feat: add EventEmitter to Emitter and singleton paradigm

Signed-off-by: Remi Cattiau <remi@cattiau.com>

Author: loopingz

Diff for: src/event/cloudevent.ts

@@ -1,4 +1,5 @@
 import { v4 as uuidv4 } from "uuid";
+import { Emitter } from "..";
 
 import {
   CloudEventV03,
@@ -167,6 +168,16 @@ export class CloudEvent implements CloudEventV1, CloudEventV03 {
     }
   }
 
+  /**
+   * Emit this CloudEvent through the application
+   *
+   * @return {CloudEvent} current CloudEvent object
+   */
+  public emit(): this {
+    Emitter.emitEvent(this);
+    return this;
+  }
+
   /**
    * Clone a CloudEvent with new/update attributes
    * @param {object} options attributes to augment the CloudEvent with

Diff for: src/transport/emitter.ts

@@ -1,5 +1,6 @@
 import { CloudEvent } from "../event/cloudevent";
 import { HTTP, Message, Mode } from "../message";
+import { EventEmitter } from "events";
 
 /**
  * Options is an additional, optional dictionary of options that may
@@ -58,3 +59,44 @@ export function emitterFor(fn: TransportFunction, options = { binding: HTTP, mod
     }
   };
 }
+
+/**
+ * A static class to emit CloudEvents within an application
+ */
+export class Emitter extends EventEmitter {
+  /**
+   * Singleton store
+   */
+  static singleton: Emitter | undefined = undefined;
+
+  /**
+   * Create an Emitter
+   * On v4.0.0 this class will only remains as Singleton to allow using the
+   * EventEmitter of NodeJS
+   */
+  private constructor() {
+    super();
+  }
+
+  /**
+   * Return or create the Emitter singleton
+   *
+   * @return {Emitter} return Emitter singleton
+   */
+  static getSingleton(): Emitter {
+    if (!Emitter.singleton) {
+      Emitter.singleton = new Emitter();
+    }
+    return Emitter.singleton;
+  }
+
+  /**
+   * Emit an event inside this application
+   *
+   * @param {CloudEvent} event to emit
+   * @return {void}
+   */
+  static emitEvent(event: CloudEvent): void {
+    this.getSingleton().emit("event", event);
+  }
+}