feat(proj): init

mobile/lib/theme/theme_controller.dart

@@ -0,0 +1,81 @@
+import 'package:flutter/cupertino.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+enum ThemePreference {
+  system,
+  light,
+  dark;
+
+  static ThemePreference parse(String? raw) {
+    return switch (raw) {
+      'light' => ThemePreference.light,
+      'dark' => ThemePreference.dark,
+      _ => ThemePreference.system,
+    };
+  }
+
+  Brightness resolve(Brightness platform) => switch (this) {
+        ThemePreference.system => platform,
+        ThemePreference.light => Brightness.light,
+        ThemePreference.dark => Brightness.dark,
+      };
+}
+
+abstract interface class ThemePreferenceStore {
+  Future<String?> read();
+  Future<void> write(String value);
+}
+
+class PrefsThemeStore implements ThemePreferenceStore {
+  const PrefsThemeStore();
+
+  static const key = 'ppm_theme_preference';
+
+  @override
+  Future<String?> read() async {
+    final prefs = await SharedPreferences.getInstance();
+    return prefs.getString(key);
+  }
+
+  @override
+  Future<void> write(String value) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(key, value);
+  }
+}
+
+class MemoryThemeStore implements ThemePreferenceStore {
+  MemoryThemeStore([this.value]);
+
+  String? value;
+
+  @override
+  Future<String?> read() async => value;
+
+  @override
+  Future<void> write(String next) async => value = next;
+}
+
+/// Survives logout: appearance is a device preference, not a session one.
+class ThemeController extends ChangeNotifier {
+  ThemeController({ThemePreferenceStore? store}) : _store = store ?? const PrefsThemeStore();
+
+  final ThemePreferenceStore _store;
+  ThemePreference _preference = ThemePreference.system;
+
+  ThemePreference get preference => _preference;
+
+  Brightness resolve(Brightness platform) => _preference.resolve(platform);
+
+  Future<void> restore() async {
+    _preference = ThemePreference.parse(await _store.read());
+    notifyListeners();
+  }
+
+  Future<void> setPreference(ThemePreference value) async {
+    if (_preference == value) return;
+    _preference = value;
+    notifyListeners();
+    await _store.write(value.name);
+  }
+}