clean up build

lib/theming/theme_service.dart

@@ -0,0 +1,54 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'themes/themes.dart';
+
+class ThemeService {
+  ThemeService._();
+  static late SharedPreferences prefs;
+  static ThemeService? _instance;
+
+  static Future<ThemeService> get instance async {
+    if (_instance == null) {
+      prefs = await SharedPreferences.getInstance();
+      _instance = ThemeService._();
+    }
+    return _instance!;
+  }
+
+  final allThemes = <String, ThemeData>{
+    'dark': darkTheme,
+    'light': lightTheme,
+  };
+
+  String get previousThemeName {
+    String? themeName = prefs.getString('previousThemeName');
+    if (themeName == null) {
+      final isPlatformDark =
+          WidgetsBinding.instance.window.platformBrightness == Brightness.dark;
+      themeName = isPlatformDark ? 'light' : 'dark';
+    }
+    return themeName;
+  }
+
+  get initial {
+    String? themeName = prefs.getString('theme');
+    if (themeName == null) {
+      final isPlatformDark =
+          WidgetsBinding.instance.window.platformBrightness == Brightness.dark;
+      themeName = isPlatformDark ? 'dark' : 'light';
+    }
+    return allThemes[themeName];
+  }
+
+  save(String newThemeName) {
+    var currentThemeName = prefs.getString('theme');
+    if (currentThemeName != null) {
+      prefs.setString('previousThemeName', currentThemeName);
+    }
+    prefs.setString('theme', newThemeName);
+  }
+
+  ThemeData getByName(String name) {
+    return allThemes[name]!;
+  }
+}