'use client';
import { useEffect, useState, type MouseEvent, type ReactNode } from 'react';
import {
  Terminal,
  ArrowUpRight,
  ArrowRight,
  ArrowLeft,
  Code2,
  Database,
  Layers3,
  ListTodo,
  MemoryStick,
  Container,
  Server,
  Activity,
  BookOpen,
  Download,
  Monitor,
  X,
  Check,
  Copy,
  Clock3,
  Video as VideoIcon,
  ChevronRight,
  FileCode2,
  ExternalLink,
} from 'lucide-react';
import {
  Sidebar,
  SidebarProvider,
  SidebarContent,
  SidebarHeader,
  SidebarFooter,
  SidebarTrigger,
  useSidebar,
} from '@/components/ui/sidebar';
import { Button } from '@/components/ui/button';
import {
  Table,
  TableHeader,
  TableBody,
  TableRow,
  TableHead,
  TableCell,
} from '@/components/ui/table';
import { ProtocolDemo, HttpDemo, AsyncDemo } from './demos';
import type { Lesson, Video } from './lesson-types';
import lessonData from './lessons.json';
import videoData from './videos.json';

const lessons = lessonData as Lesson[];
const videos = videoData as Record<string, Video>;
const modules = [
  { name: 'API 服务开发', slug: 'api', icon: Code2 },
  { name: '数据库开发', slug: 'database', icon: Database },
  { name: 'API + 数据库', slug: 'api-database', icon: Layers3 },
  { name: '异步任务开发', slug: 'tasks', icon: ListTodo },
  { name: 'Redis 缓存', slug: 'redis', icon: MemoryStick },
  { name: 'Docker 容器化', slug: 'docker', icon: Container },
  { name: 'Linux 部署', slug: 'linux', icon: Server },
  { name: '线上问题排查', slug: 'troubleshooting', icon: Activity },
];
const phases = [
  {
    name: '起步与 HTTP',
    range: '01—04',
    description: '让服务运行，读懂请求，约束输入与输出。',
    from: 0,
    to: 4,
  },
  {
    name: 'REST 接口',
    range: '05—08',
    description: '围绕资源编写增删改查，处理错误与公共依赖。',
    from: 4,
    to: 8,
  },
  {
    name: '异步与调用',
    range: '09—10',
    description: '理解 I/O 等待，完成服务调用与浏览器联调。',
    from: 8,
    to: 10,
  },
  {
    name: '流式与实时通信',
    range: '11—16',
    description: '逐段读取响应，建立双向连接，完成接口验收。',
    from: 10,
    to: 16,
  },
];
const lessonSections = [
  ['objectives', '本节目标'],
  ['video', '课程视频'],
  ['concepts', '必要概念'],
  ['steps', '动手实现'],
  ['checks', '验收结果'],
  ['pitfalls', '常见错误'],
  ['exercise', '课后练习'],
  ['references', '技术文档'],
];
const overviewSections = [
  ['path', '学习路径'],
  ['communication', '通信方式演示'],
  ['project', '贯穿项目'],
  ['ready', '完成标准'],
];
type Navigate = (module: string, lesson?: string) => void;
function routeLink(module: string, lesson?: string) {
  return lesson
    ? `?lesson=${lesson}`
    : module === 'api'
      ? '?module=api'
      : `?module=${module}`;
}
function LocalLink({
  module = 'api',
  lesson,
  navigate,
  children,
  className,
  ...props
}: {
  module?: string;
  lesson?: string;
  navigate: Navigate;
  children: ReactNode;
  className?: string;
  'aria-current'?: 'page';
}) {
  return (
    <a
      href={routeLink(module, lesson)}
      className={className}
      {...props}
      onClick={(e: MouseEvent<HTMLAnchorElement>) => {
        if (e.button !== 0 || e.metaKey || e.ctrlKey || e.shiftKey || e.altKey)
          return;
        e.preventDefault();
        navigate(module, lesson);
      }}
    >
      {children}
    </a>
  );
}
function Navigation({
  active,
  lesson,
  navigate,
}: {
  active: string;
  lesson?: string;
  navigate: Navigate;
}) {
  const { setOpenMobile } = useSidebar();
  const go: Navigate = (m, l) => {
    navigate(m, l);
    setOpenMobile(false);
  };
  return (
    <Sidebar>
      <SidebarHeader>
        <LocalLink navigate={go} className="brand">
          <span className="brand-symbol">
            <Terminal size={21} />
          </span>
          <span>
            Agent 开发<span className="brand-sub">后端基础 · 补修课</span>
          </span>
        </LocalLink>
      </SidebarHeader>
      <SidebarContent>
        <div className="nav-caption">
          课程目录 <span>08 MODULES</span>
        </div>
        <nav className="module-nav" aria-label="课程模块">
          {modules.map((m) => (
            <LocalLink
              key={m.slug}
              module={m.slug}
              navigate={go}
              className={`module-link ${active === m.slug ? 'selected' : ''}`}
              aria-current={active === m.slug && !lesson ? 'page' : undefined}
            >
              <m.icon size={18} />
              <span>{m.name}</span>
              {m.slug === 'api' ? (
                <span className="nav-dot" />
              ) : (
                <span className="soon">待编写</span>
              )}
            </LocalLink>
          ))}
        </nav>
        {active === 'api' && lesson && (
          <nav className="lesson-nav" aria-label="API 课时">
            <div className="nav-caption">
              本模块课时 <span>16 LESSONS</span>
            </div>
            {phases.map((p) => (
              <div key={p.name}>
                <p className="lesson-nav-group">{p.name}</p>
                {lessons.slice(p.from, p.to).map((l) => (
                  <LocalLink
                    key={l.id}
                    lesson={l.id}
                    navigate={go}
                    className={`lesson-nav-link ${lesson === l.id ? 'current' : ''}`}
                    aria-current={lesson === l.id ? 'page' : undefined}
                  >
                    <span>{l.id}</span>
                    {l.title}
                  </LocalLink>
                ))}
              </div>
            ))}
          </nav>
        )}
      </SidebarContent>
      <SidebarFooter>
        <div className="sidebar-note">
          <BookOpen size={17} />
          <div>
            从 Python 到后端服务<small>先运行，再理解，再修改。</small>
          </div>
        </div>
      </SidebarFooter>
    </Sidebar>
  );
}

export default function Course() {
  const [module, setModule] = useState('api');
  const [lessonId, setLessonId] = useState<string>();
  const [presentation, setPresentation] = useState(false);
  const [notFound, setNotFound] = useState(false);
  const lesson = lessons.find((l) => l.id === lessonId);
  const current = modules.find((m) => m.slug === module)!;
  useEffect(() => {
    const read = () => {
      const q = new URLSearchParams(location.search);
      const id = q.get('lesson');
      const mod = q.get('module') || 'api';
      const validLesson = id ? lessons.some((l) => l.id === id) : true;
      const validModule = modules.some((m) => m.slug === mod);
      setNotFound(!validLesson || !validModule);
      setLessonId(validLesson && id ? id : undefined);
      setModule(validModule ? mod : 'api');
      if (id && validLesson) setModule('api');
    };
    read();
    window.addEventListener('popstate', read);
    return () => window.removeEventListener('popstate', read);
  }, []);
  useEffect(() => {
    document.title = `${lesson?.title || current.name} · Agent 开发补修课`;
  }, [lesson, current.name]);
  const navigate: Navigate = (mod, id) => {
    setModule(mod);
    setLessonId(id);
    setNotFound(false);
    history.pushState({}, '', routeLink(mod, id));
    window.scrollTo({ top: 0, behavior: 'instant' });
    requestAnimationFrame(() =>
      document.querySelector<HTMLElement>('h1')?.focus({ preventScroll: true }),
    );
  };
  return (
    <SidebarProvider
      className={presentation ? 'presentation' : ''}
      style={{ '--sidebar-width': '258px' } as React.CSSProperties}
    >
      <a className="skip-link" href="#main-content">
        跳到课件正文
      </a>
      <Navigation active={module} lesson={lessonId} navigate={navigate} />
      <div className="workspace">
        <header className="topbar">
          <div className="breadcrumbs">
            <SidebarTrigger aria-label="展开或收起课程目录" />
            <LocalLink navigate={navigate}>后端基础</LocalLink>
            <span>/</span>
            <strong>{current.name}</strong>
            {lesson && (
              <>
                <span>/</span>
                <span className="crumb-lesson">{lesson.id}</span>
              </>
            )}
          </div>
          <div className="topbar-actions">
            <a
              className="quiet-link docs-link"
              href="https://fastapi.tiangolo.com/"
              target="_blank"
              rel="noreferrer"
            >
              FastAPI 文档 <ArrowUpRight size={15} />
            </a>
            <Button
              variant="ghost"
              onClick={() => setPresentation((v) => !v)}
              aria-pressed={presentation}
            >
              {presentation ? <X /> : <Monitor />}
              <span>{presentation ? '退出授课' : '授课视图'}</span>
            </Button>
          </div>
        </header>
        <div className="document-grid">
          <main id="main-content">
            {notFound ? (
              <div className="pending-module">
                <h1 tabIndex={-1}>未找到该课件</h1>
                <p>该地址中的模块或课时不存在，请从课程目录重新选择。</p>
                <LocalLink navigate={navigate} className="primary-link">
                  返回 API 服务开发 <ArrowRight size={16} />
                </LocalLink>
              </div>
            ) : module !== 'api' ? (
              <PendingModule
                name={current.name}
                index={modules.findIndex((m) => m.slug === module) + 1}
                navigate={navigate}
              />
            ) : lesson ? (
              <LessonPage lesson={lesson} navigate={navigate} />
            ) : (
              <Overview navigate={navigate} />
            )}
          </main>
          <aside className="toc" aria-label="本页导航">
            <p>{lesson ? '本节导航' : '本模块导航'}</p>
            {(module === 'api'
              ? lesson
                ? lessonSections
                : overviewSections
              : [['reserved', '内容状态']]
            ).map(([id, label]) => (
              <a href={`#${id}`} key={id}>
                {label}
              </a>
            ))}
            <div className="toc-note">
              <span className="tiny-label">
                {lesson ? '本节实战' : '学习准备'}
              </span>
              <p>
                {lesson ? (
                  <>
                    {lesson.minutes} 分钟建议录制时长
                    <br />
                    完成代码后检查验收结果
                    <br />
                    遇到错误先看响应与日志
                  </>
                ) : (
                  <>
                    会写 Python 函数
                    <br />
                    了解列表与字典
                    <br />
                    能在终端执行命令
                  </>
                )}
              </p>
            </div>
            {module === 'api' && (
              <a
                href="/downloads/api-lab.zip"
                download
                className="toc-download"
              >
                <Download size={14} />
                示例项目
              </a>
            )}
          </aside>
        </div>
        <footer className="page-footer">
          <span>Agent 开发 · 后端基础补修课</span>
          <span>API 模块 / 课件版本 01</span>
        </footer>
      </div>
    </SidebarProvider>
  );
}
function Overview({ navigate }: { navigate: Navigate }) {
  const minutes = lessons.reduce((a, l) => a + l.minutes, 0);
  return (
    <>
      <div className="eyebrow">
        MODULE 01 <span /> 服务与通信
      </div>
      <h1 tabIndex={-1}>
        API 服务开发<span className="title-dot">.</span>
      </h1>
      <p className="lead">
        把 Python 函数变成可以被调用的服务。
        <br />
        从第一个请求开始，完成 REST 接口、流式输出与双向通信。
      </p>
      <div className="meta-row">
        <span>Python 3.11+</span>
        <span>FastAPI / Pydantic 2</span>
        <span>{lessons.length} 节实战课</span>
        <span>
          建议录制约 {Math.floor(minutes / 60)} 小时 {minutes % 60} 分
        </span>
      </div>
      <div className="overview-actions">
        <LocalLink lesson="01" navigate={navigate} className="primary-link">
          开始第一节 <ArrowRight size={16} />
        </LocalLink>
        <a href="/downloads/api-lab.zip" download className="secondary-link">
          <Download size={16} />
          下载示例项目
        </a>
        <span className="material-state">课件可读 · 视频待录制</span>
      </div>
      <div className="module-intro">
        <span className="section-index">BUILD 01</span>
        <div>
          <h3>贯穿项目：笔记与消息服务</h3>
          <p>
            创建与查询笔记，校验请求，逐段输出消息，建立实时连接。数据暂存在内存中，重启后清空。
          </p>
        </div>
      </div>
      <section id="path">
        <div className="section-heading">
          <h2>学习路径</h2>
          <span>每节：概念 → 实战 → 验收</span>
        </div>
        <div className="curriculum">
          {phases.map((p, i) => (
            <div className="phase" key={p.name}>
              <div className="phase-heading">
                <span className="phase-marker">
                  {String(i + 1).padStart(2, '0')}
                </span>
                <div>
                  <h3>{p.name}</h3>
                  <p>{p.description}</p>
                </div>
                <span className="phase-range">{p.range}</span>
              </div>
              <div className="lesson-rows">
                {lessons.slice(p.from, p.to).map((l) => (
                  <LocalLink
                    key={l.id}
                    lesson={l.id}
                    navigate={navigate}
                    className="lesson-row"
                  >
                    <span className="lesson-number">{l.id}</span>
                    <div>
                      <strong>{l.title}</strong>
                      <p>{l.summary}</p>
                    </div>
                    {l.demo && <span className="interactive-badge">交互</span>}
                    <span className="lesson-duration">{l.minutes} 分</span>
                    <ChevronRight size={15} />
                  </LocalLink>
                ))}
              </div>
            </div>
          ))}
        </div>
      </section>
      <section id="communication">
        <div className="section-heading">
          <h2>HTTP、SSE 与 WebSocket 通信过程</h2>
          <LocalLink lesson="11" navigate={navigate} className="quiet-link">
            进入第 11 节 <ArrowUpRight size={14} />
          </LocalLink>
        </div>
        <ProtocolDemo />
        <p className="section-caption">
          REST 描述接口设计约定；SSE 和 WebSocket
          描述不同的通信方式。流式响应本身仍然可以基于 HTTP。
        </p>
      </section>
      <section id="project">
        <div className="section-heading">
          <h2>示例项目接口</h2>
          <span>api-lab / 本地运行</span>
        </div>
        <p>
          一个可以通过浏览器、命令行和测试代码调用的 FastAPI
          服务。消息由固定逻辑生成，运行示例不需要模型 API Key。
        </p>
        <Table className="api-table">
          <TableHeader>
            <TableRow>
              <TableHead>入口</TableHead>
              <TableHead>可观察的结果</TableHead>
              <TableHead>对应课时</TableHead>
            </TableRow>
          </TableHeader>
          <TableBody>
            {[
              ['GET /health', '返回服务状态', '01'],
              ['GET / POST /notes', '查询与创建笔记', '05—06'],
              [
                'GET / PUT / DELETE /notes/{id}',
                '读取、完整替换与删除',
                '06—07',
              ],
              ['GET /private', '校验 X-API-Key 请求头', '08'],
                ['GET /slow', '并发等待 I/O', '09'],
                ['GET /upstream-demo', '调用上游接口并处理超时', '10'],
              ['POST /generate', '一次返回完整 JSON', '11'],
              ['GET /stream', '连续收到 token，最后收到 done', '12—13'],
              ['WS /ws', '收发 echo 与 ping / pong 消息', '14—15'],
            ].map(([path, result, id]) => (
              <TableRow key={path}>
                <TableCell>
                  <code>{path}</code>
                </TableCell>
                <TableCell>{result}</TableCell>
                <TableCell className="mono">{id}</TableCell>
              </TableRow>
            ))}
          </TableBody>
        </Table>
        <div className="resource-strip">
          <FileCode2 size={25} />
          <div>
            <h3>配套代码与浏览器客户端</h3>
            <p>包含 README、版本依赖、接口测试与 web-client.html。</p>
          </div>
          <a href="/downloads/api-lab.zip" download className="secondary-link">
            下载 ZIP <Download size={15} />
          </a>
        </div>
      </section>
      <section id="ready">
        <div className="section-heading">
          <h2>模块完成标准</h2>
          <span>用实际结果判断是否掌握</span>
        </div>
        <ul className="check-list">
          {[
            '能从空目录启动服务，并用 /docs 或 curl 发出请求。',
            '能完成笔记的创建、查询、修改与删除，区分 201、204、401、404、422。',
            '能解释 await 等待期间另一个请求为什么可以被处理。',
            '能逐段显示 SSE 数据，在完成或取消时释放连接。',
            '能建立 WebSocket 连接，收发消息并处理断开。',
            '能运行测试，独立定位参数、方法、跨域与连接问题。',
          ].map((s) => (
            <li key={s}>
              <Check size={16} />
              {s}
            </li>
          ))}
        </ul>
        <div className="next-module">
          <span>后续模块</span>
          <strong>数据库开发</strong>
          <span className="soon">待本模块完善后编写</span>
        </div>
      </section>
    </>
  );
}

function PendingModule({
  name,
  index,
  navigate,
}: {
  name: string;
  index: number;
  navigate: Navigate;
}) {
  return (
    <div className="pending-module" id="reserved">
      <div className="eyebrow">
        MODULE {String(index).padStart(2, '0')} <span /> 课程目录
      </div>
      <h1 tabIndex={-1}>
        {name}
        <span className="title-dot">.</span>
      </h1>
      <span className="status-label">待编写</span>
      <p className="lead">
        该模块已保留课程入口。
        <br />
        API 服务开发模块完善后，再补充本模块的课件、实战与视频。
      </p>
      <LocalLink navigate={navigate} className="primary-link">
        返回 API 服务开发 <ArrowRight size={16} />
      </LocalLink>
    </div>
  );
}

function CodeBlock({
  code,
  lang = 'text',
  filename,
}: {
  code: string;
  lang?: string;
  filename?: string;
}) {
  const [copied, setCopied] = useState(false);
  const [error, setError] = useState(false);
  useEffect(() => {
    if (!copied && !error) return;
    const t = setTimeout(() => {
      setCopied(false);
      setError(false);
    }, 2200);
    return () => clearTimeout(t);
  }, [copied, error]);
  const copy = async () => {
    try {
      await navigator.clipboard.writeText(code);
      setCopied(true);
    } catch {
      setError(true);
    }
  };
  const highlight = (line: string) =>
    line
      .split(
        /("(?:[^"\\]|\\.)*"|'(?:[^'\\]|\\.)*'|#[^\n]*|\b(?:from|import|async|await|def|return|class|if|else|elif|for|in|while|try|except|finally|raise|with|as|yield|True|False|None|const|let|new|function|throw)\b)/g,
      )
      .map((part, i) => (
        <span
          key={i}
          className={
            part.startsWith('#')
              ? 'syntax-comment'
              : /^['"]/.test(part)
                ? 'syntax-string'
                : /^(from|import|async|await|def|return|class|if|else|elif|for|in|while|try|except|finally|raise|with|as|yield|True|False|None|const|let|new|function|throw)$/.test(
                      part,
                    )
                  ? 'syntax-keyword'
                  : undefined
          }
        >
          {part}
        </span>
      ));
  return (
    <div className="code-block">
      <div className="code-toolbar">
        <span>
          <FileCode2 size={14} />
          {filename || lang}
        </span>
        <button onClick={copy} className="copy-button" aria-label="复制代码">
          {copied ? <Check size={13} /> : <Copy size={13} />}
          <span aria-live="polite">
            {copied ? '已复制' : error ? '请选择代码手动复制' : '复制'}
          </span>
        </button>
      </div>
      <pre>
        <code>
          {code.split('\n').map((line, i) => (
            <span className="code-line" key={i}>
              <span className="line-number" aria-hidden="true">
                {i + 1}
              </span>
              <span>{highlight(line) || ' '}</span>
              {'\n'}
            </span>
          ))}
        </code>
      </pre>
    </div>
  );
}
function VideoBlock({ id }: { id: string }) {
  const video = videos[id];
  const valid = video && /^(https?:\/\/|\/(?!\/))/.test(video.url);
  return (
    <section id="video" className="video-section">
      {valid ? (
        video.type === 'file' ? (
          <div className="video-player">
            <video controls preload="metadata" src={video.url} playsInline>
              <a href={video.url}>在浏览器打开课程视频</a>
            </video>
            <a href={video.url} target="_blank" rel="noreferrer">
              无法播放时，直接打开视频 <ExternalLink size={14} />
            </a>
          </div>
        ) : (
          <a
            href={video.url}
            target="_blank"
            rel="noreferrer"
            className="video-pending"
          >
            <VideoIcon size={23} />
            <div>
              <strong>{video.title || '观看本节课程视频'}</strong>
              <span>在课程视频平台打开</span>
            </div>
            <ArrowUpRight size={20} />
          </a>
        )
      ) : (
        <div className="video-pending">
          <VideoIcon size={23} />
          <div>
            <strong>本节视频待录制</strong>
            <span>可先按下方课件完成实战步骤。</span>
          </div>
          <span className="status-label">课件已就绪</span>
        </div>
      )}
    </section>
  );
}
function LessonPage({
  lesson: l,
  navigate,
}: {
  lesson: Lesson;
  navigate: Navigate;
}) {
  const index = lessons.findIndex((x) => x.id === l.id);
  return (
    <article key={l.id} className="lesson-article">
      <LocalLink navigate={navigate} className="back-link">
        <ArrowLeft size={14} />
        API 服务开发 · 全部课时
      </LocalLink>
      <div className="eyebrow">
        LESSON {l.id} / 16 <span />
        {l.group}
      </div>
      <h1 className="lesson-title" tabIndex={-1}>
        {l.title}
      </h1>
      <p className="lead">{l.summary}</p>
      <div className="meta-row">
        <span>
          <Clock3 size={13} />
          {l.minutes} 分钟建议录制
        </span>
        <span>实战课件</span>
        <span>{l.demo ? '含交互演示' : '含代码与练习'}</span>
      </div>
      <section id="objectives" className="objectives">
        <h2>本节目标</h2>
        <ul>
          {l.objectives.map((o, i) => (
            <li key={o}>
              <span>{String(i + 1).padStart(2, '0')}</span>
              {o}
            </li>
          ))}
        </ul>
      </section>
      <VideoBlock id={l.id} />
      <section id="concepts">
        <div className="section-heading">
          <h2>必要概念</h2>
          <span>先明确代码在做什么</span>
        </div>
        {l.concepts.map((c, i) => (
          <div className="concept" key={c.title}>
            <h3>
              <span>{i + 1}.</span>
              {c.title}
            </h3>
            <p>{c.body}</p>
          </div>
        ))}
        {l.demo === 'http' ? (
          <HttpDemo />
        ) : l.demo === 'async' ? (
          <AsyncDemo />
        ) : l.demo === 'protocol' ? (
          <ProtocolDemo />
        ) : null}
      </section>
      <section id="steps">
        <div className="section-heading">
          <h2>动手实现</h2>
          <span>{l.steps.length} 个步骤</span>
        </div>
        {l.steps.map((s, i) => (
          <div className="practice-step" key={s.title}>
            <div className="practice-title">
              <span>{String(i + 1).padStart(2, '0')}</span>
              <h3>{s.title}</h3>
            </div>
            <p>{s.body}</p>
            {s.code && (
              <CodeBlock code={s.code} lang={s.lang} filename={s.filename} />
            )}
          </div>
        ))}
      </section>
      <section id="checks">
        <div className="section-heading">
          <h2>验收结果</h2>
          <span>检查响应与运行行为</span>
        </div>
        <ul className="check-list">
          {l.checks.map((c) => (
            <li key={c}>
              <Check size={16} />
              {c}
            </li>
          ))}
        </ul>
      </section>
      <section id="pitfalls">
        <div className="section-heading">
          <h2>常见错误</h2>
          <span>现象 → 原因 → 处理</span>
        </div>
        <div className="pitfall-list">
          {l.pitfalls.map((p) => (
            <div className="pitfall" key={p.symptom}>
              <h3>{p.symptom}</h3>
              <p>
                <strong>原因</strong>
                {p.cause}
              </p>
              <p>
                <strong>处理</strong>
                {p.fix}
              </p>
            </div>
          ))}
        </div>
      </section>
      <section id="exercise" className="exercise">
        <div className="section-heading">
          <h2>扩展练习</h2>
          <span>课后练习</span>
        </div>
        <p>{l.exercise.task}</p>
        <details>
          <summary>
            查看提示 <ChevronRight size={15} />
          </summary>
          <p>{l.exercise.hint}</p>
        </details>
        <details>
          <summary>
            查看参考答案 <ChevronRight size={15} />
          </summary>
          <div className="answer-text">{l.exercise.answer}</div>
        </details>
      </section>
      <section id="references">
        <div className="section-heading">
          <h2>技术文档</h2>
          <span>对照原始定义与框架用法</span>
        </div>
        <div className="reference-links">
          {l.refs.map((r) => (
            <a key={r.url} href={r.url} target="_blank" rel="noreferrer">
              {r.label}
              <ArrowUpRight size={15} />
            </a>
          ))}
        </div>
      </section>
      <div className="lesson-pagination">
        {index > 0 ? (
          <LocalLink navigate={navigate} lesson={lessons[index - 1].id}>
            <span>
              <ArrowLeft size={13} />
              上一节
            </span>
            <strong>{lessons[index - 1].title}</strong>
          </LocalLink>
        ) : (
          <LocalLink navigate={navigate}>
            <span>
              <ArrowLeft size={13} />
              模块概览
            </span>
            <strong>查看完整学习路径</strong>
          </LocalLink>
        )}
        {index < lessons.length - 1 ? (
          <LocalLink
            navigate={navigate}
            lesson={lessons[index + 1].id}
            className="next"
          >
            <span>
              下一节
              <ArrowRight size={13} />
            </span>
            <strong>{lessons[index + 1].title}</strong>
          </LocalLink>
        ) : (
          <LocalLink navigate={navigate} className="next">
            <span>
              本模块课件结束
              <Check size={13} />
            </span>
            <strong>返回模块完成标准</strong>
          </LocalLink>
        )}
      </div>
    </article>
  );
}