type fn = (...args: any[]) => void
export function emitter() {
  const events = new Map<string, fn[]>()

  function get(name: string) {
    if (events.has(name))
      return events.get(name)!
    return []
  }

  /**
   * 订阅事件
   */
  function on(name: string, cb: fn) {
    if (!events.has(name))
      events.set(name, [])

    get(name).push(cb)

    return () => {
      off(name, cb)
    }
  }

  /**
   * 发布事件
   */
  function emit(name: string, ...args: any[]) {
    get(name).forEach(cb => cb(...args))
  }

  /**
   * 取消订阅
   */
  function off(name: string, cb: fn) {
    const cbs = get(name)
    const index = cbs.indexOf(cb)
    if (index > -1)
      cbs.splice(index, 1)
  }

  /**
   * 只订阅一次
   */
  function once(name: string, cb: fn) {
    const off = on(name, (...args: any[]) => {
      off()
      cb(...args)
    })

    return off
  }

  /**
   * 发布全部事件
   */
  function emitAll(...args: any[]) {
    events.forEach((cbs, _name) => {
      cbs.forEach(cb => cb(...args))
    })
  }

  /**
   * 清空所有事件
   */
  function clear() {
    events.clear()
  }

  return {
    on,
    emit,
    off,
    once,
    emitAll,
    clear,
  }
}

export type Emitter = ReturnType<typeof emitter>