/** 按输入顺序执行有界并发映射，避免一次创建过多异步任务。 */
export async function mapWithConcurrency<T, R>(
  items: readonly T[],
  concurrency: number,
  worker: (item: T, index: number) => Promise<R>,
): Promise<R[]> {
  if (items.length === 0) {
    return [];
  }

  const workerCount = Math.max(1, Math.min(items.length, Math.floor(concurrency) || 1));
  const results = Array.from<R>({ length: items.length });
  let nextIndex = 0;
  let failed = false;

  /** 领取并处理下一个尚未执行的输入项。 */
  async function runWorker(): Promise<void> {
    for (;;) {
      if (failed) {
        return;
      }
      const index = nextIndex;
      nextIndex += 1;
      if (index >= items.length) {
        return;
      }
      try {
        results[index] = await worker(items[index] as T, index);
      } catch (error) {
        failed = true;
        throw error;
      }
    }
  }

  await Promise.all(Array.from({ length: workerCount }, () => runWorker()));
  return results;
}