feat: add EventEmitter to Emitter and singleton paradigm

Author: loopingz

src/event/cloudevent.ts

@@ -1,4 +1,5 @@
 import { v4 as uuidv4 } from "uuid";
+import { Emitter } from "..";
 
 import {
   CloudEventV03,
@@ -167,6 +168,14 @@ export class CloudEvent implements CloudEventV1, CloudEventV03 {
     }
   }
 
+  /**
+   * Emit this CloudEvent through the application
+   */
+  public emit(): this {
+    Emitter.emit(this);
+    return this;
+  }
+
   /**
    * Clone a CloudEvent with new/update attributes
    * @param {object} options attributes to augment the CloudEvent with

src/transport/emitter.ts

@@ -91,15 +91,29 @@ export function emitterFor(fn: TransportFunction, options = { binding: HTTP, mod
  *
  * @see https://github.com/cloudevents/spec/blob/v1.0/http-protocol-binding.md
  * @see https://github.com/cloudevents/spec/blob/v1.0/http-protocol-binding.md#13-content-modes
- * @deprecated Will be removed in 4.0.0. Consider using the emitterFactory
  *
  */
-export class Emitter {
+export class Emitter extends EventEmitter {
+  /**
+   * Singleton store
+   */
+  static singleton: Emitter = undefined;
   url?: string;
   protocol: Protocol;
   binaryEmitter: EmitterFunction;
   structuredEmitter: EmitterFunction;
 
+  /**
+   * Create an Emitter
+   * On v4.0.0 this class will only remains as Singleton to allow using the
+   * EventEmitter of NodeJS
+   *
+   *
+   * @param {Object} [options] The configuration options for this event. Options
+   * provided will be passed along to Node.js `http.request()`.
+   * https://nodejs.org/api/http.html#http_http_request_options_callback
+   * @deprecated Will be removed in 4.0.0. Consider using the emitterFactory
+   */
   constructor(options: TransportOptions = { protocol: Protocol.HTTPBinary }) {
     this.protocol = options.protocol as Protocol;
     this.url = options.url;
@@ -131,4 +145,23 @@ export class Emitter {
     }
     return this.binaryEmitter(event, options);
   }
+
+  /**
+   * Return or create the Emitter singleton
+   */
+  static getSingleton() {
+    if (!Emitter.singleton) {
+      Emitter.singleton = new Emitter();
+    }
+    return Emitter.singleton;
+  }
+
+  /**
+   * Emit an event inside this application
+   *
+   * @param event to emit
+   */
+  static emit(event: CloudEvent) {
+    this.getSingleton().emit("event", event);
+  }
 }