oO/services/api/src/events/__tests__/bus.test.ts

import { describe, it, expect, vi } from 'vitest';
import { Bus, bus } from '../bus.js';

// Use a fresh Bus instance for isolation in most tests
function makeBus() {
  return new Bus();
}

describe('EventBus — delivery', () => {
  it('delivers a published event to subscribers', () => {
    const b = makeBus();
    const handler = vi.fn();
    b.subscribe('signals.tip.served', handler);

    const payload = { userId: 'u1', tipId: 'tip:1', policy: 'random', servedAt: new Date().toISOString() };
    b.publish('signals.tip.served', payload);

    expect(handler).toHaveBeenCalledOnce();
    expect(handler).toHaveBeenCalledWith(payload);
  });

  it('delivers to multiple subscribers on the same subject', () => {
    const b = makeBus();
    const h1 = vi.fn();
    const h2 = vi.fn();
    b.subscribe('signals.tip.served', h1);
    b.subscribe('signals.tip.served', h2);

    b.publish('signals.tip.served', { userId: 'u', tipId: 't', policy: 'p', servedAt: '' });

    expect(h1).toHaveBeenCalledOnce();
    expect(h2).toHaveBeenCalledOnce();
  });

  it('does not deliver to handlers on a different subject', () => {
    const b = makeBus();
    const feedbackHandler = vi.fn();
    b.subscribe('signals.tip.feedback', feedbackHandler);

    b.publish('signals.tip.served', { userId: 'u', tipId: 't', policy: 'p', servedAt: '' });

    expect(feedbackHandler).not.toHaveBeenCalled();
  });

  it('does not call a handler after bus.off()', () => {
    const b = makeBus();
    const handler = vi.fn();
    b.subscribe('signals.tip.served', handler);
    b.off('signals.tip.served', handler);

    b.publish('signals.tip.served', { userId: 'u', tipId: 't', policy: 'p', servedAt: '' });

    expect(handler).not.toHaveBeenCalled();
  });

  it('does not throw when publishing with no subscribers', () => {
    const b = makeBus();
    expect(() =>
      b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 3, syncedAt: '' }),
    ).not.toThrow();
  });

  it('reward maps correctly: done=1, dismiss=-1, snooze=0', () => {
    const b = makeBus();
    const cases: Array<['done' | 'dismiss' | 'snooze', number]> = [
      ['done', 1.0],
      ['dismiss', -1.0],
      ['snooze', 0.0],
    ];

    for (const [action, expected] of cases) {
      const handler = vi.fn();
      b.subscribe('signals.tip.feedback', handler);

      const payload = {
        userId: 'u1',
        tipId: 'todoist:42',
        action,
        reward: action === 'done' ? 1.0 : action === 'dismiss' ? -1.0 : 0.0,
        dwellMs: null,
        createdAt: new Date().toISOString(),
      };
      b.publish('signals.tip.feedback', payload);

      expect(handler).toHaveBeenCalledWith(expect.objectContaining({ reward: expected }));
      b.off('signals.tip.feedback', handler);
    }
  });
});

describe('EventBus — ring buffer / tail()', () => {
  it('tail() returns published events', () => {
    const b = makeBus();
    b.publish('signals.tip.served', { userId: 'u1', tipId: 't1', policy: 'p', servedAt: '' });
    b.publish('signals.tip.served', { userId: 'u2', tipId: 't2', policy: 'p', servedAt: '' });

    const events = b.tail();
    expect(events.length).toBeGreaterThanOrEqual(2);
  });

  it('tail() filters by subject prefix', () => {
    const b = makeBus();
    b.publish('signals.tip.served', { userId: 'u', tipId: 't', policy: 'p', servedAt: '' });
    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 1, syncedAt: '' });

    const tipEvents = b.tail({ subject: 'signals.tip' });
    expect(tipEvents.every((e) => e.subject.startsWith('signals.tip'))).toBe(true);

    const taskEvents = b.tail({ subject: 'signals.task' });
    expect(taskEvents.every((e) => e.subject.startsWith('signals.task'))).toBe(true);
  });

  it('tail() filters by userId', () => {
    const b = makeBus();
    b.publish('signals.tip.served', { userId: 'alice', tipId: 't1', policy: 'p', servedAt: '' });
    b.publish('signals.tip.served', { userId: 'bob', tipId: 't2', policy: 'p', servedAt: '' });

    const aliceEvents = b.tail({ userId: 'alice' });
    expect(aliceEvents.every((e) => (e.payload as any).userId === 'alice')).toBe(true);
  });

  it('tail() respects limit', () => {
    const b = makeBus();
    for (let i = 0; i < 10; i++) {
      b.publish('signals.tip.served', { userId: 'u', tipId: `t${i}`, policy: 'p', servedAt: '' });
    }
    const events = b.tail({ limit: 3 });
    expect(events).toHaveLength(3);
  });

  it('tail() returns only events after `since` id', () => {
    const b = makeBus();
    b.publish('signals.tip.served', { userId: 'u', tipId: 't1', policy: 'p', servedAt: '' });
    const snap = b.tail();
    const lastId = snap[snap.length - 1].id;

    b.publish('signals.tip.served', { userId: 'u', tipId: 't2', policy: 'p', servedAt: '' });

    const after = b.tail({ since: lastId });
    expect(after).toHaveLength(1);
    expect((after[0].payload as any).tipId).toBe('t2');
  });

  it('assigns monotonically increasing ids', () => {
    const b = makeBus();
    b.publish('signals.tip.served', { userId: 'u', tipId: 't1', policy: 'p', servedAt: '' });
    b.publish('signals.tip.served', { userId: 'u', tipId: 't2', policy: 'p', servedAt: '' });

    const events = b.tail();
    const ids = events.map((e) => e.id);
    for (let i = 1; i < ids.length; i++) {
      expect(ids[i]).toBeGreaterThan(ids[i - 1]);
    }
  });

  it('ring buffer caps at 500 entries and evicts oldest', () => {
    const b = makeBus();
    // Publish 502 events — the first two should be evicted
    for (let i = 0; i < 502; i++) {
      b.publish('signals.tip.served', { userId: 'u', tipId: `t${i}`, policy: 'p', servedAt: '' });
    }
    const all = b.tail({ limit: 1000 });
    expect(all).toHaveLength(500);
    // Oldest surviving entry should be the 3rd published (index 2)
    expect((all[0].payload as any).tipId).toBe('t2');
  });
});

describe('EventBus — singleton bus export', () => {
  it('singleton bus is a Bus instance', () => {
    expect(bus).toBeInstanceOf(Bus);
  });
});

describe('EventBus — onPublish hook (NATS bridge contract)', () => {
  it('invokes registered hook with subject + payload on every publish', () => {
    const b = makeBus();
    const hook = vi.fn();
    b.onPublish(hook);

    const payload = { userId: 'u', source: 'todoist', count: 2, syncedAt: 'now' };
    b.publish('signals.task.synced', payload);

    expect(hook).toHaveBeenCalledOnce();
    expect(hook).toHaveBeenCalledWith('signals.task.synced', payload);
  });

  it('fires multiple hooks in registration order', () => {
    const b = makeBus();
    const calls: string[] = [];
    b.onPublish(() => calls.push('a'));
    b.onPublish(() => calls.push('b'));

    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 0, syncedAt: '' });
    expect(calls).toEqual(['a', 'b']);
  });

  it('hook fires alongside subscribers — both receive the publish', () => {
    const b = makeBus();
    const hook = vi.fn();
    const sub = vi.fn();
    b.onPublish(hook);
    b.subscribe('signals.task.synced', sub);

    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 1, syncedAt: '' });
    expect(hook).toHaveBeenCalledOnce();
    expect(sub).toHaveBeenCalledOnce();
  });

  it('a throwing hook still bubbles up — bus does not silently swallow', () => {
    // Documents current behaviour: hooks run inside publish(), so a thrown
    // error escapes. The NATS adapter therefore catches inside the hook.
    const b = makeBus();
    b.onPublish(() => {
      throw new Error('boom');
    });
    expect(() =>
      b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 0, syncedAt: '' }),
    ).toThrow('boom');
  });
});