const name = '@@EventEmitter'
const id_Identifier = '__id__'

/**
 * generate random id
 */
function randomId() {
  return Math.random().toString(36).substr(2, 16)
}

/**
 * find id
 * @param id
 */
function findIndexById(this: CallbackFunc[], id: string) {
  return this.findIndex((callback) => callback[id_Identifier] === id)
}

type CallbackFunc = { [id_Identifier]?: string } & ((...dataArray: any[]) => void)

export default class EventEmitter {
  [name]: Record<string, CallbackFunc[]>
  static Events = {
    global: '*',
  }

  constructor() {
    this[name] = {}
  }

  on(event: string, listener: CallbackFunc) {
    let events = this[name]
    let container = (events[event] = events[event] || [])
    let id = randomId()
    let index = -1
    listener[id_Identifier] = id
    container.push(listener)
    return () => {
      index = findIndexById.call(container, id)
      index >= 0 && container.splice(index, 1)
    }
  }

  off(event: string) {
    this[name][event] = []
  }

  clear() {
    this[name] = {}
  }

  once(event: string, listener: CallbackFunc) {
    let self = this
    let events = self[name]
    let container = (events[event] = events[event] || [])
    let id = randomId()
    let index = -1
    let callback: CallbackFunc = function (...dataArray: any[]) {
      index = findIndexById.call(container, id)
      index >= 0 && container.splice(index, 1)
      listener.apply(self, dataArray)
    }

    callback[id_Identifier] = id
    container.push(callback)
  }

  emit(event: string, ...dataArray: any[]) {
    let self = this
    let events = self[name]
    let triggers = (events[EventEmitter.Events.global] || []).concat(events[event] || [])
    triggers.length > 0 && triggers.map((listener) => listener.apply(self, dataArray))
  }
}