export interface SerialTaskQueue {
  enqueue<T>(task: () => Promise<T>): Promise<T>;
  idle(): Promise<void>;
}

/**
 * Runs asynchronous tasks one at a time in enqueue order. A rejected task is
 * returned to its caller but does not poison the queue for later work.
 */
export function createSerialTaskQueue(): SerialTaskQueue {
  let tail: Promise<void> = Promise.resolve();

  return {
    enqueue<T>(task: () => Promise<T>): Promise<T> {
      const result = tail.then(task);
      tail = result.then(
        () => undefined,
        () => undefined,
      );
      return result;
    },
    idle(): Promise<void> {
      return tail;
    },
  };
}