// 史前时代的回调深渊
getData(function(a) {
  getMoreData(a, function(b) {
    getEvenMoreData(b, function(c) {
      // 更多嵌套...
    });
  });
});

// 链式调用
getData()
  .then(a => getMoreData(a))
  .then(b => getEvenMoreData(b))
  .then(c => getFinalData(c))
  .then(result => console.log(result))
  .catch(err => console.error(err));

async function fetchUserData() {
  try {
    const response = await fetch('/api/user');
    return await response.json();
  } catch (error) {
    throw new Error(`数据获取失败: ${error.message}`);
  }
}

console.log('序幕开启');

async function performAsyncDance() {
  console.log('舞步开始');
  await Promise.resolve(); // 微任务分界点
  console.log('优雅转身');
}

performAsyncDance();
console.log('主旋律继续');

// 低效的串行等待
async function inefficientFetch() {
  const user = await fetchUser();    // 等待200ms
  const posts = await fetchPosts();  // 再等待200ms
  const comments = await fetchComments(); // 再等待200ms
  // 总耗时约600ms
}

// 高效的并行发起
async function efficientFetch() {
  const [user, posts, comments] = await Promise.all([
    fetchUser(),
    fetchPosts(),
    fetchComments()
  ]);
  // 总耗时约200ms
}

async function loadContentBasedOnRole() {
  const user = await authenticateUser();
  
  if (user.role === 'admin') {
    const [dashboard, analytics] = await Promise.all([
      fetchAdminDashboard(),
      fetchAnalytics()
    ]);
    return renderAdminView(dashboard, analytics);
  } else {
    const content = await fetchUserContent(user.id);
    return renderUserView(content);
  }
}

// 危险的裸露await
async function riskyOperation() {
  const data = await fetchUnreliableAPI(); // 可能崩溃的悬崖
  return processData(data);
}

// 安全的错误处理
async function safeOperation() {
  try {
    const data = await fetchUnreliableAPI();
    return processData(data);
  } catch (error) {
    logger.error('操作失败', error);
    return getFallbackData();
  }
}

// 错误的forEach用法
urls.forEach(async url => {
  const response = await fetch(url); // 这里的await是孤岛
});

// 正确的循环处理
// 并行处理
await Promise.all(urls.map(async url => {
  const response = await fetch(url);
  return response.json();
}));

// 顺序处理
for (const url of urls) {
  const response = await fetch(url); // 确保顺序执行
  process(await response.json());
}

async function processLargeDataset(dataStream) {
  for await (const chunk of dataStream) {
    await processChunk(chunk); // 优雅处理数据流
  }
}

async function resilientFetch(url, maxRetries = 3) {
  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      const response = await fetch(url);
      return await response.json();
    } catch (error) {
      if (attempt === maxRetries) throw error;
      await delay(attempt * 1000); // 指数退避策略
    }
  }
}

async function fetchWithTimeout(url, timeoutMs = 5000) {
  const fetchPromise = fetch(url);
  const timeoutPromise = new Promise((_, reject) => {
    setTimeout(() => reject(new Error('请求超时')), timeoutMs);
  });
  
  return await Promise.race([fetchPromise, timeoutPromise]);
}