_index < len(fs_paths) else None
+
+            if name and fs_path:
+                if name < fs_path.name:
+                    fs_path = None
+                elif name > fs_path.name:
+                    name = None
+
+            if name:
+                item_index += 1
+            if fs_path:
+                fs_path_index += 1
+
+            if name:
+                create_file_structure(dst / name, subitem) # type: ignore
+            elif fs_path and fs_path.is_dir():
+                rmtree(fs_path)
+            elif fs_path:
+                fs_path.unlink()
     else:
         raise TypeError(f"invalid type {type(value).__name__} for parameter value")