import 'dart:convert';

import 'package:html/parser.dart' as html;

import '../../domain/exam_schedule.dart';

class SchoolExamAdapter {
  static ExamSchedule extract(String content) {
    try {
      if (utf8.encode(content).length > 2 * 1024 * 1024) {
        throw const FormatException();
      }
      final document = html.parse(content);
      final selected = document.querySelector('#xqbh option[selected]');
      final term = selected?.attributes['value'];
      final table = document.querySelector('#sample-table-1');
      const headers = [
        'id',
        '序号',
        '学号',
        '姓名',
        '课程代码',
        '课程名称',
        '考核方式',
        '考生编号',
        '考场顺序号',
        '考场',
        '座位号',
        '考试时间',
      ];
      if (selected == null ||
          term == null ||
          table == null ||
          !RegExp(r'^\d+$').hasMatch(term)) {
        throw const FormatException();
      }
      final rows = table.querySelectorAll('tr');
      if (rows.isEmpty || rows.first.children.length != headers.length) {
        throw const FormatException();
      }
      for (var i = 0; i < headers.length; i++) {
        if (rows.first.children[i].text.trim() != headers[i]) {
          throw const FormatException();
        }
      }
      final records = <ExamRecord>[];
      var explicitlyEmpty = false;
      for (final row in rows.skip(1)) {
        // DataTables can insert a single explicit no-data placeholder.
        if (row.children.length == 1 &&
            row.children.first.attributes['colspan'] == '12' &&
            const [
              '没有数据',
              '暂无数据',
              '无数据',
              'No data available in table',
            ].contains(row.text.trim())) {
          explicitlyEmpty = true;
          continue;
        }
        if (row.children.length != 12 ||
            row.querySelector('script,style') != null) {
          throw const FormatException();
        }
        final cells = row.children.map((c) => c.text.trim()).toList();
        records.add(
          ExamRecord(
            code: cells[4],
            name: cells[5],
            assessment: cells[6],
            candidate: cells[7],
            sequence: cells[8],
            room: cells[9],
            seat: cells[10],
            time: cells[11],
          ),
        );
      }
      if (records.isEmpty && !explicitlyEmpty) throw const FormatException();
      return ExamSchedule.fromJson(
        ExamSchedule(
          semesterLabel: selected.text.trim(),
          termId: term,
          records: records,
        ).toJson(),
      );
    } catch (_) {
      throw const FormatException('未识别到完整的考试查询表，已有考试信息保持不变。');
    }
  }
}