import '../../data/json_schedule_import.dart';
import 'school_navigation_policy.dart';

class UnsupportedSchoolLayout implements Exception {
  @override
  String toString() => '学校课表识别待联调，当前课表保持不变。';
}

class SchoolPageAdapter {
  ImportDraft extract(String html, Uri source) {
    // A real authenticated timetable fixture is required before registering a parser.
    // Unknown HTML must never erase the student's last valid imported timetable.
    throw UnsupportedSchoolLayout();
  }
}

class SchoolReader {
  SchoolReader(this.adapter);
  final SchoolPageAdapter adapter;
  Future<ImportDraft>? _pending;
  bool get busy => _pending != null;
  Future<ImportDraft> read(Uri origin, Future<String> Function() getHtml) {
    if (_pending != null) return _pending!;
    _pending = Future<ImportDraft>(() async {
      try {
        if (!SchoolNavigationPolicy.isTimetable(origin)) {
          throw UnsupportedSchoolLayout();
        }
        return adapter.extract(await getHtml(), origin);
      } finally {
        _pending = null;
      }
    });
    return _pending!;
  }
}