export default class Emitter {
  on(name, fn, ctx) {
    const e = this.e || (this.e = {});
    (e[name] || (e[name] = [])).push({ fn, ctx })
    return this
  }

  once(name, fn, ctx) {
    const self = this
    function listener(...args) {
      self.off(name, listener)
      fn.apply(ctx, args)
    }
    listener._ = fn
    return this.on(name, listener, ctx)
  }

  emit(name, ...data) {
    const evtArr = ((this.e || (this.e = {}))[name] || []).slice()
    for (let i = 0; i < evtArr.length; i += 1) {
      evtArr[i].fn.apply(evtArr[i].ctx, data)
    }
    return this
  }

  off(name, callback) {
    const e = this.e || (this.e = {})
    const evts = e[name]
    const liveEvents = []
    if (evts && callback) {
      for (let i = 0, len = evts.length; i < len; i += 1) {
        if (evts[i].fn !== callback && evts[i].fn._ !== callback)
          liveEvents.push(evts[i])
      }
    }
    if (liveEvents.length) {
      e[name] = liveEvents
    }
    else {
      delete e[name]
    }
    return this
  }
}