From: Jakob <jakob@jcornell.net>
Date: Fri, 6 Dec 2019 20:03:58 +0000 (-0600)
Subject: Tweak ADS API, implement new-style metadata preference
X-Git-Url: https://jcornell.net/gitweb/gitweb.cgi?a=commitdiff_plain;h=c0962d3ea41d02d7ac68d8e8cdb31f15ea5e213c;p=bb-sync-api.git

Tweak ADS API, implement new-style metadata preference
---

diff --git a/fs.py b/fs.py
index 58ea4de..f2357f0 100644
--- a/fs.py
+++ b/fs.py
@@ -14,12 +14,13 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 from collections import namedtuple
+from enum import Enum
 import json
 import pathlib
 import re
 
 
-class WinPath(pathlib.WindowsPath):
+def get_ads(path: pathlib.WindowsPath, name):
 	r"""
 	This constructs a path for an NTFS alternate data stream on Windows.
 	In most cases, for directories, a trailing slash is permitted and optional:
@@ -36,13 +37,17 @@ class WinPath(pathlib.WindowsPath):
 	we need to manually add a separator to ensure the resulting path actually
 	points to an ADS. This makes the path absolute, but that's okay because there
 	doesn't seem to be any way to get an ADS on a relative path with a drive.
+
+	Incidentally, this is essentially cross-platform, since there are Linux NTFS
+	implementations with ADS support using the same path syntax. But if the
+	application were targeting other platforms there would probably be platform-
+	specific implementations of this function.
 	"""
-	def get_ads(self, name):
-		full_name = self.name + ':' + name
-		if self.name:
-			return self.with_name(full_name)
-		else:
-			return self.joinpath('/', full_name)
+	full_name = path.name + ':' + name
+	if path.name:
+		return path.with_name(full_name)
+	else:
+		return path.joinpath('/', full_name)
 
 
 def clean_win_path(seg):
@@ -73,8 +78,16 @@ def content_path(course_path, segments):
 BB_META_STREAM_NAME = '8f3b98ea-e227-478f-bb58-5c31db476409'
 
 
-VersionInfo = namedtuple('ParseResult', ['bb_id', 'version'])
-VersionInfo.next = lambda self: VersionInfo(self.bb_id, self.version + 1)
+VersionInfo = namedtuple('ParseResult', ['meta_type', 'bb_id', 'version'])
+VersionInfo.MetaType = Enum('MetaType', ['OLD', 'NEW'])
+
+def _vinfo_next(self):
+	return VersionInfo(
+		self.MetaType.NEW,
+		self.bb_id,
+		self.version + 1,
+	)
+VersionInfo.next = _vinfo_next
 
 
 def _extract_version(path):
@@ -82,7 +95,7 @@ def _extract_version(path):
 		return None
 
 	info = None
-	stream_path = WinPath(path).get_ads(BB_META_STREAM_NAME)
+	stream_path = fs.get_ads(path, BB_META_STREAM_NAME)
 	if stream_path.exists():
 		# NTFS ADS metadata
 		with stream_path.open() as f:
@@ -95,7 +108,7 @@ def _extract_version(path):
 				version = metadata.get('version')
 				version_typecheck = lambda v: isinstance(v, int) if path.is_file() else v is None
 				if isinstance(bb_id, str) and version_typecheck(version):
-					info = VersionInfo(bb_id, version)
+					info = VersionInfo(VersionInfo.MetaType.NEW, bb_id, version)
 	else:
 		# old in-filename metadata
 		(stem, _) = _split_name(path.name)
@@ -103,7 +116,7 @@ def _extract_version(path):
 		if match:
 			version = int(match.group('version')) if match.group('version') else None
 			if (version is None) == path.is_dir():
-				info = VersionInfo(match.group('id'), version)
+				info = VersionInfo(VersionInfo.MetaType.OLD, match.group('id'), version)
 
 	return info
 
@@ -129,6 +142,15 @@ def join_content_path(path, content_doc):
 	ver_map = get_child_versions(path)
 	versions = [v for v in ver_map if v.bb_id == content_doc['id']]
 	if versions:
+		if len(versions) > 1:
+			# attempt to disambiguate by preferring directories with new-style metadata
+			versions = [
+				info for info in versions
+				if info.meta_type is VersionInfo.MetaType.NEW
+			]
+
+		# Either destructure could fail based on filesystem contents,
+		# but neither failure is likely to happen by accident.
 		[info] = versions
 		[child_path] = ver_map[info]
 		return child_path
@@ -137,7 +159,11 @@ def join_content_path(path, content_doc):
 		new_path.mkdir(exist_ok = True)
 		write_metadata(
 			new_path,
-			VersionInfo(bb_id = content_doc['id'], version = None),
+			VersionInfo(
+				VersionInfo.MetaType.NEW,
+				bb_id = content_doc['id'],
+				version = None
+			),
 		)
 		return new_path
 
@@ -163,5 +189,5 @@ def get_new_path(parent, base_name):
 
 
 def write_metadata(path, version_info):
-	with WinPath(path).get_ads(BB_META_STREAM_NAME).open('x') as f:
+	with fs.get_ads(path, BB_META_STREAM_NAME).open('x') as f:
 		json.dump({'contentId': version_info.bb_id, 'version': version_info.version}, f)
diff --git a/main.py b/main.py
index e2d78db..eafa2b8 100644
--- a/main.py
+++ b/main.py
@@ -84,7 +84,7 @@ with StorageManager(Path('auth_cache')) as storage_mgr:
 	[course_id] = course_ids
 	[content_id] = content_ids
 
-	local_course_root = fs.WinPath(cfg_section['base_path'])
+	local_course_root = Path(cfg_section['base_path'])
 	local_course_root.mkdir(parents = True, exist_ok = True)
 	meta_path = local_course_root.get_ads(fs.BB_META_STREAM_NAME)
 	if meta_path.is_file():
@@ -142,7 +142,8 @@ with StorageManager(Path('auth_cache')) as storage_mgr:
 
 				my_versions = [info for info in versions.keys() if info.bb_id == att_id]
 				if my_versions:
-					latest = max(my_versions, key = attrgetter('version'))
+					sort_key = lambda v: (v.version, v.meta_type is v.MetaType.NEW)
+					latest = max(my_versions, key = sort_key)
 					latest_paths = versions[latest]
 					if len(latest_paths) == 1:
 						[latest_path] = latest_paths