feat: implement region detection based on timezone and locale

lib/features/intro/widget/intro_page.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -17,7 +18,6 @@ import 'package:hiddify/features/settings/data/config_option_repository.dart';
 import 'package:hiddify/gen/assets.gen.dart';
 import 'package:hiddify/utils/utils.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
-import 'package:timezone_to_country/timezone_to_country.dart';
 
 class IntroPage extends HookConsumerWidget with PresLogger {
   const IntroPage({super.key});
@@ -182,7 +182,7 @@ class IntroPage extends HookConsumerWidget with PresLogger {
 
   Future<void> autoSelectRegion(WidgetRef ref) async {
     try {
-      final countryCode = await TimeZoneToCountry.getLocalCountryCode();
+      final countryCode = RegionDetector.detect();
       final regionLocale = _getRegionLocale(countryCode);
       loggy.debug('Timezone Region: ${regionLocale.region} Locale: ${regionLocale.locale}');
       await ref.read(ConfigOptions.region.notifier).update(regionLocale.region);
@@ -227,9 +227,9 @@ class IntroPage extends HookConsumerWidget with PresLogger {
       case "AF":
         return RegionLocale(Region.af, AppLocale.fa);
       case "BR":
-        return RegionLocale(Region.other, AppLocale.ptBr);
+        return RegionLocale(Region.br, AppLocale.ptBr);
       case "TR":
-        return RegionLocale(Region.other, AppLocale.tr);
+        return RegionLocale(Region.tr, AppLocale.tr);
       default:
         return RegionLocale(Region.other, AppLocale.en);
     }
@@ -242,3 +242,181 @@ class RegionLocale {
 
   RegionLocale(this.region, this.locale);
 }
+
+class RegionDetector {
+  /// Returns: 'IR' | 'AF' | 'CN' | 'TR' | 'RU' | 'BR' | 'US'
+  static String detect() {
+    final now = DateTime.now();
+    final offset = now.timeZoneOffset.inMinutes;
+    final tz = now.timeZoneName.toLowerCase().trim();
+
+    if (offset == 210) return 'IR';
+
+    if (offset == 270) {
+      final (_, country) = _parseLocale();
+      return country == 'IR' ? 'IR' : 'AF';
+    }
+
+    final fromName = _fromTzName(tz, offset);
+    if (fromName != null) return fromName;
+
+    final candidates = _candidatesForOffset(offset);
+    if (candidates.isEmpty) return 'US';
+
+    return _resolveByLocale(candidates);
+  }
+
+  static String? _fromTzName(String tz, int offset) {
+    if (tz.contains('/')) {
+      final city = tz.split('/').last.replaceAll(' ', '_');
+      final r = _ianaCities[city];
+      if (r != null) return r;
+    }
+
+    if (tz == 'irst' || tz == 'irdt' || tz.contains('iran')) return 'IR';
+
+    if (tz == 'aft' || tz.contains('afghanistan')) return 'AF';
+
+    if (tz == 'trt' || tz.contains('turkey') || tz.contains('istanbul')) {
+      return 'TR';
+    }
+
+    if (tz.contains('china') || tz.contains('beijing')) return 'CN';
+    if (tz == 'cst' && offset == 480) return 'CN';
+
+    if (_matchesRussiaTz(tz)) return 'RU';
+
+    if (_matchesBrazilTz(tz)) return 'BR';
+
+    return null;
+  }
+
+  static bool _matchesRussiaTz(String tz) {
+    if (tz.contains('russia') || tz.contains('moscow')) return true;
+
+    const abbrs = {'msk', 'yekt', 'omst', 'krat', 'irkt', 'yakt', 'vlat', 'magt', 'pett', 'sakt', 'sret'};
+    if (abbrs.contains(tz)) return true;
+
+    const winKeys = [
+      'ekaterinburg',
+      'kaliningrad',
+      'yakutsk',
+      'vladivostok',
+      'magadan',
+      'sakhalin',
+      'kamchatka',
+      'astrakhan',
+      'saratov',
+      'volgograd',
+      'altai',
+      'tomsk',
+      'transbaikal',
+      'n. central asia',
+      'north asia',
+    ];
+    return winKeys.any(tz.contains);
+  }
+
+  static bool _matchesBrazilTz(String tz) {
+    if (tz == 'brt' || tz == 'brst') return true;
+    if (tz.contains('brazil') || tz.contains('brasilia')) return true;
+
+    const winKeys = ['e. south america', 'central brazilian', 'tocantins', 'bahia'];
+    return winKeys.any(tz.contains);
+  }
+
+  static Set<String> _candidatesForOffset(int offset) {
+    final c = <String>{};
+
+    if (offset == 180) c.add('TR');
+
+    if (offset == 480) c.add('CN');
+
+    if (_ruOffsets.contains(offset)) c.add('RU');
+
+    if (_brOffsets.contains(offset)) c.add('BR');
+
+    return c;
+  }
+
+  static const _ruOffsets = {120, 180, 240, 300, 360, 420, 480, 540, 600, 660, 720};
+
+  static const _brOffsets = {-120, -180, -240, -300};
+
+  static String _resolveByLocale(Set<String> candidates) {
+    final (lang, country) = _parseLocale();
+
+    if (country != null && candidates.contains(country)) {
+      return country;
+    }
+
+    final regionFromLang = _langToRegion[lang];
+    if (regionFromLang != null && candidates.contains(regionFromLang)) {
+      return regionFromLang;
+    }
+
+    return 'US';
+  }
+
+  static (String, String?) _parseLocale() {
+    try {
+      final parts = Platform.localeName.split(RegExp(r'[_\-.]'));
+      final lang = parts.first.toLowerCase();
+
+      String? country;
+      for (final p in parts.skip(1)) {
+        if (p.length == 2) {
+          country = p.toUpperCase();
+          break;
+        }
+      }
+
+      return (lang, country);
+    } catch (_) {
+      return ('en', null);
+    }
+  }
+
+  static const _langToRegion = <String, String>{'fa': 'IR', 'ps': 'AF', 'tr': 'TR', 'zh': 'CN', 'ru': 'RU', 'pt': 'BR'};
+
+  static const _ianaCities = <String, String>{
+    'tehran': 'IR',
+    'kabul': 'AF',
+    'istanbul': 'TR',
+    'shanghai': 'CN',
+    'chongqing': 'CN',
+    'urumqi': 'CN',
+    'harbin': 'CN',
+    'moscow': 'RU',
+    'kaliningrad': 'RU',
+    'samara': 'RU',
+    'yekaterinburg': 'RU',
+    'omsk': 'RU',
+    'novosibirsk': 'RU',
+    'barnaul': 'RU',
+    'tomsk': 'RU',
+    'krasnoyarsk': 'RU',
+    'irkutsk': 'RU',
+    'chita': 'RU',
+    'yakutsk': 'RU',
+    'vladivostok': 'RU',
+    'magadan': 'RU',
+    'sakhalin': 'RU',
+    'kamchatka': 'RU',
+    'anadyr': 'RU',
+    'volgograd': 'RU',
+    'saratov': 'RU',
+    'astrakhan': 'RU',
+    'sao_paulo': 'BR',
+    'fortaleza': 'BR',
+    'recife': 'BR',
+    'manaus': 'BR',
+    'belem': 'BR',
+    'cuiaba': 'BR',
+    'bahia': 'BR',
+    'rio_branco': 'BR',
+    'noronha': 'BR',
+    'porto_velho': 'BR',
+    'campo_grande': 'BR',
+  };
+}