fix(storage): FoldersStorage.save is one transaction, load() retries after a failure (#1767)

lib/core/storage/folder_repository.dart

@@ -55,6 +55,32 @@ class FolderRepository {
     await db.delete('folders');
   }
 
+  /// Makes the stored folders exactly [names], in one transaction: a failure
+  /// leaves the old list. Folders that stay keep their connections; the ones
+  /// that go release theirs first (see [removeFolder]).
+  Future<void> replaceFolders(List<String> names) async {
+    final wanted = <String>{
+      for (final name in names)
+        if (name.trim().isNotEmpty) name.trim(),
+    };
+    final db = await _open();
+    await db.transaction((txn) async {
+      final rows = await txn.query('folders', columns: ['name']);
+      final existing = {for (final r in rows) r['name'] as String};
+      for (final name in existing.difference(wanted)) {
+        await txn.rawUpdate(
+          'UPDATE connections SET folder_id = NULL WHERE folder_id IN '
+          '(SELECT id FROM folders WHERE name = ?)',
+          [name],
+        );
+        await txn.delete('folders', where: 'name = ?', whereArgs: [name]);
+      }
+      for (final name in wanted.difference(existing)) {
+        await txn.insert('folders', {'name': name});
+      }
+    });
+  }
+
   Future<int?> getFolderIdByName(String name) async {
     final db = await _open();
     final rows = await db.query('folders',

lib/core/storage/folders_storage.dart

@@ -26,11 +26,13 @@ class FoldersStorage {
     try {
       await _migrateFromLegacyIfNeeded();
       _folders = await LocalDb.instance.getFolders();
+      _loaded = true;
     } catch (e) {
+      // Not marked loaded: the next call reads again instead of caching an
+      // empty list for the rest of the session.
       debugPrint('FoldersStorage.load: $e');
       _folders = [];
     }
-    _loaded = true;
     return folders;
   }
 
@@ -64,11 +66,8 @@ class FoldersStorage {
   }
 
   Future<void> save(List<String> folders) async {
-    _folders = List.from(folders);
-    await LocalDb.instance.clearFolders();
-    for (final name in _folders) {
-      await LocalDb.instance.addFolder(name);
-    }
+    await LocalDb.instance.replaceFolders(folders);
+    _folders = await LocalDb.instance.getFolders();
   }
 
   Future<void> add(String name) async {

lib/core/storage/local_db.dart

@@ -135,6 +135,9 @@ class LocalDb {
 
   Future<void> clearFolders() => folders.clearFolders();
 
+  Future<void> replaceFolders(List<String> names) =>
+      folders.replaceFolders(names);
+
   Future<int?> getFolderIdByName(String name) =>
       folders.getFolderIdByName(name);
 

test/core/storage/storage_repositories_test.dart

@@ -51,6 +51,33 @@ void main() {
     expect(rows.single['folder_id'], isNull);
   });
 
+  test('folders: replaceFolders is all-or-nothing and keeps the connections',
+      () async {
+    final folders = FolderRepository(open);
+    await folders.addFolder('work');
+    await folders.addFolder('home');
+    final workId = await folders.getFolderIdByName('work');
+    final homeId = await folders.getFolderIdByName('home');
+    final inWork = await insertConnection(folderId: workId);
+    final inHome = await insertConnection(folderId: homeId);
+
+    await folders.replaceFolders(['work', ' new ', '', 'work']);
+
+    expect(await folders.getFolders(), ['new', 'work']);
+    expect(await folders.getFolderIdByName('work'), workId);
+    final kept = await db.query('connections', where: 'id = ?', whereArgs: [inWork]);
+    expect(kept.single['folder_id'], workId);
+    final released = await db.query('connections', where: 'id = ?', whereArgs: [inHome]);
+    expect(released.single['folder_id'], isNull);
+
+    // A name the table refuses mid-way rolls the whole replace back.
+    await db.execute(
+        'CREATE TRIGGER no_boom BEFORE INSERT ON folders '
+        "WHEN NEW.name = 'boom' BEGIN SELECT RAISE(ABORT, 'boom'); END");
+    await expectLater(folders.replaceFolders(['zzz', 'boom']), throwsA(anything));
+    expect(await folders.getFolders(), ['new', 'work']);
+  });
+
   test('app settings: set, replace, delete and ER layouts per scope', () async {
     final settings = AppSettingsRepository(open);
     expect(await settings.getAppSetting('k'), isNull);