import { describe, expect, test, jest } from "@jest/globals";

type IListeners = {
  name: string,
  callback: (...args:any[]) => void
}

class EventEmitter {
  protected Listeners:IListeners[] = [];
  public addEventListener(eventName: string, callback: (...args:any[]) => void) {
    this.Listeners.push({
      callback,
      name: eventName
    });
  }
  public trigger(eventName: string, data?: any) {
    this.Listeners.forEach(event => {
      if (event.name===eventName) {
        event.callback(data);
      }
    });
  }
  public removeEventListener(eventName: string, callback: () => any) {
    this.Listeners = this.Listeners.filter(event => event.name!==eventName);
  }
}

describe("Event emitter", () => {
  const emitter = new EventEmitter();
  const callback = jest.fn();
  test("adds a listener", () => {
    emitter.addEventListener("click", callback);
    expect(callback.mock.calls.length).toBe(0);
  });

  test("emits an event", () => {
    let sentEvent = {
      x: 123,
      y: 42,
    };
    emitter.trigger("click", sentEvent);

    expect(callback.mock.calls[0][0]).toBe(sentEvent);
  });

  test("removes the listener", () => {
    emitter.trigger("click");
    expect(callback.mock.calls.length).toBe(2);

    emitter.removeEventListener("click", callback);
    emitter.trigger("click");
    expect(callback.mock.calls.length).toBe(2);
  });
});