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,
    required this.login,
  });

  final StoreAccount store;
  final StaffUser user;

  /// Which credential opened this session. The authority on what the terminal
  /// is allowed to show — not [user], which can be swapped at the till.
  final TerminalLogin login;

  StaffRole get role => login.role;

  bool get isAdmin => login == TerminalLogin.admin;
  bool get isCashier => login == TerminalLogin.cashier;
}

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

  final String message;
}

/// The two ways into this terminal.
///
/// Store-level credentials, not a person's: they are replaced wholesale when
/// the terminal is registered against a real back office. Staff PINs — the
/// credential that actually opens a till drawer — are not here. They live
/// hashed in the database.
///
/// The split is what the two roles are *for*, not decoration:
///
/// * [admin] runs the whole shell and is the only login that can pull the
///   catalogue. Signing out leaves the products on the terminal.
/// * [cashier] gets the billing screen and nothing else, and signing out
///   takes the catalogue with it.
enum TerminalLogin {
  admin(
    label: 'Admin',
    email: 'admin@nearle.in',
    password: 'nearle123',
    role: StaffRole.admin,
    blurb: 'Full shell — import products, promos, settings.',
  ),
  cashier(
    label: 'Cashier',
    email: 'cashier@nearle.in',
    password: 'cashier123',
    role: StaffRole.cashier,
    blurb: 'Billing only, on the products the admin imported.',
  );

  const TerminalLogin({
    required this.label,
    required this.email,
    required this.password,
    required this.role,
    required this.blurb,
  });

  final String label;
  final String email;
  final String password;
  final StaffRole role;
  final String blurb;

  /// The catalogue is pulled once by an admin and billed against by whoever is
  /// on the counter, so only the cashier's sign-out drops it. An admin closing
  /// the shell is a handover, not the end of the day.
  bool get clearsCatalogueOnSignOut => this == TerminalLogin.cashier;

  static TerminalLogin? byEmail(String email) {
    final normalised = email.trim().toLowerCase();
    for (final login in TerminalLogin.values) {
      if (login.email == normalised) return login;
    }
    return null;
  }
}

/// Kept for the store record, which is keyed on the outlet's own address.
class DemoCredentials {
  const DemoCredentials._();

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

  static const String cashierEmail = 'cashier@nearle.in';
  static const String cashierPassword = 'cashier123';
}

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

  final Ref _ref;

  /// Whether signing out right now would wipe the products off this terminal.
  ///
  /// Read *before* [signOut] by anything that needs to warn the operator, since
  /// the session is gone by the time it returns.
  bool get clearsCatalogueOnSignOut {
    final current = state;
    return current is Authenticated && current.login.clearsCatalogueOnSignOut;
  }

  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 login = TerminalLogin.byEmail(email);

    if (login == null) {
      state = const AuthFailure('No account is registered against that email.');
      return false;
    }

    if (password != login.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;
    }

    // Whoever on this terminal matches the role that just signed in. Falls
    // back rather than failing: the session's permissions come from [login],
    // so a shop with no cashier row still gets a usable till — the bills are
    // just stamped with the account that is there.
    final opener = staff.firstWhere(
      (s) => s.role == login.role,
      orElse: () => staff.first,
    );

    state = Authenticated(store: store, user: opener, login: login);
    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. It changes who the bill names, never what the session may open:
  /// [Authenticated.login] is untouched, so a cashier terminal stays a cashier
  /// terminal.
  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,
      login: current.login,
    );
    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,
      login: current.login,
    );
  }

  /// Ends the session, and — for a cashier only — the catalogue with it.
  ///
  /// Every cashier sign-out drops the products, whatever the reason for it.
  /// The next shift should bill against what the back office answers with,
  /// never a catalogue carried over, and a terminal left at a login screen
  /// must not be sitting on a shop's prices and stock.
  ///
  /// An admin signing out is the opposite case. They have just pulled the
  /// products *so that* a cashier can pick the terminal up, so dropping the
  /// table here would make the import pointless.
  Future<void> signOut() async {
    if (clearsCatalogueOnSignOut) {
      await _ref.read(localStoreProvider).clearCatalogue();
    }
    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;
});

/// Which credential is holding this session open, or null before sign-in.
final terminalLoginProvider = Provider<TerminalLogin?>((ref) {
  final s = ref.watch(authControllerProvider);
  return s is Authenticated ? s.login : null;
});

/// True when the terminal is locked down to the billing screen.
///
/// The one flag the shell reads: no sidebar, no back-office modules, sign-out
/// and events promoted to the header.
final isCashierModeProvider = Provider<bool>(
  (ref) => ref.watch(terminalLoginProvider) == TerminalLogin.cashier,
);

final isAdminModeProvider = Provider<bool>(
  (ref) => ref.watch(terminalLoginProvider) == TerminalLogin.admin,
);

/// 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;
});