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

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;
+  }
+}