class EventEmitter {

  protected callbacks: Map<string, Set<(evt: any) => void>>

  constructor() {
    this.callbacks = new Map()
  }

  /** Emits an event on this event emitter */
  emit (name: string, evt: any): this {
    const callbacks = this.callbacks.get(name)
    if (callbacks) {
      callbacks.forEach(cb => {
        cb(evt)
      })
    }
    return this
  }

  /** Adds an event listener */
  on (name: string, cb: (evt: any) => void): this {
    const set = this.callbacks.get(name) || new Set()
    this.callbacks.set(name, set)
    set.add(cb)
    return this
  }

  /** Removes an event listener */
  off (name: string, cb?: (evt: any) => void): this {
    if (cb) {
      const set = this.callbacks.get(name)
      if (set) {
        set.delete(cb)
      }

      if (set.size === 0) {
        this.callbacks.delete(name)
      }
    } else {
      this.callbacks.delete(name)
    }
    return this
  }
}

export {
  EventEmitter
}