Frontend first draft

frontend/pweb/lib/app/locale_manager.dart

@@ -0,0 +1,70 @@
+import 'package:flutter/material.dart';
+
+import 'package:intl/find_locale.dart';
+
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'package:pshared/provider/locale.dart';
+
+
+String _localeVarStorageName() {
+  return 'mcrm_last_locale';
+}
+
+Locale _selectDefaultLocale(List<Locale> appLocales, Locale defaultLocale) {
+  return appLocales.contains(defaultLocale) 
+    ? defaultLocale 
+    : appLocales.isEmpty 
+      ? throw ArgumentError('empty application locales list', 'appLocales') 
+      : appLocales.first;
+}
+
+
+class LocaleManager {
+  late SharedPreferences _prefs;
+  final List<Locale> appLocales;
+  final Locale _defaultLocale;
+  final LocaleProvider localeProvider;
+
+  LocaleManager(this.localeProvider, this.appLocales, Locale defaultLocale) 
+    : _defaultLocale = _selectDefaultLocale(appLocales, defaultLocale) {
+    SharedPreferences.getInstance().then((prefs) {
+      _prefs = prefs;
+      _initializeLocaleProvider();
+    });
+  }
+
+  Future<void> _initializeLocaleProvider() async {
+    final initialLocale = await _getInitialLocale();
+    localeProvider.setLocale(initialLocale);
+    localeProvider.addListener(_onLocaleChanged);
+  }
+
+  Future<Locale> _getInitialLocale() async {
+    final locale = await _pickLocale();
+    return appLocales.contains(locale) ? locale : _defaultLocale;
+  }
+
+  Future<Locale> _pickLocale() async {
+    String? savedLocaleCode = _prefs.getString(_localeVarStorageName());
+    if (savedLocaleCode != null) {
+      return Locale(savedLocaleCode);
+    }
+
+    String systemLocaleString = await findSystemLocale();
+    final List<String> localeParts = systemLocaleString.split('_');
+    final Locale systemLocale = Locale(localeParts[0]);
+
+    final res = appLocales.contains(systemLocale);
+
+    return res ? systemLocale : _defaultLocale;
+  }
+
+  Future<bool> saveLocale(Locale locale) async {
+    return _prefs.setString(_localeVarStorageName(), locale.toString());
+  }
+
+  Future<bool> _onLocaleChanged() async {
+    return saveLocale(localeProvider.locale);
+  }
+}