export default defineBackground(() => {
  console.log('Hello background!', { id: browser.runtime.id });

  // 监听下载请求
  browser.runtime.onMessage.addListener(async (msg) => {
    if (msg.type === 'DOWNLOAD_PINS') {
      const pins: PinData[] = msg.pins;
      const concurrency: number = msg.concurrency || 3;
      const result = await startBatchDownload(pins, concurrency);
      // 通知 popup 下载完成
      browser.runtime.sendMessage({
        type: 'DOWNLOAD_DONE',
        success: result.success,
        failed: result.failed,
        total: result.total,
      });
    }
  });
});

// 定义单个下载任务 (封装成 Promise)
async function downloadOne(pin: PinData): Promise<void> {
  return new Promise(async (resolve) => {
    // 处理文件名非法字符（清理文件名）
    const safeName = (pin.title || 'image').replace(/[\n\r\t]/g, ' ').replace(/[<>:"/\\|?*]/g, '').replace(/\s+/g, ' ').trim().slice(0, 100);
    const filename = `Pins/${safeName}.jpg`;

    browser.downloads.download({
      url: pin.imgSrc,
      filename: filename,
      headers: [{ name: 'Referer', value: 'https://huaban.com/' }],
      conflictAction: 'uniquify'
    }, (id) => {
      if (!id) {
        console.warn(`跳过: ${pin.title} (可能 URL 无效)`);
        return resolve(); // 即使失败也要 resolve，否则会阻塞队列
      }

      // 监听下载状态，只有当下载真正完成（或中断）时才释放资源
      const listener = (delta: Browser.downloads.DownloadDelta) => {
        if (delta.id !== id) return;

        if (delta.state && delta.state.current === 'complete') {
          browser.downloads.onChanged.removeListener(listener);
          resolve();
        }
        // 处理中断或取消的情况，防止队列卡死
        else if (delta.state && delta.state.current === 'interrupted') {
          browser.downloads.onChanged.removeListener(listener);
          console.warn(`下载中断: ${pin.title}`, JSON.stringify(delta));
          resolve();
        }
      };
      browser.downloads.onChanged.addListener(listener);
    });
  });
}

// 并发调度器
export async function startBatchDownload(pins: PinData[], limit: number = 3) {
  let success = 0;
  let failed = 0;

  const executing: Promise<void>[] = []; // 正在运行的任务池

  for (const pin of pins) {
    // 创建任务
    const task = downloadOne(pin);

    // 加入任务池
    const wrapper = task.finally(() => {
      const idx = executing.indexOf(wrapper);
      if (idx !== -1) executing.splice(idx, 1);
    });
    executing.push(wrapper);

    // 关键逻辑：如果池子满了（达到 limit），等待任意一个任务完成
    if (executing.length >= limit) {
      await Promise.race(executing);
    }
  }

  // 等待剩余任务全部完成
  await Promise.all(executing);
  console.log("所有下载任务已处理完毕");

  return { success, failed, total: pins.length };
}