import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';
import 'package:new_learn/core/storage/stores/answer_record_store.dart';
import 'package:new_learn/features/exam/answer_provider.dart';
import 'package:new_learn/features/exam/answer_sheet_dialog.dart';
import 'package:new_learn/features/exam/exam_question.dart';
import 'package:new_learn/features/exam/paper_provider.dart';
import 'package:new_learn/features/exam/question_card.dart';
import 'package:new_learn/features/exam/question_type.dart';

/// ============================================================
/// 【ExamPage】试卷练习页 —— 大数据滑动核心 Demo
///
/// 一、组件协作（本页是唯一桥接 Riverpod 的地方）：
///   paperProvider   → `AsyncValue<List<Question>>`：loading/error/data 三态
///   answerProvider  → `Map<int, String>`：当前全部答案，ref.watch 响应式
///   QuestionCard    → 纯展示组件，props 传题 + 答案 + 作答回调
///
/// 二、PageView.builder 大数据性能（对应 Vue3 swiper 方案分析）：
///   - builder 惰性构建：只构建视口内 ±1 页（cacheExtent），
///     100 道题传入也只是个 List，滑出的页面 Element 自动回收；
///   - allowImplicitScrolling: true → 预构建相邻页，滑动不掉帧；
///   - ValueKey(questionId) → 页面复用时按题号隔离，杜绝串题。
///
/// 三、续答链路（进卷 → 作答 → 交卷）：
///   进卷  initState → AnswerRecordStore.findByPaper 读回 →
///         注入 answerProvider（有记录则 SnackBar 提示已恢复）；
///   作答  QuestionCard 回调 → answer() 更新内存 + 异步写 Isar；
///   交卷  确认 → 判分统计 → deleteByPaper 清理 → clear 内存。
///
/// 四、坑：
///   1. restore 是异步的，首次 build 时答案可能还没回来 →
///      注入后 provider 变化自动重建页面（响应式），无需手动刷新；
///   2. 交卷接口失败不能删本地记录（防"没交成但答案没了"），
///      本 Demo 模拟提交成功后统一清理。
/// ============================================================
class ExamPage extends ConsumerStatefulWidget {
  const ExamPage({super.key});

  @override
  ConsumerState<ExamPage> createState() => _ExamPageState();
}

class _ExamPageState extends ConsumerState<ExamPage> {
  final PageController _pageController = PageController();
  int _currentIndex = 0;

  /// 续答恢复后要定位到的题号（null = 不跳转，只定位一次）
  int? _jumpToQuestion;

  @override
  void initState() {
    super.initState();
    _restoreProgress();
  }

  @override
  void dispose() {
    _pageController.dispose();
    super.dispose();
  }

  /// 【进卷恢复】从 Isar 读回本卷已答记录 → 注入 answerProvider
  /// 并定位到最后作答的题（按 updatedAt 最新一条）。
  ///
  /// 为什么还要定位：恢复的只是"答案数据"，PageView 初始还在第 1 题，
  /// 不定位的话用户每次进卷都要手动滑回上次位置（本 Bug 修复点）。
  Future<void> _restoreProgress() async {
    final records = await AnswerRecordStore.instance.findByPaper(demoPaperId);
    if (!mounted || records.isEmpty) return;
    final saved = <int, String>{};
    int? lastQuestionId;
    DateTime? lastAt;
    for (final r in records) {
      final qid = r.questionId as int;
      saved[qid] = (r.answer as String?) ?? '';
      // 记录最后作答的题：updatedAt 最新的一条（重复作答会覆盖更新时间）
      final at = r.updatedAt as DateTime?;
      if (at != null && (lastAt == null || at.isAfter(lastAt))) {
        lastAt = at;
        lastQuestionId = qid;
      }
    }
    ref.read(answerProvider.notifier).restore(saved);
    _jumpToQuestion = lastQuestionId;
    _tryJumpAfterRestore(); // 若题目已加载完成（异步竞争），这里直接跳
    if (!mounted) return;
    ScaffoldMessenger.of(context)
      ..hideCurrentSnackBar()
      ..showSnackBar(
        SnackBar(
          content: Text('已恢复上次答题进度（${saved.length} 题），定位到第 $lastQuestionId 题'),
          duration: const Duration(seconds: 2),
        ),
      );
  }

  /// 定位到最后作答的题：restore 与题目加载谁先完成都能跳转
  void _tryJumpAfterRestore() {
    final target = _jumpToQuestion;
    if (target == null) return;
    final questions = ref.read(paperProvider).value;
    if (questions == null) return; // 题目还没加载完，等 build data 分支再试
    final index = questions.indexWhere((q) => q.questionId == target);
    if (index < 0) return;
    _jumpToQuestion = null; // 只定位一次
    WidgetsBinding.instance.addPostFrameCallback((_) {
      // 首帧后跳转：此时 PageView 已 attach，jumpToPage 才安全
      if (!mounted || !_pageController.hasClients) return;
      _pageController.jumpToPage(index);
    });
  }

  /// 【交卷】确认 → 清理本地进度 → 判分统计
  Future<void> _submit(List<ExamQuestion> questions) async {
    final answers = ref.read(answerProvider);
    final total = questions.length;
    final answered =
        questions.where((q) => (answers[q.questionId] ?? '').isNotEmpty).length;

    final confirmed = await showDialog<bool>(
      context: context,
      builder: (ctx) => AlertDialog(
        title: const Text('确认交卷？'),
        content: Text('已答 $answered / $total 题，未答 ${total - answered} 题。'),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(ctx, false),
            child: const Text('再检查一下'),
          ),
          FilledButton(
            onPressed: () => Navigator.pop(ctx, true),
            child: const Text('交卷'),
          ),
        ],
      ),
    );
    if (confirmed != true || !mounted) return;

    // 模拟提交接口成功 → 清理本地进度（防止下次进卷恢复旧答案）
    await AnswerRecordStore.instance.deleteByPaper(demoPaperId);
    ref.read(answerProvider.notifier).clear();
    if (!mounted) return;

    // 判分：选择/判断自动比对；解答题不算分（需人工批改）
    final rightCount = questions.where((q) {
      if (q.type == QuestionType.essay) return false; // 解答题跳过
      final user = answers[q.questionId];
      return user != null && user == q.answer;
    }).length;

    if (!mounted) return;
    await showDialog<void>(
      context: context,
      builder: (ctx) => AlertDialog(
        title: const Text('交卷成功'),
        content: Text(
          '自动判分：答对 $rightCount / ${total - answered} 题（客观题）\n'
          '主观题需人工批改，本地进度已清理，下次进卷重新作答。',
        ),
        actions: [
          FilledButton(
            onPressed: () => Navigator.pop(ctx),
            child: const Text('知道了'),
          ),
        ],
      ),
    );
  }

  /// 打开答题卡
  void _openAnswerSheet(List<ExamQuestion> questions) {
    showDialog<void>(
      context: context,
      builder: (ctx) => AnswerSheetDialog(
        questionIds: [for (final q in questions) q.questionId],
        answers: ref.read(answerProvider),
        currentIndex: _currentIndex,
        onJump: (index) {
          Navigator.pop(ctx);
          _pageController.jumpToPage(index);
        },
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    final paperAsync = ref.watch(paperProvider);
    final answers = ref.watch(answerProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('试卷练习'),
        actions: [
          TextButton(
            onPressed: paperAsync.hasValue
                ? () => _submit(paperAsync.value!)
                : null,
            child: const Text(
              '交卷',
              style: TextStyle(fontWeight: FontWeight.w600),
            ),
          ),
        ],
      ),
      body: paperAsync.when(
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (e, _) => Center(
          child: Text('试卷加载失败：$e', style: const TextStyle(fontSize: 14)),
        ),
        data: (questions) {
          // 续答恢复可能晚于题目加载完成：data 分支兜底再触发一次定位
          _tryJumpAfterRestore();
          return Column(
            children: [
              _buildProgressBar(questions, answers),
              Expanded(
                child: PageView.builder(
                  controller: _pageController,
                  itemCount: questions.length,
                  // 预构建相邻页：滑动时目标页已就绪，不掉帧
                  allowImplicitScrolling: true,
                  onPageChanged: (i) => setState(() => _currentIndex = i),
                  itemBuilder: (context, i) {
                    final q = questions[i];
                    return QuestionCard(
                      // 按题号隔离：PageView 页面复用时杜绝串题
                      key: ValueKey(q.questionId),
                      question: q,
                      answer: answers[q.questionId],
                      onAnswer: (v) =>
                          ref.read(answerProvider.notifier).answer(q.questionId, v),
                    );
                  },
                ),
              ),
              _buildBottomBar(questions),
            ],
          );
        },
      ),
    );
  }

  /// 顶部进度条：已答 X / N + 当前题号
  Widget _buildProgressBar(List<ExamQuestion> questions, Map<int, String> answers) {
    final total = questions.length;
    final answered =
        questions.where((q) => (answers[q.questionId] ?? '').isNotEmpty).length;
    return Container(
      padding: EdgeInsets.fromLTRB(16.w, 12.h, 16.w, 10.h),
      color: Colors.white,
      child: Column(
        children: [
          Row(
            children: [
              Text(
                '第 ${_currentIndex + 1} / $total 题',
                style: TextStyle(
                  fontSize: 13.sp,
                  fontWeight: FontWeight.w600,
                  color: const Color(0xFF333333),
                ),
              ),
              const Spacer(),
              Text(
                '已答 $answered 题',
                style: TextStyle(fontSize: 12.sp, color: const Color(0xFF999999)),
              ),
            ],
          ),
          SizedBox(height: 8.h),
          ClipRRect(
            borderRadius: BorderRadius.circular(4.r),
            child: LinearProgressIndicator(
              value: total == 0 ? 0 : answered / total,
              minHeight: 6,
              backgroundColor: const Color(0xFFF0F2F5),
              valueColor: const AlwaysStoppedAnimation(Color(0xFF3B82F6)),
            ),
          ),
        ],
      ),
    );
  }

  /// 底部导航：上一题 / 答题卡 / 下一题
  Widget _buildBottomBar(List<ExamQuestion> questions) {
    final isFirst = _currentIndex == 0;
    final isLast = _currentIndex == questions.length - 1;
    return Container(
      padding: EdgeInsets.symmetric(horizontal: 16.w, vertical: 10.h),
      decoration: const BoxDecoration(
        color: Colors.white,
        border: Border(top: BorderSide(color: Color(0xFFF0F2F5))),
      ),
      child: Row(
        children: [
          Expanded(
            child: OutlinedButton.icon(
              onPressed: isFirst
                  ? null
                  : () => _pageController.previousPage(
                        duration: const Duration(milliseconds: 250),
                        curve: Curves.easeOut,
                      ),
              icon: const Icon(Icons.chevron_left, size: 18),
              label: const Text('上一题'),
            ),
          ),
          SizedBox(width: 12.w),
          Expanded(
            child: FilledButton.tonalIcon(
              onPressed: () => _openAnswerSheet(questions),
              icon: const Icon(Icons.grid_view, size: 18),
              label: const Text('答题卡'),
            ),
          ),
          SizedBox(width: 12.w),
          Expanded(
            child: FilledButton.icon(
              onPressed: isLast
                  ? null
                  : () => _pageController.nextPage(
                        duration: const Duration(milliseconds: 250),
                        curve: Curves.easeOut,
                      ),
              icon: const Icon(Icons.chevron_right, size: 18),
              label: const Text('下一题'),
            ),
          ),
        ],
      ),
    );
  }
}