import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:timezone/timezone.dart' as tz;

/// Single source of truth for time-zone display prefs (v1: local-only).
/// Mirrors LocaleProvider: ChangeNotifier + SharedPreferences + notifyListeners.
/// Backend sync (AppUser.multitime) is a later phase; for now prefs stay on-device
/// so the settings card in the screenshot works standalone + multilingual.
class TimezoneProvider with ChangeNotifier {
  static const _zoneKey = 'app_timezone_id';
  static const _patternKey = 'app_date_pattern';
  static const _is24hKey = 'app_time_24h';
  static const _weekStartKey = 'app_week_start';

  /// Curated quick-pick list matching the settings mock.
  static const commonZoneIds = [
    'Asia/Kolkata',
    'Asia/Dubai',
    'Asia/Singapore',
    'Asia/Kuala_Lumpur',
    'Asia/Hong_Kong',
    'Asia/Shanghai',
    'Asia/Taipei',
    'Asia/Tokyo',
    'Asia/Seoul',
    'Asia/Bangkok',
    'Asia/Jakarta',
    'Asia/Manila',
    'Asia/Karachi',
    'Europe/London',
    'Europe/Paris',
    'Europe/Berlin',
    'America/New_York',
    'America/Chicago',
    'America/Denver',
    'America/Los_Angeles',
    'America/Toronto',
    'Australia/Sydney',
    'UTC',
  ];

  static const datePatterns = ['dd-MM-yyyy', 'MM-dd-yyyy', 'yyyy-MM-dd'];
  static const weekDays = [
    'Monday',
    'Tuesday',
    'Wednesday',
    'Thursday',
    'Friday',
    'Saturday',
    'Sunday',
  ];

  String _zoneId = 'Asia/Kolkata';
  String get zoneId => _zoneId;

  String _datePattern = 'dd-MM-yyyy';
  String get datePattern => _datePattern;

  bool _is24h = true;
  bool get is24h => _is24h;

  String _weekStart = 'Monday';
  String get weekStart => _weekStart;

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

  /// Short city label: 'Asia/Kolkata' -> 'Kolkata', 'UTC' -> 'UTC'.
  static String cityOf(String id) {
    if (id == 'UTC') return 'UTC';
    final parts = id.split('/');
    final raw = parts.isNotEmpty ? parts.last : id;
    return raw.replaceAll('_', ' ');
  }

  Future<void> init() async {
    final prefs = await SharedPreferences.getInstance();
    final z = prefs.getString(_zoneKey);
    if (z != null && z.isNotEmpty) _zoneId = z;
    final p = prefs.getString(_patternKey);
    if (p != null && datePatterns.contains(p)) _datePattern = p;
    final h = prefs.getBool(_is24hKey);
    if (h != null) _is24h = h;
    final w = prefs.getString(_weekStartKey);
    if (w != null && weekDays.contains(w)) _weekStart = w;
    _ready = true;
    notifyListeners();
  }

  Future<void> setZone(String id) async {
    _zoneId = id;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_zoneKey, id);
    notifyListeners();
  }

  Future<void> setDatePattern(String p) async {
    if (!datePatterns.contains(p)) return;
    _datePattern = p;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_patternKey, p);
    notifyListeners();
  }

  Future<void> setIs24h(bool v) async {
    _is24h = v;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setBool(_is24hKey, v);
    notifyListeners();
  }

  Future<void> setWeekStart(String d) async {
    if (!weekDays.contains(d)) return;
    _weekStart = d;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_weekStartKey, d);
    notifyListeners();
  }

  /// Explicit save (button in the mock). Values are already persisted on
  /// change; this re-persists + notifies so callers can show a snackbar.
  Future<void> save() async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_zoneKey, _zoneId);
    await prefs.setString(_patternKey, _datePattern);
    await prefs.setBool(_is24hKey, _is24h);
    await prefs.setString(_weekStartKey, _weekStart);
    notifyListeners();
  }

  tz.Location get location {
    try {
      return tz.getLocation(_zoneId);
    } catch (_) {
      return tz.getLocation('UTC');
    }
  }

  tz.TZDateTime nowInZone() {
    try {
      return tz.TZDateTime.now(location);
    } catch (_) {
      return tz.TZDateTime.now(tz.getLocation('UTC'));
    }
  }

  /// e.g. 'GMT+5:30', 'GMT-4:00', 'GMT'. DST-aware via timezone DB.
  String offsetLabel([tz.TZDateTime? at]) {
    try {
      final dt = at ?? nowInZone();
      final offset = dt.timeZoneOffset;
      if (offset == Duration.zero) return 'GMT';
      final sign = offset.isNegative ? '-' : '+';
      final abs = offset.abs();
      final h = abs.inHours.toString();
      final m = (abs.inMinutes % 60).toString().padLeft(2, '0');
      return 'GMT$sign$h:$m';
    } catch (_) {
      return '';
    }
  }

  /// 'Kolkata (GMT+5:30)' style label for dropdown rows.
  String displayLabel(String id) {
    try {
      final loc = tz.getLocation(id);
      final now = tz.TZDateTime.now(loc);
      final offset = now.timeZoneOffset;
      final sign = offset.isNegative ? '-' : '+';
      final abs = offset.abs();
      final off = offset == Duration.zero
          ? 'GMT'
          : 'GMT$sign${abs.inHours}:${(abs.inMinutes % 60).toString().padLeft(2, '0')}';
      return '${cityOf(id)} ($off)';
    } catch (_) {
      return cityOf(id);
    }
  }
}