import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../../../app/providers.dart';
import '../../../domain/entities/store_account.dart';

/// Sign-in state for the terminal.
sealed class AuthState {
  const AuthState();

  bool get isAuthenticated => this is Authenticated;
}

class Unauthenticated extends AuthState {
  const Unauthenticated();
}

class Authenticating extends AuthState {
  const Authenticating();
}

class Authenticated extends AuthState {
  const Authenticated({required this.store, required this.user});

  final StoreAccount store;
  final StaffUser user;
}

class AuthFailure extends AuthState {
  const AuthFailure(this.message);

  final String message;
}

/// Store-level credentials for the unregistered build.
///
/// Still a constant, and deliberately so: this is the *store* login, not a
/// person's, and it is replaced wholesale when the terminal is registered
/// against a real back office. Staff PINs — the credential that actually opens
/// a till drawer — are no longer here. They live hashed in the database.
class DemoCredentials {
  const DemoCredentials._();

  static const String email = 'admin@nearle.in';
  static const String password = 'nearle123';
}

/// Validates store credentials and holds the signed-in session.
class AuthController extends StateNotifier<AuthState> {
  AuthController(this._ref) : super(const Unauthenticated());

  final Ref _ref;

  Future<bool> signIn({
    required String email,
    required String password,
  }) async {
    state = const Authenticating();

    // Stand-in for the network round trip.
    await Future<void>.delayed(const Duration(milliseconds: 600));

    final normalised = email.trim().toLowerCase();

    if (normalised != DemoCredentials.email) {
      state = const AuthFailure('No store is registered against that email.');
      return false;
    }

    if (password != DemoCredentials.password) {
      state = const AuthFailure('Incorrect password. Please try again.');
      return false;
    }

    final store = await _ref.read(storeAccountProvider.future);
    final staff = store.staff;

    if (staff.isEmpty) {
      state = const AuthFailure(
        'This terminal has no staff accounts. Reinstall to seed them.',
      );
      return false;
    }

    // The first admin, or whoever is there. A person switches to their own
    // account at the till.
    final opener = staff.firstWhere(
      (s) => s.role == StaffRole.admin,
      orElse: () => staff.first,
    );

    state = Authenticated(store: store, user: opener);
    return true;
  }

  /// Switches the active operator, checking their PIN.
  ///
  /// Every bill is stamped with whoever is active, so this is the boundary that
  /// decides who a sale is attributed to — it cannot be a bare selection from a
  /// list.
  Future<bool> switchUser(String pin) async {
    final current = state;
    if (current is! Authenticated) return false;

    final store = _ref.read(localStoreProvider);
    final user = await store.staff.authenticate(pin);
    if (user == null) return false;

    state = Authenticated(store: current.store, user: user);
    return true;
  }

  /// Re-reads the store after staff or details change, keeping the session.
  Future<void> refreshStore() async {
    final current = state;
    if (current is! Authenticated) return;

    _ref.invalidate(storeAccountProvider);
    final store = await _ref.read(storeAccountProvider.future);

    final me = store.staff.where((s) => s.id == current.user.id);
    state = Authenticated(
      store: store,
      // Signed out if the active operator was just deactivated — carrying on
      // would keep stamping bills with an account the shop has revoked.
      user: me.isEmpty ? store.staff.first : me.first,
    );
  }

  void signOut() => state = const Unauthenticated();

  void clearError() {
    if (state is AuthFailure) state = const Unauthenticated();
  }
}

final authControllerProvider = StateNotifierProvider<AuthController, AuthState>(
  AuthController.new,
);

/// The signed-in store, or null before sign-in.
final currentStoreProvider = Provider<StoreAccount?>((ref) {
  final s = ref.watch(authControllerProvider);
  return s is Authenticated ? s.store : null;
});

/// The active operator, or null before sign-in.
final currentUserProvider = Provider<StaffUser?>((ref) {
  final s = ref.watch(authControllerProvider);
  return s is Authenticated ? s.user : null;
});

/// True while anyone is still on a seeded or admin-reset PIN.
final mustChangePinProvider = Provider<bool>((ref) {
  final user = ref.watch(currentUserProvider);
  return user?.mustChangePin ?? false;
});