trackgo-fe/packages/core-events/src/event-bus.test.ts

import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
import { renderHook, act } from '@testing-library/react';
import { eventBus, publish, subscribe } from './event-bus';
import { useAppEvent, usePublishEvent } from './hooks';

// ─── Test-Local Event Augmentation ──────────────────────────────
//
// In a real app, these would live in a `.d.ts` file inside the app's
// `src/types/` folder using `declare module '@repo/core-events'`.
//
// For the core package's own test suite, we augment the registry
// directly here so the tests have concrete event types to work with
// without polluting the core's shipped types.
//
declare module './events.registry' {
  interface AppEventRegistry {
    'TEST:STOCK_UPDATE': StockUpdatePayload;
    'TEST:PROFILE_UPDATED': ProfileUpdatedPayload;
    'TEST:INITIALIZED': undefined;
  }
}

// ─── Test Payload Types ─────────────────────────────────────────

interface StockUpdatePayload {
  id: string;
  price: number;
  change: number;
  volume: number;
}

interface ProfileUpdatedPayload {
  id: string;
  name: string;
  email: string;
  avatar: string;
  updatedAt: number;
}

// ─── Helpers ────────────────────────────────────────────────────

/** Clear all mitt handlers between tests to avoid cross-contamination. */
function clearAllHandlers() {
  eventBus.all.clear();
}

// ─── Test Data ──────────────────────────────────────────────────

const mockStockUpdate: StockUpdatePayload = {
  id: 'AAPL',
  price: 185.42,
  change: 1.23,
  volume: 50000,
};

const mockProfile: ProfileUpdatedPayload = {
  id: 'user-1',
  name: 'Firman',
  email: 'firman@eigen.co.id',
  avatar: 'https://example.com/avatar.png',
  updatedAt: Date.now(),
};

// ─── Core Event Bus Tests ───────────────────────────────────────

describe('Event Bus (Core)', () => {
  beforeEach(() => {
    clearAllHandlers();
  });

  afterEach(() => {
    clearAllHandlers();
  });

  it('publishes and subscribes to a typed event', () => {
    const handler = vi.fn();

    subscribe('TEST:STOCK_UPDATE', handler);
    publish('TEST:STOCK_UPDATE', mockStockUpdate);

    expect(handler).toHaveBeenCalledTimes(1);
    expect(handler).toHaveBeenCalledWith(mockStockUpdate);
  });

  it('delivers events to multiple subscribers', () => {
    const handler1 = vi.fn();
    const handler2 = vi.fn();

    subscribe('TEST:PROFILE_UPDATED', handler1);
    subscribe('TEST:PROFILE_UPDATED', handler2);
    publish('TEST:PROFILE_UPDATED', mockProfile);

    expect(handler1).toHaveBeenCalledTimes(1);
    expect(handler2).toHaveBeenCalledTimes(1);
  });

  it('does not deliver events to unrelated subscribers', () => {
    const stockHandler = vi.fn();
    const profileHandler = vi.fn();

    subscribe('TEST:STOCK_UPDATE', stockHandler);
    subscribe('TEST:PROFILE_UPDATED', profileHandler);

    publish('TEST:STOCK_UPDATE', mockStockUpdate);

    expect(stockHandler).toHaveBeenCalledTimes(1);
    expect(profileHandler).not.toHaveBeenCalled();
  });

  it('unsubscribes correctly via returned function', () => {
    const handler = vi.fn();

    const unsub = subscribe('TEST:STOCK_UPDATE', handler);

    publish('TEST:STOCK_UPDATE', mockStockUpdate);
    expect(handler).toHaveBeenCalledTimes(1);

    // Unsubscribe
    unsub();

    publish('TEST:STOCK_UPDATE', mockStockUpdate);
    // Should still be 1, not 2
    expect(handler).toHaveBeenCalledTimes(1);
  });

  it('handles events with undefined payloads', () => {
    const handler = vi.fn();

    subscribe('TEST:INITIALIZED', handler);
    publish('TEST:INITIALIZED', undefined);

    expect(handler).toHaveBeenCalledTimes(1);
    expect(handler).toHaveBeenCalledWith(undefined);
  });

  it('handles rapid-fire events without loss', () => {
    const handler = vi.fn();
    subscribe('TEST:STOCK_UPDATE', handler);

    for (let i = 0; i < 1000; i++) {
      publish('TEST:STOCK_UPDATE', { ...mockStockUpdate, id: `STOCK-${i}` });
    }

    expect(handler).toHaveBeenCalledTimes(1000);
  });
});

// ─── React Hook Tests ───────────────────────────────────────────

describe('useAppEvent (React Hook)', () => {
  beforeEach(() => {
    clearAllHandlers();
  });

  afterEach(() => {
    clearAllHandlers();
  });

  it('subscribes on mount and receives events', () => {
    const handler = vi.fn();

    renderHook(() => useAppEvent('TEST:STOCK_UPDATE', handler));

    act(() => {
      publish('TEST:STOCK_UPDATE', mockStockUpdate);
    });

    expect(handler).toHaveBeenCalledTimes(1);
    expect(handler).toHaveBeenCalledWith(mockStockUpdate);
  });

  it('unsubscribes on unmount — MEMORY LEAK PREVENTION', () => {
    const handler = vi.fn();

    const { unmount } = renderHook(() => useAppEvent('TEST:STOCK_UPDATE', handler));

    // Event should be received while mounted
    act(() => {
      publish('TEST:STOCK_UPDATE', mockStockUpdate);
    });
    expect(handler).toHaveBeenCalledTimes(1);

    // Unmount the component
    unmount();

    // Event should NOT be received after unmount
    act(() => {
      publish('TEST:STOCK_UPDATE', mockStockUpdate);
    });

    // Still 1, proving the handler was properly cleaned up
    expect(handler).toHaveBeenCalledTimes(1);
  });

  it('does not leak handlers across mount/unmount cycles', () => {
    const handler = vi.fn();

    // Mount and unmount 100 times
    for (let i = 0; i < 100; i++) {
      const { unmount } = renderHook(() => useAppEvent('TEST:STOCK_UPDATE', handler));
      unmount();
    }

    // After 100 cycles, emit one event
    act(() => {
      publish('TEST:STOCK_UPDATE', mockStockUpdate);
    });

    // Should be 0 — all handlers should have been cleaned up
    expect(handler).toHaveBeenCalledTimes(0);

    // Verify the handler map is empty for this event type
    const handlers = eventBus.all.get('TEST:STOCK_UPDATE');
    expect(!handlers || handlers.length === 0).toBe(true);
  });

  it('always calls the latest handler (no stale closures)', () => {
    let capturedValue = '';

    const { rerender } = renderHook(
      ({ value }: { value: string }) =>
        useAppEvent('TEST:PROFILE_UPDATED', () => {
          capturedValue = value;
        }),
      { initialProps: { value: 'initial' } },
    );

    // Update the closure value
    rerender({ value: 'updated' });

    act(() => {
      publish('TEST:PROFILE_UPDATED', mockProfile);
    });

    // Should capture the LATEST value, not the stale 'initial'
    expect(capturedValue).toBe('updated');
  });

  it('does not re-subscribe when handler reference changes', () => {
    // We spy on eventBus.on to count subscription calls
    const onSpy = vi.spyOn(eventBus, 'on');
    const offSpy = vi.spyOn(eventBus, 'off');

    const { rerender } = renderHook(
      ({ handler }: { handler: () => void }) =>
        useAppEvent('TEST:INITIALIZED', handler),
      { initialProps: { handler: vi.fn() } },
    );

    const initialOnCount = onSpy.mock.calls.length;
    const initialOffCount = offSpy.mock.calls.length;

    // Re-render with a NEW handler function reference
    rerender({ handler: vi.fn() });

    // on/off should NOT have been called again (ref-based pattern)
    expect(onSpy.mock.calls.length).toBe(initialOnCount);
    expect(offSpy.mock.calls.length).toBe(initialOffCount);

    onSpy.mockRestore();
    offSpy.mockRestore();
  });
});

describe('usePublishEvent (React Hook)', () => {
  beforeEach(() => {
    clearAllHandlers();
  });

  afterEach(() => {
    clearAllHandlers();
  });

  it('returns a working publish function', () => {
    const handler = vi.fn();
    subscribe('TEST:PROFILE_UPDATED', handler);

    const { result } = renderHook(() => usePublishEvent());

    act(() => {
      result.current('TEST:PROFILE_UPDATED', mockProfile);
    });

    expect(handler).toHaveBeenCalledTimes(1);
    expect(handler).toHaveBeenCalledWith(mockProfile);
  });

  it('returns a referentially stable function across re-renders', () => {
    const { result, rerender } = renderHook(() => usePublishEvent());

    const firstRef = result.current;

    rerender();
    rerender();
    rerender();

    expect(result.current).toBe(firstRef);
  });
});