feat(courses): reject enrollment in unpublished courses (BA-013)

BackendAcademy/src/courses/course.types.ts

@@ -17,7 +17,7 @@
  *   before starting Lesson 2").
  */
 
-// ── Course ──────────────────────────────────────────────────────────────────
+export type CourseStatus = 'draft' | 'published';
 
 export interface Course {
   courseId: string;
@@ -28,6 +28,8 @@ export interface Course {
    * can enrol in this course (e.g. ["ownership-101"] before "lifetimes-201").
    */
   prerequisiteCourseIds: string[];
+  /** Publication status: 'draft' | 'published'. Draft courses reject enrollment. */
+  status?: CourseStatus | string;
   createdAt: string;
 }
 
@@ -77,3 +79,8 @@ export interface PrerequisiteError {
   /** The specific prerequisite IDs that are not yet satisfied. */
   unmetPrerequisiteIds: string[];
 }
+
+export interface CourseNotPublishedError {
+  code: 'COURSE_NOT_PUBLISHED';
+  message: string;
+}

BackendAcademy/src/courses/enrollment.service.spec.ts

@@ -360,4 +360,42 @@ describe('EnrollmentService — prerequisite chains (BE-041)', () => {
       expect(enrollment.courseId).toBe('lifetimes-201');
     });
   });
+
+  // ── Course publication status (BA-013) ───────────────────────────────────
+
+  describe('course publication status (BA-013)', () => {
+    it('rejects enrollment in a draft course with 409 ConflictException', () => {
+      const course = makeCourse('rust-advanced-draft');
+      course.status = 'draft';
+
+      let caught: ConflictException | undefined;
+      try {
+        enrollmentService.enroll('user-1', 'rust-advanced-draft');
+      } catch (err) {
+        caught = err as ConflictException;
+      }
+
+      expect(caught).toBeInstanceOf(ConflictException);
+      expect(caught!.getStatus()).toBe(409);
+      const body = caught!.getResponse() as Record<string, unknown>;
+      expect(body.code).toBe('COURSE_NOT_PUBLISHED');
+      expect(typeof body.message).toBe('string');
+      expect(body.message).toContain('rust-advanced-draft');
+    });
+
+    it('allows enrollment in a published course', () => {
+      const course = makeCourse('rust-intro-published');
+      course.status = 'published';
+
+      const enrollment = enrollmentService.enroll('user-1', 'rust-intro-published');
+      expect(enrollment.courseId).toBe('rust-intro-published');
+      expect(enrollment.userId).toBe('user-1');
+    });
+
+    it('allows enrollment in a course when status is not explicitly set (defaults to allowed)', () => {
+      makeCourse('rust-standard-course');
+      const enrollment = enrollmentService.enroll('user-1', 'rust-standard-course');
+      expect(enrollment.courseId).toBe('rust-standard-course');
+    });
+  });
 });

BackendAcademy/src/courses/enrollment.service.ts

@@ -6,7 +6,7 @@ import {
 } from '@nestjs/common';
 import { CourseService } from './course.service';
 import { LessonService } from './lesson.service';
-import { Enrollment, LessonProgress, PrerequisiteError } from './course.types';
+import { CourseNotPublishedError, Enrollment, LessonProgress, PrerequisiteError } from './course.types';
 
 /**
  * Enrollment and lesson-progress service (BE-041).
@@ -64,6 +64,14 @@ export class EnrollmentService {
   enroll(userId: string, courseId: string): Enrollment {
     const course = this.courseService.findById(courseId);
 
+    if (course.status === 'draft') {
+      const errorPayload: CourseNotPublishedError = {
+        code: 'COURSE_NOT_PUBLISHED',
+        message: `Cannot enroll in draft course "${courseId}". Course is not published.`,
+      };
+      throw new ConflictException(errorPayload);
+    }
+
     const userEnrollments = this.enrollments.get(userId) ?? new Map<string, Enrollment>();
 
     if (userEnrollments.has(courseId)) {