迭代器&生成器

async function* streamToAsyncGen<T>(
  stream: ReadableStream<T>
): AsyncGenerator<T> {
  const reader = stream.getReader();
  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) return;
      yield value;  // ← 每个 chunk 惰性 yield
    }
  } finally {
    reader.releaseLock();  // ← 确保释放锁
  }
}

// 使用场景：逐行读取 1GB CSV
async function processHugeCSV(url: string) {
  const res = await fetch(url);
  const stream = res.body!;  // ReadableStream<Uint8Array>
  const decoder = new TextDecoder();
  let lineCount = 0;

  for await (const chunk of streamToAsyncGen(stream)) {
    const text = decoder.decode(chunk, { stream: true });
    const lines = text.split("\n");
    for (const line of lines) {
      lineCount++;
      if (lineCount > 10000) return; // ← 随时停止
      await processLine(line);
    }
  }
}

// 异步生成器配合 RSC 实现流式页面
async function* generatePageData(query: string) {
  // 第一批：立即返回缓存数据
  yield { type: "cache", data: await getCached(query) };

  // 第二批：数据库查询结果
  const dbResults = await db.search(query);
  yield { type: "db", data: dbResults };

  // 第三批：AI 增强结果（最慢）
  const aiEnhanced = await ai.enhance(dbResults);
  yield { type: "ai", data: aiEnhanced };
}

// 在 Server Component 中使用
export default async function SearchPage({
  searchParams,
}: {
  searchParams: { q: string };
}) {
  const batches = [];
  for await (const batch of generatePageData(searchParams.q)) {
    batches.push(batch);
  }
  return <SearchResults batches={batches} />;
}