class EventEmitter {
  _infinty = 2;
  constructor(maxListeners) {
    this.events = {};
    this.maxListeners = maxListeners || this._infinty;
  }

  emit(event, ...args) {
    const cbs = this.events[event];
    if (!cbs) {
      console.log("没有这个事件");
      return this;
    }

    cbs.forEach((cb) => cb.apply(this, args));
    return this;
  }

  on(event, cb) {
    if (!this.events[event]) {
      this.events[event] = [];
    }
    //TODO 拦截最大监听
    if(this.maxListeners !== this._infinty && this.events[event].length >= this.maxListeners){
        console.warn(`当前事件${event}超过最大监听数`)
        return this
    }
    this.events[event].push(cb);
    return this;
  }

  once(event, cb) {
    const func = (...args) => {
      this.off(event, func);
      cb.apply(this.args);
    };
    
    this.on(event, func);
    return this;
  }

  off(event, cb) {
    if (!cb) {
      this.events[event] = null;
    } else {
      this.events[event] = this.events[event].filter((item) => item !== cb);
    }
    return this;
  }
}

const add = (a, b) => console.log(a + b);
const log = (...args) => console.log(...args);

const even = new EventEmitter();

even.on("add", add);
even.on("log", log);
even.emit("add", 1, 2);
even.emit("log", "he huy");
even.off("add");
even.once("once", add);