import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../core/auth/auth_provider.dart';
import '../../shared/models/diary_entry.dart';
import '../../shared/models/menu.dart';
import '../../shared/models/shopping_item.dart';
import 'menu_service.dart';

// ── Service provider ──────────────────────────────────────────

final menuServiceProvider = Provider<MenuService>((ref) {
  return MenuService(ref.read(apiClientProvider));
});

// ── Current week (state) ──────────────────────────────────────

/// The ISO week string for the currently displayed week, e.g. "2026-W08".
final currentWeekProvider = StateProvider<String>((ref) {
  final now = DateTime.now().toUtc();
  final (y, w) = _isoWeek(now);
  return '$y-W${w.toString().padLeft(2, '0')}';
});

(int year, int week) _isoWeek(DateTime dt) {
  // Shift to Thursday to get ISO week year.
  final thu = dt.add(Duration(days: 4 - (dt.weekday == 7 ? 0 : dt.weekday)));
  final jan1 = DateTime.utc(thu.year, 1, 1);
  final week = ((thu.difference(jan1).inDays) / 7).ceil();
  return (thu.year, week);
}

/// Returns the ISO 8601 week string for [date], e.g. "2026-W12".
String isoWeekString(DateTime date) {
  final (year, week) = _isoWeek(date.toUtc());
  return '$year-W${week.toString().padLeft(2, '0')}';
}

// ── Menu notifier ─────────────────────────────────────────────

class MenuNotifier extends StateNotifier<AsyncValue<MenuPlan?>> {
  final MenuService _service;
  final String _week;

  MenuNotifier(this._service, this._week) : super(const AsyncValue.loading()) {
    load();
  }

  Future<void> load() async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() => _service.getMenu(week: _week));
  }

  Future<void> generate() async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() => _service.generateMenu(week: _week));
  }

  Future<void> updateItem(String itemId, String recipeId) async {
    await _service.updateMenuItem(itemId, recipeId);
    await load();
  }

  Future<void> deleteItem(String itemId) async {
    await _service.deleteMenuItem(itemId);
    await load();
  }
}

final menuProvider =
    StateNotifierProvider.family<MenuNotifier, AsyncValue<MenuPlan?>, String>(
  (ref, week) => MenuNotifier(ref.read(menuServiceProvider), week),
);

// ── Shopping list notifier ────────────────────────────────────

class ShoppingListNotifier extends StateNotifier<AsyncValue<List<ShoppingItem>>> {
  final MenuService _service;
  final String _week;

  ShoppingListNotifier(this._service, this._week)
      : super(const AsyncValue.loading()) {
    load();
  }

  Future<void> load() async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() => _service.getShoppingList(week: _week));
  }

  Future<void> regenerate() async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(
        () => _service.generateShoppingList(week: _week));
  }

  Future<void> toggle(int index, bool checked) async {
    // Optimistic update.
    state = state.whenData((items) {
      final list = List<ShoppingItem>.from(items);
      if (index < list.length) {
        list[index] = list[index].copyWith(checked: checked);
      }
      return list;
    });
    try {
      await _service.toggleShoppingItem(index, checked, week: _week);
    } catch (_) {
      // Revert on failure.
      await load();
    }
  }
}

final shoppingListProvider = StateNotifierProvider.family<
    ShoppingListNotifier, AsyncValue<List<ShoppingItem>>, String>(
  (ref, week) => ShoppingListNotifier(ref.read(menuServiceProvider), week),
);

// ── Diary notifier ────────────────────────────────────────────

class DiaryNotifier extends StateNotifier<AsyncValue<List<DiaryEntry>>> {
  final MenuService _service;
  final String _date;

  DiaryNotifier(this._service, this._date) : super(const AsyncValue.loading()) {
    load();
  }

  Future<void> load() async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() => _service.getDiary(_date));
  }

  Future<void> add(Map<String, dynamic> body) async {
    await _service.createDiaryEntry(body);
    await load();
  }

  Future<void> remove(String id) async {
    final prev = state;
    state = state.whenData((l) => l.where((e) => e.id != id).toList());
    try {
      await _service.deleteDiaryEntry(id);
    } catch (_) {
      state = prev;
    }
  }
}

final diaryProvider =
    StateNotifierProvider.family<DiaryNotifier, AsyncValue<List<DiaryEntry>>, String>(
  (ref, date) => DiaryNotifier(ref.read(menuServiceProvider), date),
);

// ── Plan menu helpers ─────────────────────────────────────────

/// The latest future date (among cached menus for the current and next two weeks)
/// that already has at least one planned meal slot. Returns null when no future
/// meals are planned.
final lastPlannedDateProvider = Provider<DateTime?>((ref) {
  final today = DateTime.now();
  DateTime? latestDate;
  for (var offsetDays = 0; offsetDays <= 14; offsetDays += 7) {
    final weekDate = today.add(Duration(days: offsetDays));
    final plan = ref.watch(menuProvider(isoWeekString(weekDate))).valueOrNull;
    if (plan == null) continue;
    for (final day in plan.days) {
      final dayDate = DateTime.parse(day.date);
      if (dayDate.isAfter(today) && day.meals.isNotEmpty) {
        if (latestDate == null || dayDate.isAfter(latestDate)) {
          latestDate = dayDate;
        }
      }
    }
  }
  return latestDate;
});

/// Service for planning meals across specific dates.
/// Calls the API and then invalidates the affected week providers so that
/// [plannedMealsProvider] picks up the new slots automatically.
class PlanMenuService {
  final Ref _ref;

  const PlanMenuService(this._ref);

  Future<void> generateForDates({
    required List<String> dates,
    required List<String> mealTypes,
  }) async {
    final menuService = _ref.read(menuServiceProvider);
    final plans = await menuService.generateForDates(
      dates: dates,
      mealTypes: mealTypes,
    );
    for (final plan in plans) {
      _ref.invalidate(menuProvider(isoWeekString(DateTime.parse(plan.weekStart))));
    }
  }
}

final planMenuServiceProvider = Provider<PlanMenuService>((ref) {
  return PlanMenuService(ref);
});