feat(packages/stdlib): add PubSub class and tests to patterns

packages/stdlib/src/patterns/behavioral/pubsub/index.test.ts

@@ -0,0 +1,95 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { PubSub } from './index';
+
+describe('PubSub', () => {
+  let eventBus: PubSub<{
+    event1: (arg: string) => void;
+    event2: () => void
+  }>;
+
+  beforeEach(() => {
+    eventBus = new PubSub();
+  });
+
+  it('add a listener and emit an event', () => {
+    const listener = vi.fn();
+
+    eventBus.on('event1', listener);
+    eventBus.emit('event1', 'Hello');
+
+    expect(listener).toHaveBeenCalledWith('Hello');
+  });
+
+  it('add multiple listeners and emit an event', () => {
+    const listener1 = vi.fn();
+    const listener2 = vi.fn();
+
+    eventBus.on('event1', listener1);
+    eventBus.on('event1', listener2);
+    eventBus.emit('event1', 'Hello');
+
+    expect(listener1).toHaveBeenCalledWith('Hello');
+    expect(listener2).toHaveBeenCalledWith('Hello');
+  });
+
+  it('add a one-time listener and emit an event', () => {
+    const listener = vi.fn();
+
+    eventBus.once('event1', listener);
+    eventBus.emit('event1', 'Hello');
+    eventBus.emit('event1', 'World');
+
+    expect(listener).toHaveBeenCalledWith('Hello');
+    expect(listener).not.toHaveBeenCalledWith('World');
+  });
+
+  it('add once listener and emit multiple events', () => {
+    const listener = vi.fn();
+
+    eventBus.once('event1', listener);
+    eventBus.emit('event1', 'Hello');
+    eventBus.emit('event1', 'World');
+    eventBus.emit('event1', '!');
+
+    expect(listener).toHaveBeenCalledTimes(1);
+    expect(listener).toHaveBeenCalledWith('Hello');
+  });
+
+  it('remove a listener', () => {
+    const listener = vi.fn();
+
+    eventBus.on('event1', listener);
+    eventBus.off('event1', listener);
+    eventBus.emit('event1', 'Hello');
+
+    expect(listener).not.toHaveBeenCalled();
+  });
+
+  it('clear all listeners for an event', () => {
+    const listener1 = vi.fn();
+    const listener2 = vi.fn();
+
+    eventBus.on('event1', listener1);
+    eventBus.on('event1', listener2);
+    eventBus.clear('event1');
+    eventBus.emit('event1', 'Hello');
+
+    expect(listener1).not.toHaveBeenCalled();
+    expect(listener2).not.toHaveBeenCalled();
+  });
+
+  it('return true when emitting an event with listeners', () => {
+    const listener = vi.fn();
+
+    eventBus.on('event1', listener);
+    const result = eventBus.emit('event1', 'Hello');
+
+    expect(result).toBe(true);
+  });
+
+  it('return false when emitting an event without listeners', () => {
+    const result = eventBus.emit('event1', 'Hello');
+
+    expect(result).toBe(false);
+  });
+});

packages/stdlib/src/patterns/behavioral/pubsub/index.ts

@@ -0,0 +1,58 @@
+export type Subscriber = (...args: any[]) => void;
+export type EventsRecord = Record<string, Subscriber>;
+
+export class PubSub<Events extends EventsRecord> {
+  private events: Map<keyof Events, Set<Events[keyof Events]>>;
+
+  constructor() {
+    this.events = new Map();
+  }
+
+  public on<K extends keyof Events>(event: K, listener: Events[K]) {
+    const listeners = this.events.get(event);
+
+    if (listeners)
+      listeners.add(listener);
+    else
+      this.events.set(event, new Set([listener]));
+
+    return this;
+  }
+
+  public off<K extends keyof Events>(event: K, listener: Events[K]) {
+    const listeners = this.events.get(event);
+
+    if (listeners)
+      listeners.delete(listener);
+
+    return this;
+  }
+
+  public once<K extends keyof Events>(event: K, listener: Events[K]) {
+    const onceListener = (...args: Parameters<Events[K]>) => {
+        this.off(event, onceListener as Events[K]);
+        listener(...args);
+    };
+
+    this.on(event, onceListener as Events[K]);
+
+    return this;
+  }
+
+  public emit<K extends keyof Events>(event: K, ...args: Parameters<Events[K]>): boolean {
+    const listeners = this.events.get(event);
+
+    if (!listeners)
+      return false;
+
+    listeners.forEach((listener) => listener(...args));
+
+    return true;
+  }
+
+  public clear<K extends keyof Events>(event: K) {
+    this.events.delete(event);
+
+    return this;
+  }
+}