diff --git a/lib/bloc/list_album.dart b/lib/bloc/list_album.dart
index e2385bc1..fbd143af 100644
--- a/lib/bloc/list_album.dart
+++ b/lib/bloc/list_album.dart
@@ -3,6 +3,7 @@ import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/event/event.dart';
 import 'package:nc_photos/use_case/list_album.dart';
 
diff --git a/lib/bloc/ls_dir.dart b/lib/bloc/ls_dir.dart
index 139076d2..ece5c474 100644
--- a/lib/bloc/ls_dir.dart
+++ b/lib/bloc/ls_dir.dart
@@ -4,6 +4,7 @@ import 'package:bloc/bloc.dart';
 import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/iterable_extension.dart';
 import 'package:nc_photos/use_case/ls.dart';
 
diff --git a/lib/bloc/scan_dir.dart b/lib/bloc/scan_dir.dart
index 143601de..fced334d 100644
--- a/lib/bloc/scan_dir.dart
+++ b/lib/bloc/scan_dir.dart
@@ -7,6 +7,7 @@ import 'package:kiwi/kiwi.dart';
 import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/event/event.dart';
 import 'package:nc_photos/iterable_extension.dart';
 import 'package:nc_photos/use_case/scan_dir.dart';
diff --git a/lib/entity/album.dart b/lib/entity/album.dart
index 784f1a29..b016dfc1 100644
--- a/lib/entity/album.dart
+++ b/lib/entity/album.dart
@@ -10,6 +10,7 @@ import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/app_db.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/exception.dart';
 import 'package:nc_photos/int_util.dart' as int_util;
 import 'package:nc_photos/iterable_extension.dart';
diff --git a/lib/entity/file.dart b/lib/entity/file.dart
index 31ffe380..9e3d4ff0 100644
--- a/lib/entity/file.dart
+++ b/lib/entity/file.dart
@@ -1,26 +1,12 @@
-import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:equatable/equatable.dart';
 import 'package:flutter/foundation.dart';
-import 'package:idb_sqflite/idb_sqflite.dart';
 import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
-import 'package:nc_photos/api/api.dart';
-import 'package:nc_photos/app_db.dart';
 import 'package:nc_photos/entity/exif.dart';
-import 'package:nc_photos/entity/webdav_response_parser.dart';
-import 'package:nc_photos/exception.dart';
-import 'package:nc_photos/int_util.dart' as int_util;
-import 'package:nc_photos/iterable_extension.dart';
 import 'package:nc_photos/or_null.dart';
-import 'package:nc_photos/remote_storage_util.dart' as remote_storage_util;
 import 'package:nc_photos/string_extension.dart';
-import 'package:nc_photos/touch_token_manager.dart';
-import 'package:path/path.dart' as path;
-import 'package:quiver/iterables.dart';
-import 'package:uuid/uuid.dart';
-import 'package:xml/xml.dart';
 
 int compareFileDateTimeDescending(File x, File y) {
   final xDate = x.metadata?.exif?.dateTimeOriginal ?? x.lastModified;
@@ -459,582 +445,3 @@ abstract class FileDataSource {
   /// remote.php/dav/files/admin/new/dir
   Future<void> createDir(Account account, String path);
 }
-
-class FileWebdavDataSource implements FileDataSource {
-  @override
-  list(
-    Account account,
-    File f, {
-    int depth,
-  }) async {
-    _log.fine("[list] ${f.path}");
-    final response = await Api(account).files().propfind(
-      path: f.path,
-      depth: depth,
-      getlastmodified: 1,
-      resourcetype: 1,
-      getetag: 1,
-      getcontenttype: 1,
-      getcontentlength: 1,
-      hasPreview: 1,
-      fileid: 1,
-      customNamespaces: {
-        "com.nkming.nc_photos": "app",
-      },
-      customProperties: [
-        "app:metadata",
-      ],
-    );
-    if (!response.isGood) {
-      _log.severe("[list] Failed requesting server: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-
-    final xml = XmlDocument.parse(response.body);
-    final files = WebdavFileParser()(xml);
-    // _log.fine("[list] Parsed files: [$files]");
-    return files.map((e) {
-      if (e.metadata == null || e.metadata.fileEtag == e.etag) {
-        return e;
-      } else {
-        _log.info("[list] Ignore outdated metadata for ${e.path}");
-        return e.copyWith(metadata: OrNull(null));
-      }
-    }).toList();
-  }
-
-  @override
-  remove(Account account, File f) async {
-    _log.info("[remove] ${f.path}");
-    final response = await Api(account).files().delete(path: f.path);
-    if (!response.isGood) {
-      _log.severe("[remove] Failed requesting server: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-  }
-
-  @override
-  getBinary(Account account, File f) async {
-    _log.info("[getBinary] ${f.path}");
-    final response = await Api(account).files().get(path: f.path);
-    if (!response.isGood) {
-      _log.severe("[getBinary] Failed requesting server: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-    return response.body;
-  }
-
-  @override
-  putBinary(Account account, String path, Uint8List content) async {
-    _log.info("[putBinary] $path");
-    final response =
-        await Api(account).files().put(path: path, content: content);
-    if (!response.isGood) {
-      _log.severe("[putBinary] Failed requesting server: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-  }
-
-  @override
-  updateMetadata(Account account, File f, Metadata metadata) async {
-    _log.info("[updateMetadata] ${f.path}");
-    if (metadata != null && metadata.fileEtag != f.etag) {
-      _log.warning(
-          "[updateMetadata] etag mismatch (metadata: ${metadata.fileEtag}, file: ${f.etag})");
-    }
-    final setProps = {
-      if (metadata != null) "app:metadata": jsonEncode(metadata.toJson()),
-    };
-    final removeProps = [
-      if (metadata == null) "app:metadata",
-    ];
-    final response = await Api(account).files().proppatch(
-          path: f.path,
-          namespaces: {
-            "com.nkming.nc_photos": "app",
-          },
-          set: setProps.isNotEmpty ? setProps : null,
-          remove: removeProps.isNotEmpty ? removeProps : null,
-        );
-    if (!response.isGood) {
-      _log.severe("[updateMetadata] Failed requesting server: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-  }
-
-  @override
-  copy(
-    Account account,
-    File f,
-    String destination, {
-    bool shouldOverwrite,
-  }) async {
-    _log.info("[copy] ${f.path} to $destination");
-    final response = await Api(account).files().copy(
-          path: f.path,
-          destinationUrl: "${account.url}/$destination",
-          overwrite: shouldOverwrite,
-        );
-    if (!response.isGood) {
-      _log.severe("[copy] Failed requesting sever: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-  }
-
-  @override
-  move(
-    Account account,
-    File f,
-    String destination, {
-    bool shouldOverwrite,
-  }) async {
-    _log.info("[move] ${f.path} to $destination");
-    final response = await Api(account).files().move(
-          path: f.path,
-          destinationUrl: "${account.url}/$destination",
-          overwrite: shouldOverwrite,
-        );
-    if (!response.isGood) {
-      _log.severe("[move] Failed requesting sever: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-  }
-
-  @override
-  createDir(Account account, String path) async {
-    _log.info("[createDir] $path");
-    final response = await Api(account).files().mkcol(
-          path: path,
-        );
-    if (!response.isGood) {
-      _log.severe("[createDir] Failed requesting sever: $response");
-      throw ApiException(
-          response: response,
-          message: "Failed communicating with server: ${response.statusCode}");
-    }
-  }
-
-  static final _log = Logger("entity.file.FileWebdavDataSource");
-}
-
-class FileAppDbDataSource implements FileDataSource {
-  @override
-  list(Account account, File f) {
-    _log.info("[list] ${f.path}");
-    return AppDb.use((db) async {
-      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.fileStoreName);
-      return await _doList(store, account, f);
-    });
-  }
-
-  @override
-  remove(Account account, File f) {
-    _log.info("[remove] ${f.path}");
-    return AppDb.use((db) async {
-      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.fileStoreName);
-      final index = store.index(AppDbFileEntry.indexName);
-      final path = AppDbFileEntry.toPath(account, f);
-      final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
-      final keys = await index
-          .openKeyCursor(range: range, autoAdvance: true)
-          .map((cursor) => cursor.primaryKey)
-          .toList();
-      for (final k in keys) {
-        _log.fine("[remove] Removing DB entry: $k");
-        await store.delete(k);
-      }
-    });
-  }
-
-  @override
-  getBinary(Account account, File f) {
-    _log.info("[getBinary] ${f.path}");
-    throw UnimplementedError();
-  }
-
-  @override
-  putBinary(Account account, String path, Uint8List content) async {
-    _log.info("[putBinary] $path");
-    // do nothing, we currently don't store file contents locally
-  }
-
-  @override
-  updateMetadata(Account account, File f, Metadata metadata) {
-    _log.info("[updateMetadata] ${f.path}");
-    return AppDb.use((db) async {
-      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.fileStoreName);
-      final parentDir = File(path: path.dirname(f.path));
-      final parentList = await _doList(store, account, parentDir);
-      final jsonList = parentList.map((e) {
-        if (e.path == f.path) {
-          return e.copyWith(metadata: OrNull(metadata));
-        } else {
-          return e;
-        }
-      });
-      await _cacheListResults(store, account, parentDir, jsonList);
-    });
-  }
-
-  @override
-  copy(
-    Account account,
-    File f,
-    String destination, {
-    bool shouldOverwrite,
-  }) async {
-    // do nothing
-  }
-
-  @override
-  move(
-    Account account,
-    File f,
-    String destination, {
-    bool shouldOverwrite,
-  }) async {
-    // do nothing
-  }
-
-  @override
-  createDir(Account account, String path) async {
-    // do nothing
-  }
-
-  Future<List<File>> _doList(ObjectStore store, Account account, File f) async {
-    final index = store.index(AppDbFileEntry.indexName);
-    final path = AppDbFileEntry.toPath(account, f);
-    final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
-    final List results = await index.getAll(range);
-    if (results?.isNotEmpty == true) {
-      final entries = results
-          .map((e) => AppDbFileEntry.fromJson(e.cast<String, dynamic>()));
-      return entries.map((e) {
-        _log.info("[_doList] ${e.path}[${e.index}]");
-        return e.data;
-      }).reduce((value, element) => value + element);
-    } else {
-      throw CacheNotFoundException("No entry: $path");
-    }
-  }
-
-  static final _log = Logger("entity.file.FileAppDbDataSource");
-}
-
-class FileCachedDataSource implements FileDataSource {
-  FileCachedDataSource({
-    this.shouldCheckCache = false,
-  });
-
-  @override
-  list(Account account, File f) async {
-    final cacheManager = _CacheManager(
-      appDbSrc: _appDbSrc,
-      remoteSrc: _remoteSrc,
-      shouldCheckCache: shouldCheckCache,
-    );
-    final cache = await cacheManager.list(account, f);
-    if (cacheManager.isGood) {
-      return cache;
-    }
-
-    // no cache or outdated
-    try {
-      final remote = await _remoteSrc.list(account, f);
-      await _cacheResult(account, f, remote);
-      if (shouldCheckCache) {
-        // update our local touch token to match the remote one
-        final tokenManager = TouchTokenManager();
-        try {
-          await tokenManager.setLocalToken(
-              account, f, cacheManager.remoteTouchToken);
-        } catch (e, stacktrace) {
-          _log.shout("[list] Failed while setLocalToken", e, stacktrace);
-          // ignore error
-        }
-      }
-
-      if (cache != null) {
-        try {
-          await _cleanUpCachedDir(account, remote, cache);
-        } catch (e, stacktrace) {
-          _log.shout("[list] Failed while _cleanUpCachedList", e, stacktrace);
-          // ignore error
-        }
-      }
-      return remote;
-    } on ApiException catch (e) {
-      if (e.response.statusCode == 404) {
-        _log.info("[list] File removed: $f");
-        _appDbSrc.remove(account, f);
-        return [];
-      } else {
-        rethrow;
-      }
-    }
-  }
-
-  @override
-  remove(Account account, File f) async {
-    await _appDbSrc.remove(account, f);
-    await _remoteSrc.remove(account, f);
-  }
-
-  @override
-  getBinary(Account account, File f) {
-    return _remoteSrc.getBinary(account, f);
-  }
-
-  @override
-  putBinary(Account account, String path, Uint8List content) async {
-    await _remoteSrc.putBinary(account, path, content);
-  }
-
-  @override
-  updateMetadata(Account account, File f, Metadata metadata) async {
-    await _remoteSrc
-        .updateMetadata(account, f, metadata)
-        .then((_) => _appDbSrc.updateMetadata(account, f, metadata));
-
-    // generate a new random token
-    final token = Uuid().v4().replaceAll("-", "");
-    final tokenManager = TouchTokenManager();
-    final dir = File(path: path.dirname(f.path));
-    await tokenManager.setLocalToken(account, dir, token);
-    final fileRepo = FileRepo(this);
-    await tokenManager.setRemoteToken(fileRepo, account, dir, token);
-    _log.info(
-        "[updateMetadata] New touch token '$token' for dir '${dir.path}'");
-  }
-
-  @override
-  copy(
-    Account account,
-    File f,
-    String destination, {
-    bool shouldOverwrite,
-  }) async {
-    await _remoteSrc.copy(account, f, destination,
-        shouldOverwrite: shouldOverwrite);
-  }
-
-  @override
-  move(
-    Account account,
-    File f,
-    String destination, {
-    bool shouldOverwrite,
-  }) async {
-    await _remoteSrc.move(account, f, destination,
-        shouldOverwrite: shouldOverwrite);
-  }
-
-  @override
-  createDir(Account account, String path) async {
-    await _remoteSrc.createDir(account, path);
-  }
-
-  Future<void> _cacheResult(Account account, File f, List<File> result) {
-    return AppDb.use((db) async {
-      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.fileStoreName);
-      await _cacheListResults(store, account, f, result);
-    });
-  }
-
-  /// Remove dangling dir entries in the file object store
-  Future<void> _cleanUpCachedDir(
-      Account account, List<File> remoteResults, List<File> cachedResults) {
-    final removed = cachedResults
-        .where((cache) =>
-            !remoteResults.any((remote) => remote.path == cache.path))
-        .toList();
-    if (removed.isEmpty) {
-      return Future.delayed(Duration.zero);
-    }
-    return AppDb.use((db) async {
-      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.fileStoreName);
-      final index = store.index(AppDbFileEntry.indexName);
-      for (final r in removed) {
-        final path = AppDbFileEntry.toPath(account, r);
-        final keys = [];
-        // delete the dir itself
-        final dirRange = KeyRange.bound([path, 0], [path, int_util.int32Max]);
-        // delete with KeyRange is not supported in idb_shim/idb_sqflite
-        // await store.delete(dirRange);
-        keys.addAll(await index
-            .openKeyCursor(range: dirRange, autoAdvance: true)
-            .map((cursor) => cursor.primaryKey)
-            .toList());
-        // then its children
-        final childrenRange =
-            KeyRange.bound(["$path/", 0], ["$path/\uffff", int_util.int32Max]);
-        keys.addAll(await index
-            .openKeyCursor(range: childrenRange, autoAdvance: true)
-            .map((cursor) => cursor.primaryKey)
-            .toList());
-
-        for (final k in keys) {
-          _log.fine("[_cleanUpCachedDir] Removing DB entry: $k");
-          await store.delete(k);
-        }
-      }
-    });
-  }
-
-  final bool shouldCheckCache;
-
-  final _remoteSrc = FileWebdavDataSource();
-  final _appDbSrc = FileAppDbDataSource();
-
-  static final _log = Logger("entity.file.FileCachedDataSource");
-}
-
-class _CacheManager {
-  _CacheManager({
-    @required this.appDbSrc,
-    @required this.remoteSrc,
-    this.shouldCheckCache = false,
-  });
-
-  /// Return the cached results of listing a directory [f]
-  ///
-  /// Should check [isGood] before using the cache returning by this method
-  Future<List<File>> list(Account account, File f) async {
-    final trimmedRootPath = f.path.trimAny("/");
-    List<File> cache;
-    try {
-      cache = await appDbSrc.list(account, f);
-      // compare the cached root
-      final cacheEtag = cache
-          .firstWhere((element) => element.path.trimAny("/") == trimmedRootPath)
-          .etag;
-      if (cacheEtag != null) {
-        // compare the etag to see if the content has been updated
-        var remoteEtag = f.etag;
-        if (remoteEtag == null) {
-          // no etag supplied, we need to query it form remote
-          final remote = await remoteSrc.list(account, f, depth: 0);
-          assert(remote.length == 1);
-          remoteEtag = remote.first.etag;
-        }
-        if (cacheEtag == remoteEtag) {
-          _log.fine(
-              "[_listCache] etag matched for ${AppDbFileEntry.toPath(account, f)}");
-          if (shouldCheckCache) {
-            await _checkTouchToken(account, f, cache);
-          } else {
-            _isGood = true;
-          }
-        }
-      } else {
-        _log.info(
-            "[_list] Remote content updated for ${AppDbFileEntry.toPath(account, f)}");
-      }
-    } on CacheNotFoundException catch (_) {
-      // normal when there's no cache
-    } catch (e, stacktrace) {
-      _log.shout("[_list] Cache failure", e, stacktrace);
-    }
-    return cache;
-  }
-
-  bool get isGood => _isGood;
-  String get remoteTouchToken => _remoteToken;
-
-  Future<void> _checkTouchToken(
-      Account account, File f, List<File> cache) async {
-    final touchPath =
-        "${remote_storage_util.getRemoteTouchDir(account)}/${f.strippedPath}";
-    final fileRepo = FileRepo(FileCachedDataSource());
-    final tokenManager = TouchTokenManager();
-    String remoteToken;
-    try {
-      remoteToken = await tokenManager.getRemoteToken(fileRepo, account, f);
-    } catch (e, stacktrace) {
-      _log.shout(
-          "[_checkTouchToken] Failed getting remote token at '$touchPath'",
-          e,
-          stacktrace);
-    }
-    _remoteToken = remoteToken;
-
-    String localToken;
-    try {
-      localToken = await tokenManager.getLocalToken(account, f);
-    } catch (e, stacktrace) {
-      _log.shout(
-          "[_checkTouchToken] Failed getting local token at '$touchPath'",
-          e,
-          stacktrace);
-    }
-
-    if (localToken != remoteToken) {
-      _log.info(
-          "[_checkTouchToken] Remote and local token differ, cache outdated");
-    } else {
-      _isGood = true;
-    }
-  }
-
-  final FileWebdavDataSource remoteSrc;
-  final FileAppDbDataSource appDbSrc;
-  final bool shouldCheckCache;
-
-  var _isGood = false;
-  String _remoteToken;
-
-  static final _log = Logger("entity.file._CacheManager");
-}
-
-Future<void> _cacheListResults(
-    ObjectStore store, Account account, File f, Iterable<File> results) async {
-  final index = store.index(AppDbFileEntry.indexName);
-  final path = AppDbFileEntry.toPath(account, f);
-  final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
-  // count number of entries for this dir
-  final count = await index.count(range);
-  int newCount = 0;
-  for (final pair
-      in partition(results, AppDbFileEntry.maxDataSize).withIndex()) {
-    _log.info(
-        "[_cacheListResults] Caching $path[${pair.item1}], length: ${pair.item2.length}");
-    await store.put(
-      AppDbFileEntry(path, pair.item1, pair.item2).toJson(),
-      AppDbFileEntry.toPrimaryKey(account, f, pair.item1),
-    );
-    ++newCount;
-  }
-  if (count > newCount) {
-    // index is 0-based
-    final rmRange = KeyRange.bound([path, newCount], [path, int_util.int32Max]);
-    final rmKeys = await index
-        .openKeyCursor(range: rmRange, autoAdvance: true)
-        .map((cursor) => cursor.primaryKey)
-        .toList();
-    for (final k in rmKeys) {
-      _log.fine("[_cacheListResults] Removing DB entry: $k");
-      await store.delete(k);
-    }
-  }
-}
-
-final _log = Logger("entity.file");
diff --git a/lib/entity/file/data_source.dart b/lib/entity/file/data_source.dart
new file mode 100644
index 00000000..b9de38c4
--- /dev/null
+++ b/lib/entity/file/data_source.dart
@@ -0,0 +1,601 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:flutter/foundation.dart';
+import 'package:idb_shim/idb_client.dart';
+import 'package:logging/logging.dart';
+import 'package:nc_photos/account.dart';
+import 'package:nc_photos/api/api.dart';
+import 'package:nc_photos/app_db.dart';
+import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/webdav_response_parser.dart';
+import 'package:nc_photos/exception.dart';
+import 'package:nc_photos/int_util.dart' as int_util;
+import 'package:nc_photos/iterable_extension.dart';
+import 'package:nc_photos/or_null.dart';
+import 'package:nc_photos/remote_storage_util.dart' as remote_storage_util;
+import 'package:nc_photos/string_extension.dart';
+import 'package:nc_photos/touch_token_manager.dart';
+import 'package:path/path.dart' as path;
+import 'package:quiver/iterables.dart';
+import 'package:uuid/uuid.dart';
+import 'package:xml/xml.dart';
+
+class FileWebdavDataSource implements FileDataSource {
+  @override
+  list(
+    Account account,
+    File f, {
+    int depth,
+  }) async {
+    _log.fine("[list] ${f.path}");
+    final response = await Api(account).files().propfind(
+      path: f.path,
+      depth: depth,
+      getlastmodified: 1,
+      resourcetype: 1,
+      getetag: 1,
+      getcontenttype: 1,
+      getcontentlength: 1,
+      hasPreview: 1,
+      fileid: 1,
+      customNamespaces: {
+        "com.nkming.nc_photos": "app",
+      },
+      customProperties: [
+        "app:metadata",
+      ],
+    );
+    if (!response.isGood) {
+      _log.severe("[list] Failed requesting server: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+
+    final xml = XmlDocument.parse(response.body);
+    final files = WebdavFileParser()(xml);
+    // _log.fine("[list] Parsed files: [$files]");
+    return files.map((e) {
+      if (e.metadata == null || e.metadata.fileEtag == e.etag) {
+        return e;
+      } else {
+        _log.info("[list] Ignore outdated metadata for ${e.path}");
+        return e.copyWith(metadata: OrNull(null));
+      }
+    }).toList();
+  }
+
+  @override
+  remove(Account account, File f) async {
+    _log.info("[remove] ${f.path}");
+    final response = await Api(account).files().delete(path: f.path);
+    if (!response.isGood) {
+      _log.severe("[remove] Failed requesting server: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+  }
+
+  @override
+  getBinary(Account account, File f) async {
+    _log.info("[getBinary] ${f.path}");
+    final response = await Api(account).files().get(path: f.path);
+    if (!response.isGood) {
+      _log.severe("[getBinary] Failed requesting server: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+    return response.body;
+  }
+
+  @override
+  putBinary(Account account, String path, Uint8List content) async {
+    _log.info("[putBinary] $path");
+    final response =
+        await Api(account).files().put(path: path, content: content);
+    if (!response.isGood) {
+      _log.severe("[putBinary] Failed requesting server: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+  }
+
+  @override
+  updateMetadata(Account account, File f, Metadata metadata) async {
+    _log.info("[updateMetadata] ${f.path}");
+    if (metadata != null && metadata.fileEtag != f.etag) {
+      _log.warning(
+          "[updateMetadata] etag mismatch (metadata: ${metadata.fileEtag}, file: ${f.etag})");
+    }
+    final setProps = {
+      if (metadata != null) "app:metadata": jsonEncode(metadata.toJson()),
+    };
+    final removeProps = [
+      if (metadata == null) "app:metadata",
+    ];
+    final response = await Api(account).files().proppatch(
+          path: f.path,
+          namespaces: {
+            "com.nkming.nc_photos": "app",
+          },
+          set: setProps.isNotEmpty ? setProps : null,
+          remove: removeProps.isNotEmpty ? removeProps : null,
+        );
+    if (!response.isGood) {
+      _log.severe("[updateMetadata] Failed requesting server: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+  }
+
+  @override
+  copy(
+    Account account,
+    File f,
+    String destination, {
+    bool shouldOverwrite,
+  }) async {
+    _log.info("[copy] ${f.path} to $destination");
+    final response = await Api(account).files().copy(
+          path: f.path,
+          destinationUrl: "${account.url}/$destination",
+          overwrite: shouldOverwrite,
+        );
+    if (!response.isGood) {
+      _log.severe("[copy] Failed requesting sever: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+  }
+
+  @override
+  move(
+    Account account,
+    File f,
+    String destination, {
+    bool shouldOverwrite,
+  }) async {
+    _log.info("[move] ${f.path} to $destination");
+    final response = await Api(account).files().move(
+          path: f.path,
+          destinationUrl: "${account.url}/$destination",
+          overwrite: shouldOverwrite,
+        );
+    if (!response.isGood) {
+      _log.severe("[move] Failed requesting sever: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+  }
+
+  @override
+  createDir(Account account, String path) async {
+    _log.info("[createDir] $path");
+    final response = await Api(account).files().mkcol(
+          path: path,
+        );
+    if (!response.isGood) {
+      _log.severe("[createDir] Failed requesting sever: $response");
+      throw ApiException(
+          response: response,
+          message: "Failed communicating with server: ${response.statusCode}");
+    }
+  }
+
+  static final _log = Logger("entity.file.data_source.FileWebdavDataSource");
+}
+
+class FileAppDbDataSource implements FileDataSource {
+  @override
+  list(Account account, File f) {
+    _log.info("[list] ${f.path}");
+    return AppDb.use((db) async {
+      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadOnly);
+      final store = transaction.objectStore(AppDb.fileStoreName);
+      return await _doList(store, account, f);
+    });
+  }
+
+  @override
+  remove(Account account, File f) {
+    _log.info("[remove] ${f.path}");
+    return AppDb.use((db) async {
+      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
+      final store = transaction.objectStore(AppDb.fileStoreName);
+      final index = store.index(AppDbFileEntry.indexName);
+      final path = AppDbFileEntry.toPath(account, f);
+      final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
+      final keys = await index
+          .openKeyCursor(range: range, autoAdvance: true)
+          .map((cursor) => cursor.primaryKey)
+          .toList();
+      for (final k in keys) {
+        _log.fine("[remove] Removing DB entry: $k");
+        await store.delete(k);
+      }
+    });
+  }
+
+  @override
+  getBinary(Account account, File f) {
+    _log.info("[getBinary] ${f.path}");
+    throw UnimplementedError();
+  }
+
+  @override
+  putBinary(Account account, String path, Uint8List content) async {
+    _log.info("[putBinary] $path");
+    // do nothing, we currently don't store file contents locally
+  }
+
+  @override
+  updateMetadata(Account account, File f, Metadata metadata) {
+    _log.info("[updateMetadata] ${f.path}");
+    return AppDb.use((db) async {
+      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
+      final store = transaction.objectStore(AppDb.fileStoreName);
+      final parentDir = File(path: path.dirname(f.path));
+      final parentList = await _doList(store, account, parentDir);
+      final jsonList = parentList.map((e) {
+        if (e.path == f.path) {
+          return e.copyWith(metadata: OrNull(metadata));
+        } else {
+          return e;
+        }
+      });
+      await _cacheListResults(store, account, parentDir, jsonList);
+    });
+  }
+
+  @override
+  copy(
+    Account account,
+    File f,
+    String destination, {
+    bool shouldOverwrite,
+  }) async {
+    // do nothing
+  }
+
+  @override
+  move(
+    Account account,
+    File f,
+    String destination, {
+    bool shouldOverwrite,
+  }) async {
+    // do nothing
+  }
+
+  @override
+  createDir(Account account, String path) async {
+    // do nothing
+  }
+
+  Future<List<File>> _doList(ObjectStore store, Account account, File f) async {
+    final index = store.index(AppDbFileEntry.indexName);
+    final path = AppDbFileEntry.toPath(account, f);
+    final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
+    final List results = await index.getAll(range);
+    if (results?.isNotEmpty == true) {
+      final entries = results
+          .map((e) => AppDbFileEntry.fromJson(e.cast<String, dynamic>()));
+      return entries.map((e) {
+        _log.info("[_doList] ${e.path}[${e.index}]");
+        return e.data;
+      }).reduce((value, element) => value + element);
+    } else {
+      throw CacheNotFoundException("No entry: $path");
+    }
+  }
+
+  static final _log = Logger("entity.file.data_source.FileAppDbDataSource");
+}
+
+class FileCachedDataSource implements FileDataSource {
+  FileCachedDataSource({
+    this.shouldCheckCache = false,
+  });
+
+  @override
+  list(Account account, File f) async {
+    final cacheManager = _CacheManager(
+      appDbSrc: _appDbSrc,
+      remoteSrc: _remoteSrc,
+      shouldCheckCache: shouldCheckCache,
+    );
+    final cache = await cacheManager.list(account, f);
+    if (cacheManager.isGood) {
+      return cache;
+    }
+
+    // no cache or outdated
+    try {
+      final remote = await _remoteSrc.list(account, f);
+      await _cacheResult(account, f, remote);
+      if (shouldCheckCache) {
+        // update our local touch token to match the remote one
+        final tokenManager = TouchTokenManager();
+        try {
+          await tokenManager.setLocalToken(
+              account, f, cacheManager.remoteTouchToken);
+        } catch (e, stacktrace) {
+          _log.shout("[list] Failed while setLocalToken", e, stacktrace);
+          // ignore error
+        }
+      }
+
+      if (cache != null) {
+        try {
+          await _cleanUpCachedDir(account, remote, cache);
+        } catch (e, stacktrace) {
+          _log.shout("[list] Failed while _cleanUpCachedList", e, stacktrace);
+          // ignore error
+        }
+      }
+      return remote;
+    } on ApiException catch (e) {
+      if (e.response.statusCode == 404) {
+        _log.info("[list] File removed: $f");
+        _appDbSrc.remove(account, f);
+        return [];
+      } else {
+        rethrow;
+      }
+    }
+  }
+
+  @override
+  remove(Account account, File f) async {
+    await _appDbSrc.remove(account, f);
+    await _remoteSrc.remove(account, f);
+  }
+
+  @override
+  getBinary(Account account, File f) {
+    return _remoteSrc.getBinary(account, f);
+  }
+
+  @override
+  putBinary(Account account, String path, Uint8List content) async {
+    await _remoteSrc.putBinary(account, path, content);
+  }
+
+  @override
+  updateMetadata(Account account, File f, Metadata metadata) async {
+    await _remoteSrc
+        .updateMetadata(account, f, metadata)
+        .then((_) => _appDbSrc.updateMetadata(account, f, metadata));
+
+    // generate a new random token
+    final token = Uuid().v4().replaceAll("-", "");
+    final tokenManager = TouchTokenManager();
+    final dir = File(path: path.dirname(f.path));
+    await tokenManager.setLocalToken(account, dir, token);
+    final fileRepo = FileRepo(this);
+    await tokenManager.setRemoteToken(fileRepo, account, dir, token);
+    _log.info(
+        "[updateMetadata] New touch token '$token' for dir '${dir.path}'");
+  }
+
+  @override
+  copy(
+    Account account,
+    File f,
+    String destination, {
+    bool shouldOverwrite,
+  }) async {
+    await _remoteSrc.copy(account, f, destination,
+        shouldOverwrite: shouldOverwrite);
+  }
+
+  @override
+  move(
+    Account account,
+    File f,
+    String destination, {
+    bool shouldOverwrite,
+  }) async {
+    await _remoteSrc.move(account, f, destination,
+        shouldOverwrite: shouldOverwrite);
+  }
+
+  @override
+  createDir(Account account, String path) async {
+    await _remoteSrc.createDir(account, path);
+  }
+
+  Future<void> _cacheResult(Account account, File f, List<File> result) {
+    return AppDb.use((db) async {
+      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
+      final store = transaction.objectStore(AppDb.fileStoreName);
+      await _cacheListResults(store, account, f, result);
+    });
+  }
+
+  /// Remove dangling dir entries in the file object store
+  Future<void> _cleanUpCachedDir(
+      Account account, List<File> remoteResults, List<File> cachedResults) {
+    final removed = cachedResults
+        .where((cache) =>
+            !remoteResults.any((remote) => remote.path == cache.path))
+        .toList();
+    if (removed.isEmpty) {
+      return Future.delayed(Duration.zero);
+    }
+    return AppDb.use((db) async {
+      final transaction = db.transaction(AppDb.fileStoreName, idbModeReadWrite);
+      final store = transaction.objectStore(AppDb.fileStoreName);
+      final index = store.index(AppDbFileEntry.indexName);
+      for (final r in removed) {
+        final path = AppDbFileEntry.toPath(account, r);
+        final keys = [];
+        // delete the dir itself
+        final dirRange = KeyRange.bound([path, 0], [path, int_util.int32Max]);
+        // delete with KeyRange is not supported in idb_shim/idb_sqflite
+        // await store.delete(dirRange);
+        keys.addAll(await index
+            .openKeyCursor(range: dirRange, autoAdvance: true)
+            .map((cursor) => cursor.primaryKey)
+            .toList());
+        // then its children
+        final childrenRange =
+            KeyRange.bound(["$path/", 0], ["$path/\uffff", int_util.int32Max]);
+        keys.addAll(await index
+            .openKeyCursor(range: childrenRange, autoAdvance: true)
+            .map((cursor) => cursor.primaryKey)
+            .toList());
+
+        for (final k in keys) {
+          _log.fine("[_cleanUpCachedDir] Removing DB entry: $k");
+          await store.delete(k);
+        }
+      }
+    });
+  }
+
+  final bool shouldCheckCache;
+
+  final _remoteSrc = FileWebdavDataSource();
+  final _appDbSrc = FileAppDbDataSource();
+
+  static final _log = Logger("entity.file.data_source.FileCachedDataSource");
+}
+
+class _CacheManager {
+  _CacheManager({
+    @required this.appDbSrc,
+    @required this.remoteSrc,
+    this.shouldCheckCache = false,
+  });
+
+  /// Return the cached results of listing a directory [f]
+  ///
+  /// Should check [isGood] before using the cache returning by this method
+  Future<List<File>> list(Account account, File f) async {
+    final trimmedRootPath = f.path.trimAny("/");
+    List<File> cache;
+    try {
+      cache = await appDbSrc.list(account, f);
+      // compare the cached root
+      final cacheEtag = cache
+          .firstWhere((element) => element.path.trimAny("/") == trimmedRootPath)
+          .etag;
+      if (cacheEtag != null) {
+        // compare the etag to see if the content has been updated
+        var remoteEtag = f.etag;
+        if (remoteEtag == null) {
+          // no etag supplied, we need to query it form remote
+          final remote = await remoteSrc.list(account, f, depth: 0);
+          assert(remote.length == 1);
+          remoteEtag = remote.first.etag;
+        }
+        if (cacheEtag == remoteEtag) {
+          _log.fine(
+              "[_listCache] etag matched for ${AppDbFileEntry.toPath(account, f)}");
+          if (shouldCheckCache) {
+            await _checkTouchToken(account, f, cache);
+          } else {
+            _isGood = true;
+          }
+        }
+      } else {
+        _log.info(
+            "[_list] Remote content updated for ${AppDbFileEntry.toPath(account, f)}");
+      }
+    } on CacheNotFoundException catch (_) {
+      // normal when there's no cache
+    } catch (e, stacktrace) {
+      _log.shout("[_list] Cache failure", e, stacktrace);
+    }
+    return cache;
+  }
+
+  bool get isGood => _isGood;
+  String get remoteTouchToken => _remoteToken;
+
+  Future<void> _checkTouchToken(
+      Account account, File f, List<File> cache) async {
+    final touchPath =
+        "${remote_storage_util.getRemoteTouchDir(account)}/${f.strippedPath}";
+    final fileRepo = FileRepo(FileCachedDataSource());
+    final tokenManager = TouchTokenManager();
+    String remoteToken;
+    try {
+      remoteToken = await tokenManager.getRemoteToken(fileRepo, account, f);
+    } catch (e, stacktrace) {
+      _log.shout(
+          "[_checkTouchToken] Failed getting remote token at '$touchPath'",
+          e,
+          stacktrace);
+    }
+    _remoteToken = remoteToken;
+
+    String localToken;
+    try {
+      localToken = await tokenManager.getLocalToken(account, f);
+    } catch (e, stacktrace) {
+      _log.shout(
+          "[_checkTouchToken] Failed getting local token at '$touchPath'",
+          e,
+          stacktrace);
+    }
+
+    if (localToken != remoteToken) {
+      _log.info(
+          "[_checkTouchToken] Remote and local token differ, cache outdated");
+    } else {
+      _isGood = true;
+    }
+  }
+
+  final FileWebdavDataSource remoteSrc;
+  final FileAppDbDataSource appDbSrc;
+  final bool shouldCheckCache;
+
+  var _isGood = false;
+  String _remoteToken;
+
+  static final _log = Logger("entity.file.data_source._CacheManager");
+}
+
+Future<void> _cacheListResults(
+    ObjectStore store, Account account, File f, Iterable<File> results) async {
+  final index = store.index(AppDbFileEntry.indexName);
+  final path = AppDbFileEntry.toPath(account, f);
+  final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
+  // count number of entries for this dir
+  final count = await index.count(range);
+  int newCount = 0;
+  for (final pair
+      in partition(results, AppDbFileEntry.maxDataSize).withIndex()) {
+    _log.info(
+        "[_cacheListResults] Caching $path[${pair.item1}], length: ${pair.item2.length}");
+    await store.put(
+      AppDbFileEntry(path, pair.item1, pair.item2).toJson(),
+      AppDbFileEntry.toPrimaryKey(account, f, pair.item1),
+    );
+    ++newCount;
+  }
+  if (count > newCount) {
+    // index is 0-based
+    final rmRange = KeyRange.bound([path, newCount], [path, int_util.int32Max]);
+    final rmKeys = await index
+        .openKeyCursor(range: rmRange, autoAdvance: true)
+        .map((cursor) => cursor.primaryKey)
+        .toList();
+    for (final k in rmKeys) {
+      _log.fine("[_cacheListResults] Removing DB entry: $k");
+      await store.delete(k);
+    }
+  }
+}
+
+final _log = Logger("entity.file.data_source");
diff --git a/lib/metadata_task_manager.dart b/lib/metadata_task_manager.dart
index 49d8628a..2068f065 100644
--- a/lib/metadata_task_manager.dart
+++ b/lib/metadata_task_manager.dart
@@ -4,6 +4,7 @@ import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/api/api_util.dart' as api_util;
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/pref.dart';
 import 'package:nc_photos/use_case/update_missing_metadata.dart';
 
diff --git a/lib/mobile/downloader.dart b/lib/mobile/downloader.dart
index 93f3508b..e6444ae2 100644
--- a/lib/mobile/downloader.dart
+++ b/lib/mobile/downloader.dart
@@ -3,6 +3,7 @@ import 'dart:io';
 import 'package:flutter/services.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/exception.dart';
 import 'package:nc_photos/mobile/android/media_store.dart';
 import 'package:nc_photos/platform/downloader.dart' as itf;
diff --git a/lib/use_case/update_missing_metadata.dart b/lib/use_case/update_missing_metadata.dart
index 482cd670..e6eaaae1 100644
--- a/lib/use_case/update_missing_metadata.dart
+++ b/lib/use_case/update_missing_metadata.dart
@@ -4,6 +4,7 @@ import 'package:nc_photos/connectivity_util.dart' as connectivity_util;
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/exif.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/mobile/platform.dart'
     if (dart.library.html) 'package:nc_photos/web/platform.dart' as platform;
 import 'package:nc_photos/use_case/scan_missing_metadata.dart';
diff --git a/lib/web/downloader.dart b/lib/web/downloader.dart
index c4890295..cb114fc4 100644
--- a/lib/web/downloader.dart
+++ b/lib/web/downloader.dart
@@ -5,6 +5,7 @@ import 'dart:js' as js;
 
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/platform/downloader.dart' as itf;
 import 'package:path/path.dart' as path;
 
diff --git a/lib/widget/home_albums.dart b/lib/widget/home_albums.dart
index a4a172bd..43e24c76 100644
--- a/lib/widget/home_albums.dart
+++ b/lib/widget/home_albums.dart
@@ -13,6 +13,7 @@ import 'package:nc_photos/api/api_util.dart' as api_util;
 import 'package:nc_photos/bloc/list_album.dart';
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/entity/file_util.dart' as file_util;
 import 'package:nc_photos/exception_util.dart' as exception_util;
 import 'package:nc_photos/iterable_extension.dart';
diff --git a/lib/widget/home_photos.dart b/lib/widget/home_photos.dart
index f66b99ec..052b8c54 100644
--- a/lib/widget/home_photos.dart
+++ b/lib/widget/home_photos.dart
@@ -13,6 +13,7 @@ import 'package:nc_photos/api/api_util.dart' as api_util;
 import 'package:nc_photos/bloc/scan_dir.dart';
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/entity/file_util.dart' as file_util;
 import 'package:nc_photos/exception_util.dart' as exception_util;
 import 'package:nc_photos/iterable_extension.dart';
diff --git a/lib/widget/viewer.dart b/lib/widget/viewer.dart
index 166bd887..99332405 100644
--- a/lib/widget/viewer.dart
+++ b/lib/widget/viewer.dart
@@ -9,6 +9,7 @@ import 'package:logging/logging.dart';
 import 'package:nc_photos/account.dart';
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/entity/file_util.dart' as file_util;
 import 'package:nc_photos/exception.dart';
 import 'package:nc_photos/exception_util.dart' as exception_util;
diff --git a/lib/widget/viewer_detail_pane.dart b/lib/widget/viewer_detail_pane.dart
index a67ee80c..68a1ee94 100644
--- a/lib/widget/viewer_detail_pane.dart
+++ b/lib/widget/viewer_detail_pane.dart
@@ -13,6 +13,7 @@ import 'package:nc_photos/double_extension.dart';
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/exif.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/entity/file/data_source.dart';
 import 'package:nc_photos/exception_util.dart' as exception_util;
 import 'package:nc_photos/iterable_extension.dart';
 import 'package:nc_photos/k.dart' as k;