feat(plugins): add EventBus with typed events and crash-safe handlers

Amit Haridas

src/plugins/event-bus.js

@@ -0,0 +1,43 @@
+class EventBus {
+  constructor() {
+    this.listeners = new Map();
+  }
+
+  on(event, handler) {
+    if (!this.listeners.has(event)) {
+      this.listeners.set(event, []);
+    }
+    this.listeners.get(event).push(handler);
+  }
+
+  off(event, handler) {
+    if (!handler) {
+      this.listeners.delete(event);
+      return;
+    }
+    const handlers = this.listeners.get(event);
+    if (handlers) {
+      const idx = handlers.indexOf(handler);
+      if (idx !== -1) handlers.splice(idx, 1);
+    }
+  }
+
+  emit(event, payload) {
+    const handlers = this.listeners.get(event);
+    if (!handlers) return;
+    for (const handler of handlers) {
+      try {
+        handler(payload);
+      } catch (err) {
+        console.error(`[EventBus] Error in handler for "${event}":`, err);
+      }
+    }
+  }
+
+  hasHandler(event) {
+    const handlers = this.listeners.get(event);
+    return handlers != null && handlers.length > 0;
+  }
+}
+
+module.exports = { EventBus };

tests/event-bus.test.js

@@ -0,0 +1,64 @@
+const { EventBus } = require('../src/plugins/event-bus');
+
+describe('EventBus', () => {
+  let bus;
+
+  beforeEach(() => {
+    bus = new EventBus();
+  });
+
+  test('on/emit — listener receives payload', () => {
+    const received = [];
+    bus.on('document:saved', (payload) => received.push(payload));
+    bus.emit('document:saved', { filePath: '/test.md', tabId: 'tab1' });
+    expect(received).toEqual([{ filePath: '/test.md', tabId: 'tab1' }]);
+  });
+
+  test('on — ignores events with no listeners', () => {
+    expect(() => bus.emit('unknown:event', {})).not.toThrow();
+  });
+
+  test('off — removes specific listener', () => {
+    const handler = jest.fn();
+    bus.on('test:event', handler);
+    bus.off('test:event', handler);
+    bus.emit('test:event', {});
+    expect(handler).not.toHaveBeenCalled();
+  });
+
+  test('off — removes all listeners for event when no handler given', () => {
+    const h1 = jest.fn();
+    const h2 = jest.fn();
+    bus.on('test:event', h1);
+    bus.on('test:event', h2);
+    bus.off('test:event');
+    bus.emit('test:event', {});
+    expect(h1).not.toHaveBeenCalled();
+    expect(h2).not.toHaveBeenCalled();
+  });
+
+  test('hasHandler — returns true when listener exists', () => {
+    bus.on('ai:analyze', () => {});
+    expect(bus.hasHandler('ai:analyze')).toBe(true);
+  });
+
+  test('hasHandler — returns false when no listener exists', () => {
+    expect(bus.hasHandler('ai:analyze')).toBe(false);
+  });
+
+  test('handler errors are caught and logged, not thrown', () => {
+    const errorSpy = jest.spyOn(console, 'error').mockImplementation(() => {});
+    bus.on('bad:event', () => { throw new Error('boom'); });
+    expect(() => bus.emit('bad:event', {})).not.toThrow();
+    expect(errorSpy).toHaveBeenCalled();
+    errorSpy.mockRestore();
+  });
+
+  test('multiple listeners all receive the event', () => {
+    const results = [];
+    bus.on('multi:event', () => results.push('a'));
+    bus.on('multi:event', () => results.push('b'));
+    bus.emit('multi:event', {});
+    expect(results).toEqual(['a', 'b']);
+  });
+});