Set as async the interfaces that will be async in the future implementations. Add Nullable type

Author: vilasmaciel

src/Contexts/Mooc/Courses/application/CreateCourse.ts

@@ -11,6 +11,6 @@ export default class CreateCourse {
   async run(id: string, name: string, duration: string): Promise<void> {
     const course = new Course(id, name, duration);
 
-    this.repository.save(course);
+    return this.repository.save(course);
   }
 }

src/Contexts/Mooc/Courses/domain/CourseRepository.ts

@@ -1,7 +1,8 @@
 import Course from './Course';
+import { Nullable } from '../../../Shared/domain/Nullable';
 
 export default interface CourseRepository {
-  save(course: Course): Promise<void> | void;
+  save(course: Course): Promise<void>;
 
-  search(id: string): Promise<Course> | Course;
+  search(id: string): Promise<Nullable<Course>>;
 }

src/Contexts/Mooc/Courses/infrastructure/FileCourseRepository.ts

@@ -1,17 +1,24 @@
 import CourseRepository from '../domain/CourseRepository';
 import Course from '../domain/Course';
-import * as fs from 'fs';
+import fs from 'fs';
 import BSON from 'bson';
+import { Nullable } from '../../../Shared/domain/Nullable';
 
 export default class FileCourseRepository implements CourseRepository {
   private FILE_PATH = `${__dirname}/courses`;
 
-  save(course: Course): void | Promise<void> {
-    fs.writeFileSync(this.filePath(course.id), BSON.serialize(course));
+  async save(course: Course): Promise<void> {
+    const filePath = this.filePath(course.id);
+    const data = BSON.serialize(course);
+
+   return fs.writeFileSync(filePath, data);
   }
 
-  search(id: string): Course {
-    return fs.existsSync(this.filePath(id)) ? BSON.deserialize(fs.readFileSync(this.filePath(id))) : null;
+  async search(id: string): Promise<Nullable<Course>> {
+    const filePath = this.filePath(id);
+    const exists = fs.existsSync(filePath);
+
+    return exists ? BSON.deserialize(fs.readFileSync(this.filePath(id))) : null;
   }
 
   private filePath(id: string): string {

src/Contexts/Shared/domain/Nullable.ts

@@ -0,0 +1 @@
+export type Nullable<T> = T | null;