/** Serialize local saves so each request reads the revision returned by the last. */
export function createCanvasSaveQueue() {
  let pending: Promise<unknown> = Promise.resolve();
  const queue = {
    enqueue<T>(save: () => Promise<T>): Promise<T> {
      const next = pending.then(save, save);
      pending = next.catch(() => undefined);
      return next;
    },
    enqueueOperation(save: () => Promise<boolean>, operation: () => Promise<void>) {
      return queue.enqueue(async () => {
        if (!(await save())) {
          throw new Error("画布尚未保存成功，请确认网络或画布同步状态后重试");
        }
        await operation();
      });
    },
  };
  return queue;
}