xo-stack/packages/stack/tests/utils/event-emitter.spec.ts

import { describe, test, expect, vi, beforeEach } from 'vitest';
import { EventEmitter } from '../../src/utils/event-emitter.js';

type TestEvents = {
  test: { data: string };
  count: { value: number };
  multiPayload: { first: string; second: number };
};

describe('EventEmitter', () => {
  let emitter: EventEmitter<TestEvents>;

  beforeEach(() => {
    emitter = new EventEmitter<TestEvents>();
  });

  test('should register and trigger an event listener', () => {
    const mockCallback = vi.fn();
    emitter.on('test', mockCallback);

    emitter.emit('test', { data: 'hello' });

    expect(mockCallback).toHaveBeenCalledTimes(1);
    expect(mockCallback).toHaveBeenCalledWith({ data: 'hello' });
  });

  test('should register multiple listeners for the same event', () => {
    const mockCallback1 = vi.fn();
    const mockCallback2 = vi.fn();

    emitter.on('test', mockCallback1);
    emitter.on('test', mockCallback2);

    emitter.emit('test', { data: 'hello' });

    expect(mockCallback1).toHaveBeenCalledTimes(1);
    expect(mockCallback2).toHaveBeenCalledTimes(1);
  });

  test('should remove a specific listener', () => {
    const mockCallback1 = vi.fn();
    const mockCallback2 = vi.fn();

    emitter.on('test', mockCallback1);
    emitter.on('test', mockCallback2);

    emitter.off('test', mockCallback1);
    emitter.emit('test', { data: 'hello' });

    expect(mockCallback1).not.toHaveBeenCalled();
    expect(mockCallback2).toHaveBeenCalledTimes(1);
  });

  test('should remove all listeners when removeAllListeners is called', () => {
    const mockCallback1 = vi.fn();
    const mockCallback2 = vi.fn();

    emitter.on('test', mockCallback1);
    emitter.on('count', mockCallback2);

    emitter.removeAllListeners();

    emitter.emit('test', { data: 'hello' });
    emitter.emit('count', { value: 42 });

    expect(mockCallback1).not.toHaveBeenCalled();
    expect(mockCallback2).not.toHaveBeenCalled();
  });

  test('should call listener only once when using once', () => {
    const mockCallback = vi.fn();

    emitter.once('test', mockCallback);

    emitter.emit('test', { data: 'first' });
    emitter.emit('test', { data: 'second' });

    expect(mockCallback).toHaveBeenCalledTimes(1);
    expect(mockCallback).toHaveBeenCalledWith({ data: 'first' });
  });

  test('should handle multiple event types correctly', () => {
    const testCallback = vi.fn();
    const countCallback = vi.fn();

    emitter.on('test', testCallback);
    emitter.on('count', countCallback);

    emitter.emit('test', { data: 'test data' });
    emitter.emit('count', { value: 123 });

    expect(testCallback).toHaveBeenCalledWith({ data: 'test data' });
    expect(countCallback).toHaveBeenCalledWith({ value: 123 });
  });

  test('should debounce events correctly', async () => {
    vi.useFakeTimers();
    const mockCallback = vi.fn();

    emitter.on('test', mockCallback, 100);

    emitter.emit('test', { data: 'first' });
    emitter.emit('test', { data: 'second' });
    emitter.emit('test', { data: 'third' });

    expect(mockCallback).not.toHaveBeenCalled();

    await vi.runAllTimersAsync();

    expect(mockCallback).toHaveBeenCalledTimes(1);
    expect(mockCallback).toHaveBeenCalledWith({ data: 'third' });

    vi.useRealTimers();
  });

  test('should handle complex payloads', () => {
    const mockCallback = vi.fn();

    emitter.on('multiPayload', mockCallback);

    const payload = { first: 'hello', second: 42 };
    emitter.emit('multiPayload', payload);

    expect(mockCallback).toHaveBeenCalledWith(payload);
  });

  test('should return true when event has listeners and false when it does not', () => {
    const mockCallback = vi.fn();

    expect(emitter.emit('test', { data: 'hello' })).toBe(false);

    emitter.on('test', mockCallback);

    expect(emitter.emit('test', { data: 'hello' })).toBe(true);
  });

  test('should handle debounced once events correctly', async () => {
    vi.useFakeTimers();
    const mockCallback = vi.fn();

    emitter.once('test', mockCallback, 100);

    emitter.emit('test', { data: 'first' });
    emitter.emit('test', { data: 'second' });
    emitter.emit('test', { data: 'third' });

    expect(mockCallback).not.toHaveBeenCalled();

    await vi.runAllTimersAsync();

    expect(mockCallback).toHaveBeenCalledTimes(1);
    expect(mockCallback).toHaveBeenCalledWith({ data: 'third' });

    // Emit again after debounce
    emitter.emit('test', { data: 'fourth' });

    await vi.runAllTimersAsync();

    expect(mockCallback).toHaveBeenCalledTimes(1);

    vi.useRealTimers();
  });

  test('waitFor should resolve when predicate is satisfied', async () => {
    const promise = emitter.waitFor(
      'test',
      (payload) => payload.data === 'success',
    );

    emitter.emit('test', { data: 'not yet' });
    emitter.emit('test', { data: 'success' });

    const result = await promise;
    expect(result).toEqual({ data: 'success' });
  });

  test('waitFor should reject on timeout', async () => {
    vi.useFakeTimers();

    const promise = emitter.waitFor(
      'test',
      (payload) => payload.data === 'success',
      1000,
    );

    // Need to handle the rejection or wait for it
    const promiseResult = promise.catch((error) => {
      expect(error.message).toBe('Timeout waiting for event "test"');
    });

    emitter.emit('test', { data: 'not yet' });

    await vi.runAllTimersAsync();
    await promiseResult;

    vi.useRealTimers();
  });

  test('waitFor should clean up listeners after resolution', async () => {
    const promise = emitter.waitFor(
      'test',
      (payload) => payload.data === 'success',
    );

    emitter.emit('test', { data: 'success' });
    await promise;

    // The internal listener should be removed
    expect(emitter.emit('test', { data: 'another' })).toBe(false);
  });

  test('waitFor should handle multiple concurrent waits', async () => {
    const promise1 = emitter.waitFor(
      'test',
      (payload) => payload.data === 'first',
    );
    const promise2 = emitter.waitFor(
      'test',
      (payload) => payload.data === 'second',
    );

    emitter.emit('test', { data: 'second' });
    emitter.emit('test', { data: 'first' });

    const [result1, result2] = await Promise.all([promise1, promise2]);

    expect(result1).toEqual({ data: 'first' });
    expect(result2).toEqual({ data: 'second' });
  });

  test('waitFor should clean up timeout on successful resolution', async () => {
    vi.useFakeTimers();

    const promise = emitter.waitFor(
      'test',
      (payload) => payload.data === 'success',
      1000,
    );

    // Emit success before timeout
    emitter.emit('test', { data: 'success' });

    // Fast-forward time - should not cause rejection
    await vi.runAllTimersAsync();

    const result = await promise;
    expect(result).toEqual({ data: 'success' });

    vi.useRealTimers();
  });
});