declare type Fn<T = any> = () => T
/**
 * 每个单例的 id
 *
 * The id of a singleton
 * */
declare type ID = string | number

export interface PromiseOnPendingOptions {
  id?: ID
  /**
   * 用于延迟 Promise 实例删除，
   * 如果为 undefined，则在 promise 状态改变之后立即删除
   *
   * Used to delay the deletion of Promise instance,
   * if it is undefined, the promise will be deleted immediately after the state changed
   *
   * This option will be deprecated in next version
   * */
  delayTime?: number
  /**
   * 同 delayTime
   * 推荐使用这个属性
   *
   * As same as delayTime
   * */
  cacheTime?: number
}

/**
 * @deprecated 这个方法使用多了会导致内存泄漏，建议使用 singleton 方法代替
 * @desc 返回 id 对应的一个单例对象
 *
 *       Return a singleton of an object(such as Promise, Function, Object...) corresponding to the id.
 * */
declare function singletonObj<T extends any>(id: ID, defaultValue?: () => T): T

/**
 * @desc 返回 id 对应的一个单例对象，这个方法应当配合返回的 delete 方法一起使用，否则使用多了会导致内存泄漏
 *
 *       Return a singleton of an object(such as Promise, Function, Object...) corresponding to the id.
 *       This method will cause OOM if it's used too much without calling `delete`.
 * */
declare function singleton<T extends any>(
  id: ID,
  defaultValue?: () => T,
): {
  value: T
  delete(): void
}

/**
 * @desc 保证一个 id 对应的 promise 在同一时间只存在一个，
 *       并且生成 promise 的函数在 promise pending 状态的时间段内只执行一次，
 *       这个方法可以用来减少同一时间的多余请求
 *
 *       Ensure that only one promise corresponding to the id exists at the same time,
 *       and the function that generates the promise executes only once
 *       during the period of promise pending.
 *       This method can be used to reduce redundant requests at the same time
 * */
declare function promiseOnPending<P extends PromiseLike<any>>(
  proFn: () => P,
  options: PromiseOnPendingOptions,
): P

/**
 * @desc 封装 setInterval 函数，
 *       保证同一个 id 对应的计时器只有一个在运行，
 *       并且返回一个清除计时器的函数，方便随时终止计时器
 *
 *       A wrapper of the setInterval function,
 *       make sure only one timer for the same id is running,
 *       and returns a function to clear the timer so it can be terminated at any time
 * */
declare function runInterval(id: ID, createFn: Fn): () => void

/**
 * @desc 保证传入的函数在程序的运行期间只运行一次
 *
 *       Ensure that the incoming function runs only once during the run time of the program
 * */
declare function onceRun(fn: Fn, id?: any): void

export { onceRun, promiseOnPending, runInterval, singleton, singletonObj }