import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

/// Single source of truth for app language (Group-2).
/// Drives BOTH systems together:
/// - ARB static words via MaterialApp.locale (AppLocalizations)
/// - wireframe field words via DynamicStrings.tr(key) backed by
///   assets/translations_dynamic/{lang}.json (free, offline, KBs).
/// Revert: remove provider wiring in main.dart; generated screens fall back
/// to English keys (DynamicStrings.tr returns readable fallback, never crash).
class LocaleProvider with ChangeNotifier {
  static const _prefKey = 'app_locale_code';
  static const supportedCodes = ['en', 'hi'];

  Locale _locale = const Locale('en');
  Locale get locale => _locale;
  String get code => _locale.languageCode;

  /// lang -> (key -> translated value). Embedded assets loaded once at startup.
  final Map<String, Map<String, String>> _tables = {};

  /// Server-supplied diff cache (future: portal-backend translations API).
  /// Key format: "lang::key" -> value, persisted to SharedPreferences.
  final Map<String, String> _serverDiff = {};

  bool _ready = false;
  bool get ready => _ready;

  Future<void> init() async {
    final prefs = await SharedPreferences.getInstance();
    final saved = prefs.getString(_prefKey);
    if (saved != null && supportedCodes.contains(saved)) {
      _locale = Locale(saved);
    }
    _ready = true;
    notifyListeners();
  }

  /// Called once from bootstrap with preloaded asset tables.
  void seedTables(Map<String, Map<String, String>> tables) {
    _tables.addAll(tables);
  }

  /// Merge server diff (new wireframe fields added after release).
  /// Works offline afterwards because diff is persisted.
  Future<void> updateFromServer(Map<String, String> words, String lang) async {
    if (words.isEmpty) return;
    final table = _tables.putIfAbsent(lang, () => {});
    table.addAll(words);
    for (final e in words.entries) {
      _serverDiff['$lang::${e.key}'] = e.value;
    }
    final prefs = await SharedPreferences.getInstance();
    // Persist each entry individually to survive restarts (small volume).
    for (final e in words.entries) {
      await prefs.setString('dyn_${lang}_${e.key}', e.value);
    }
    notifyListeners();
  }

  Future<void> loadServerCache() async {
    final prefs = await SharedPreferences.getInstance();
    for (final lang in supportedCodes) {
      final table = _tables.putIfAbsent(lang, () => {});
      for (final key in prefs.getKeys().where((k) => k.startsWith('dyn_${lang}_'))) {
        final field = key.substring('dyn_${lang}_'.length);
        final v = prefs.getString(key);
        if (v != null) table[field] = v;
      }
    }
    notifyListeners();
  }

  Future<void> setLocale(String code) async {
    if (!supportedCodes.contains(code)) return;
    _locale = Locale(code);
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_prefKey, code);
    notifyListeners();
  }

  /// Runtime lookup for wireframe-driven strings.
  /// Never throws: missing key -> English table -> pretty fallback.
  String trDynamic(String key) {
    final norm = key.trim().toLowerCase().replaceAll(RegExp(r'\s+'), '_');
    final cur = _tables[code]?[norm];
    if (cur != null && cur.isNotEmpty) return cur;
    final en = _tables['en']?[norm];
    if (en != null && en.isNotEmpty) return en;
    return key.replaceAll('_', ' ');
  }
}