import 'dart:async';
import 'dart:convert';
import 'dart:typed_data';

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

/// An opt-in mail attachment, separate from persistent structured logs.
/// Keeps only course/exam evidence, never the surrounding account/login page.
class SchoolPageDiagnostic {
  SchoolPageDiagnostic({DateTime Function()? clock})
    : clock = clock ?? DateTime.now;
  static final instance = SchoolPageDiagnostic();
  static const maxBytes = 2 * 1024 * 1024;
  static const marker = '<!doctype html><!-- TPSchedule school diagnostic -->';
  final DateTime Function() clock;
  Uint8List? _bytes;
  DateTime? _at;
  Timer? _expiry;

  void clear() {
    _expiry?.cancel();
    _expiry = null;
    _bytes = null;
    _at = null;
  }

  Uint8List? export() {
    final at = _at;
    if (at == null ||
        clock().difference(at).isNegative ||
        clock().difference(at) >= const Duration(minutes: 10)) {
      clear();
    }
    return _bytes == null ? null : Uint8List.fromList(_bytes!);
  }

  void remember(String content, Uri uri) {
    clear();
    try {
      final undergraduate =
          uri.scheme == 'https' &&
          uri.port == 443 &&
          uri.host == 'eams.uestc.edu.cn' &&
          uri.path.startsWith('/eams/');
      final graduate =
          uri.host == 'yjsjy.uestc.edu.cn' &&
          (uri.scheme == 'https' && uri.port == 443 ||
              uri.scheme == 'http' && uri.port == 80) &&
          (uri.path == '/pyxx' || uri.path.startsWith('/pyxx/'));
      if ((!undergraduate && !graduate) ||
          uri.userInfo.isNotEmpty ||
          utf8.encode(content).length > maxBytes) {
        return;
      }
      final doc = html.parse(content);
      if (doc.querySelector('input[type="password"]') != null) return;
      final tables = doc
          .querySelectorAll('table')
          .where(
            (t) => graduate
                ? const ['tbl', 'sample-table-1'].contains(t.id)
                : t.id == 'manualArrangeCourseTable' ||
                      t.querySelector('tr')?.text.contains('课程序号') == true,
          )
          .toList();
      if (tables.isEmpty) return;
      final graduateTerms = <dom.Element>[];
      if (graduate) {
        for (final table in tables) {
          final id = table.id == 'tbl' ? 'drpxq' : 'xqbh';
          final original = doc.querySelector('select#$id');
          if (original == null) continue;
          final select = dom.Element.tag('select')..id = id;
          for (final originalOption in original.querySelectorAll('option')) {
            final option = dom.Element.tag('option')
              ..text = originalOption.text;
            final value = originalOption.attributes['value'];
            if (value != null && RegExp(r'^\d{1,6}$').hasMatch(value)) {
              option.attributes['value'] = value;
            }
            if (originalOption.attributes.containsKey('selected')) {
              option.attributes['selected'] = '';
            }
            select.children.add(option);
          }
          graduateTerms.add(select);
        }
      }
      final fields = <String, Set<String>>{};
      void field(String key, String value) {
        if (const ['semester.id', 'examType.id'].contains(key) &&
            RegExp(r'^\d{1,6}$').hasMatch(value)) {
          fields.putIfAbsent(key, () => {}).add(value);
        }
      }

      for (final input in doc.querySelectorAll('input')) {
        field(input.attributes['name'] ?? '', input.attributes['value'] ?? '');
      }
      for (final node in doc.querySelectorAll('script,input[name="params"]')) {
        final value = node.localName == 'input'
            ? node.attributes['value'] ?? ''
            : node.text;
        for (final m in RegExp(
          r'(semester\.id|examType\.id)=(\d{1,6})(?=[&"\x27\s]|$)',
        ).allMatches(value)) {
          field(m[1]!, m[2]!);
        }
      }
      final script = doc
          .querySelectorAll('script')
          .map((s) => s.text)
          .join('\n');
      // Only retain the literal course statements our parser reads. All other
      // scripts, URL-bearing attributes and form/account fields are omitted.
      final statements = undergraduate ? _courseStatements(script) : '';
      for (final table in tables) {
        for (final node in table.querySelectorAll(
          'script,style,link,iframe,object,embed,form,input,textarea,select,button,img,svg,video,audio,source,meta,base',
        )) {
          node.remove();
        }
        for (final node in [table, ...table.querySelectorAll('*')]) {
          final attrs = Map<String, String>.from(node.attributes);
          node.attributes.clear();
          final id = attrs['id'];
          if (node.localName == 'table' &&
              (id == 'manualArrangeCourseTable' ||
                  graduate && const ['tbl', 'sample-table-1'].contains(id))) {
            node.id = id!;
          } else if (graduate &&
              const ['td', 'th'].contains(node.localName) &&
              id != null &&
              RegExp(r'^t[0-7][13579]$').hasMatch(id)) {
            node.id = id;
          }
          for (final key in ['rowspan', 'colspan']) {
            final value = attrs[key];
            if (value != null && RegExp(r'^\d{1,2}$').hasMatch(value)) {
              node.attributes[key] = value;
            }
          }
        }
      }
      final safe =
          '$marker<html><head><meta charset="utf-8">'
          '<meta http-equiv="Content-Security-Policy" content="default-src \'none\'; base-uri \'none\'; form-action \'none\'">'
          '<title>TPSchedule school diagnostic</title></head><body>'
          '${graduateTerms.map((t) => t.outerHtml).join()}'
          '${fields.entries.expand((e) => e.value.map((v) => '<input type="hidden" name="${e.key}" value="$v">')).join()}'
          '${tables.map((t) => t.outerHtml).join()}'
          '<script type="application/x-tpschedule-course-data">${statements.replaceAll('<', r'\u003c')}</script></body></html>';
      final bytes = Uint8List.fromList(utf8.encode(safe));
      if (bytes.length > maxBytes) return;
      _bytes = bytes;
      _at = clock();
      _expiry = Timer(const Duration(minutes: 10), clear);
    } catch (_) {
      clear(); // Diagnostic collection must not interfere with importing.
    }
  }

  // Split outside quoted strings without validating the course arguments: a
  // malformed argument/index is precisely what this attachment must preserve.
  static String _courseStatements(String script) {
    final out = <String>[];
    var start = 0;
    String? quote;
    var lineComment = false, blockComment = false;
    final allowed = RegExp(
      r'^(?:var\s+)?(?:unitCount\s*=|activity\s*=\s*new\s+TaskActivity\b|new\s+TaskActivity\b|index\s*=|table\d+\.activities\s*\[)',
    );
    void keep(int end) {
      final statement = script
          .substring(start, end)
          .replaceFirst(
            RegExp(r'^(?:\s|//[^\r\n]*(?:\r?\n|$)|/\*[\s\S]*?\*/)*'),
            '',
          )
          .trim();
      if (allowed.hasMatch(statement)) out.add(statement);
      start = end;
    }

    for (var i = 0; i < script.length; i++) {
      final c = script[i];
      final next = i + 1 < script.length ? script[i + 1] : '';
      if (lineComment) {
        if (c == '\n' || c == '\r') lineComment = false;
      } else if (blockComment) {
        if (c == '*' && next == '/') {
          blockComment = false;
          i++;
        }
      } else if (quote != null) {
        if (c == '\\') {
          i++;
        } else if (c == quote) {
          quote = null;
        }
      } else if (c == '/' && next == '/') {
        lineComment = true;
        i++;
      } else if (c == '/' && next == '*') {
        blockComment = true;
        i++;
      } else if (c == '"' || c == "'" || c == '`') {
        quote = c;
      } else if (c == ';') {
        keep(i + 1);
      }
    }
    if (start < script.length) keep(script.length);
    return out.join('\n');
  }
}