Added initial decorator for wiring up events

ghost/core/core/boot.js

@@ -404,6 +404,9 @@ async function initNestDependencies() {
     }, {
         provide: 'urlUtils',
         useValue: urlUtils
+    }, {
+        provide: 'DomainEvents',
+        useValue: require('@tryghost/domain-events')
     }, {
         provide: 'urlUtilsHax',
         useValue: {

ghost/ghost/src/common/handle-event.decorator.ts

@@ -0,0 +1,40 @@
+import {NestApplication} from '@nestjs/core';
+
+interface IEvent<T> {
+    data: T
+    timestamp: Date
+}
+
+interface IDomainEvents {
+    subscribe<T>(event: new (data: T, timestamp: Date) => IEvent<T>, fn: (_event: IEvent<T>) => void): void;
+    dispatch<T>(event: IEvent<T>): void
+}
+
+type EventRegistrationSpec<EventData, Subscriber> = {
+    Event: new (data: EventData, timestamp: Date) => IEvent<EventData>,
+    target: new (...args: unknown[]) => Subscriber,
+    methodName: string
+};
+
+const events: EventRegistrationSpec<unknown, unknown>[] = [];
+
+export function HandleEvent<T>(Event: new (data: T, timestamp: Date) => IEvent<T>) {
+    return function (target: object, methodName: string) {
+        events.push({
+            Event: Event as new (data: unknown, timestamp: Date) => IEvent<T>,
+            target: target.constructor as new (...args: unknown[]) => unknown,
+            methodName
+        });
+    };
+}
+
+export function registerEvents(app: NestApplication, DomainEvents: IDomainEvents) {
+    for (const eventSpec of events) {
+        DomainEvents.subscribe(eventSpec.Event, async function (event: IEvent<unknown>) {
+            // We have to cast to `any` here because we don't know the type - but we do know that it should have the `methodName` method
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            const service = await app.resolve(eventSpec.target) as any;
+            await service[eventSpec.methodName](event);
+        });
+    }
+}

ghost/ghost/src/index.ts

@@ -1,9 +1,12 @@
 import 'reflect-metadata';
 import {AppModule} from './nestjs/AppModule';
-import {NestFactory} from '@nestjs/core';
+import {NestApplication, NestFactory} from '@nestjs/core';
+import {registerEvents} from './common/handle-event.decorator';
 
 export async function create() {
     const app = await NestFactory.create(AppModule);
+    const DomainEvents = await app.resolve('DomainEvents');
+    registerEvents(app as NestApplication, DomainEvents);
     return app;
 }