import 'dart:async';

import 'package:flutter/foundation.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../../../core/database/app_database.dart';
import '../../data/repositories/food_search_repository.dart';
import '../../domain/entities/food_product.dart';
import '../../domain/repositories/food_search_repository.dart';

/// Application-wide food search repository (dual-source + drift cache).
///
/// Overridable in widget/unit tests with an in-memory fake.
final foodSearchRepositoryProvider = Provider<IFoodSearchRepository>(
  (ref) => FoodSearchRepository.defaults(ref.watch(appDatabaseProvider)),
);

/// Debounce applied to keystroke-driven searches.
const Duration kFoodSearchDebounce = Duration(milliseconds: 400);

/// Immutable snapshot of the food-search screen state.
class FoodSearchState {
  const FoodSearchState({
    this.query = '',
    this.products = const [],
    this.isSearching = false,
    this.errorMessage,
    this.hasSearched = false,
  });

  /// Active query text (kept in sync with the search field).
  final String query;

  /// Products matching [query] from the cache / Open Food Facts / USDA.
  final List<FoodProduct> products;

  /// Whether a lookup is currently in flight.
  final bool isSearching;

  /// Last lookup failure surfaced to the user; `null` when healthy.
  final String? errorMessage;

  /// Whether a lookup completed at least once (drives the empty state).
  final bool hasSearched;

  FoodSearchState copyWith({
    String? query,
    List<FoodProduct>? products,
    bool? isSearching,
    Object? errorMessage = _keep,
    bool? hasSearched,
  }) =>
      FoodSearchState(
        query: query ?? this.query,
        products: products ?? this.products,
        isSearching: isSearching ?? this.isSearching,
        errorMessage: identical(errorMessage, _keep)
            ? this.errorMessage
            : errorMessage as String?,
        hasSearched: hasSearched ?? this.hasSearched,
      );

  /// Sentinel allowing `copyWith` to explicitly reset a field to `null`.
  static const Object _keep = Object();
}

/// Orchestrates the food search flow: debounced text queries, direct barcode
/// lookups, and the loading/error states consumed by [FoodSearchScreen].
///
/// Supersedes in-flight lookups via a monotonically increasing request token
/// so a slow cache/network response can never overwrite a newer query.
class FoodSearchController extends StateNotifier<FoodSearchState> {
  FoodSearchController(this._repository) : super(const FoodSearchState());

  final IFoodSearchRepository _repository;

  Timer? _debounce;
  int _requestToken = 0;

  @override
  void dispose() {
    _debounce?.cancel();
    super.dispose();
  }

  /// Updates the query text and schedules a debounced lookup.
  void onQueryChanged(String query) {
    _debounce?.cancel();
    final trimmed = query.trim();

    if (trimmed.isEmpty) {
      state = FoodSearchState(query: query);
      return;
    }

    state = state.copyWith(query: query, isSearching: true, errorMessage: null);
    _debounce = Timer(kFoodSearchDebounce, () => _runTextSearch(trimmed));
  }

  /// Immediately resolves [barcode] (UPC/EAN from the scanner or manual
  /// entry), bypassing the debounce.
  Future<void> lookupBarcode(String barcode) async {
    final trimmed = barcode.trim();
    if (trimmed.isEmpty) return;

    _debounce?.cancel();
    state = state.copyWith(
      query: trimmed,
      isSearching: true,
      errorMessage: null,
    );

    final token = ++_requestToken;
    try {
      final results = await _repository.lookupBarcode(trimmed);
      if (!_isCurrent(token)) return;
      state = state.copyWith(
        products: results,
        isSearching: false,
        hasSearched: true,
        errorMessage: results.isEmpty
            ? 'No product found for "$trimmed".'
            : null,
      );
    } catch (error, stackTrace) {
      if (!_isCurrent(token)) return;
      _recordError(error, stackTrace, 'barcode lookup failed');
    }
  }

  /// Clears the query and results (search-bar "x" button).
  void clear() {
    _debounce?.cancel();
    _requestToken++;
    state = const FoodSearchState();
  }

  /// Re-runs the current query immediately (error-state retry / manual
  /// refresh).
  Future<void> retry() async {
    final query = state.query.trim();
    if (query.isEmpty) return;
    if (_looksLikeBarcode(query)) {
      await lookupBarcode(query);
    } else {
      await _runTextSearch(query);
    }
  }

  Future<void> _runTextSearch(String query) async {
    final token = ++_requestToken;
    state = state.copyWith(isSearching: true, errorMessage: null);
    try {
      final results = await _repository.searchByText(query);
      if (!_isCurrent(token)) return;
      state = state.copyWith(
        products: results,
        isSearching: false,
        hasSearched: true,
      );
    } catch (error, stackTrace) {
      if (!_isCurrent(token)) return;
      _recordError(error, stackTrace, 'text search failed');
    }
  }

  bool _isCurrent(int token) => token == _requestToken && mounted;

  /// UPC-A/EAN-8/13/14 detection used to route typed queries through the
  /// barcode path.
  static bool _looksLikeBarcode(String query) =>
      RegExp(r'^\d{8}$|^\d{12,14}$').hasMatch(query);

  void _recordError(Object error, StackTrace stackTrace, String label) {
    debugPrintStack(stackTrace: stackTrace, label: '$label failed');
    state = state.copyWith(
      products: const [],
      isSearching: false,
      hasSearched: true,
      errorMessage: 'Search failed. Check your connection and try again.',
    );
  }
}

/// Exposes the [FoodSearchController] to the widget tree.
final foodSearchControllerProvider =
    StateNotifierProvider<FoodSearchController, FoodSearchState>(
  (ref) => FoodSearchController(ref.watch(foodSearchRepositoryProvider)),
);