import 'dart:async';

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

import 'api.dart';

enum SessionState { checking, signedOut, admin }

/// Who is signed in. Only admin accounts get past the sign-in page: anyone else is
/// signed straight out again (the database refuses their changes either way).
class AdminSession extends ChangeNotifier {
  AdminSession._();
  static final instance = AdminSession._();

  SessionState state = SessionState.checking;
  String? email;

  /// Shown on the sign-in page after a non-admin account tried to sign in.
  String? refusal;

  StreamSubscription<AuthState>? _sub;

  void start() {
    _sub ??= Supabase.instance.client.auth.onAuthStateChange.listen((e) => _check(e.session));
    _check(Supabase.instance.client.auth.currentSession);
  }

  Future<void> _check(Session? session) async {
    if (session == null) {
      _set(SessionState.signedOut, null);
      return;
    }
    if (state == SessionState.admin && email == session.user.email) return;
    try {
      if (await AdminApi.isAdmin()) {
        refusal = null;
        _set(SessionState.admin, session.user.email);
        return;
      }
      refusal = '${session.user.email} is not an admin account.';
    } catch (e) {
      refusal = 'Could not check your account: $e';
    }
    await AdminApi.signOut();
    _set(SessionState.signedOut, null);
  }

  void _set(SessionState s, String? e) {
    if (s == state && e == email) return;
    state = s;
    email = e;
    notifyListeners();
  }
}