[feat] 유저 saga 클래스 추가

Author: easdkr

src/user/saga/index.ts

@@ -0,0 +1 @@
+export * from './user.saga';

src/user/saga/user.saga.ts

@@ -0,0 +1,18 @@
+import { Injectable } from '@nestjs/common';
+import { ICommand, ofType, Saga } from '@nestjs/cqrs';
+import { map, Observable } from 'rxjs';
+import { CreateUserEvent } from '../event';
+import { CreateRegisterCouponCommand } from '../command';
+
+@Injectable()
+export class UserSaga {
+  /** @Saga() 가 있으면 애플리케이션의 이벤트 스트림을 구독하고 `ofType`으로 처리할 이벤트를 선택  */
+  @Saga()
+  public userCreated(event$: Observable<any>): Observable<ICommand> {
+    const fakeCouponId = 'fake-coupon-id';
+    return event$.pipe(
+      ofType(CreateUserEvent),
+      map((event) => new CreateRegisterCouponCommand(fakeCouponId, event.id)),
+    );
+  }
+}