fix: validate and deduplicate course progress

[Jidnyasa-P]

Description

Implements the backend changes requested in Issue #39 to validate course-section completion and prevent duplicate progress entries.

Fixes #39

ECSoC26

This contribution is submitted under ECSoC26.

Problem

The previous course-completion flow manually appended section progress to an array.

That allowed:

• Duplicate progress entries
• Lost updates during concurrent requests
• Invalid section IDs
• Progress for sections outside the selected course
• Inconsistent handling of missing courses and unenrolled users

Implementation

Course validation

The controller now:

• Validates that courseId and sectionId are provided
• Rejects malformed MongoDB course IDs
• Returns 404 when the course does not exist
• Verifies that the requested section belongs to the course

Current section-ID compatibility

The current frontend submits a zero-based section index.

The backend continues to support that format:

0 → first section
1 → second section
2 → third section

The implementation also supports embedded section _id or id values for future compatibility.

Enrollment validation

The authenticated user must have an enrollment record for the requested course.

An unenrolled user receives a controlled 403 response.

Atomic duplicate prevention

Progress is now updated with a conditional MongoDB query and $addToSet.

The filter excludes records where the section is already complete:

{
  _id: enrollment._id,
  "progress.sectionId": {
    $ne: normalizedSectionId,
  },
}

The update uses:

{
  $addToSet: {
    progress: {
      sectionId: normalizedSectionId,
    },
  },
}

This prevents repeated and concurrent requests from creating duplicate progress entries.

Idempotent response

A newly completed section returns:

{
  "success": true,
  "alreadyCompleted": false,
  "message": "Section completed successfully"
}

A repeated request returns:

{
  "success": true,
  "alreadyCompleted": true,
  "message": "Section was already completed"
}

Tests added

The backend tests cover:

• Successful section completion
• Duplicate completion
• Atomic $addToSet usage
• Invalid MongoDB course IDs
• Missing courses
• Sections outside the course
• Unenrolled students
• Existing numeric section-index compatibility

Acceptance criteria verification

• courseId and sectionId are validated
• Course existence is checked
• Section membership is checked
• Student enrollment is checked
• Duplicate progress entries are prevented
• The update is atomic
• Repeated requests return an idempotent success response
• Existing frontend section-index behaviour remains compatible
• Backend tests were added
• No frontend changes are included

Verification commands

Syntax checks

node --check controllers/progressController.js
node --check routers/userRoutes.js
node --check schemas/enrolledCourseModel.js

Test suite

cd backend
npm install
npm test

Relevant code checks

grep -nE "isValidObjectId|courseId|sectionId|Section not found|Course not found" controllers/progressController.js
grep -nE "\\$addToSet|progress\\.sectionId|alreadyCompleted" controllers/progressController.js
grep -nE "completeCourseSection|completemodule|progressController" routers/userRoutes.js
grep -nE "duplicate|invalid|unenrolled|not found|\\$addToSet" tests/progress.test.js

Test evidence

Files changed

backend/controllers/progressController.js
backend/schemas/enrolledCourseModel.js
backend/routers/userRoutes.js
backend/package.json
backend/package-lock.json
backend/tests/progress.test.js
docs/issue-39-progress-validation.md

[udaycodespace]

Description

Implements the backend changes requested in Issue #39 to validate course-section completion and prevent duplicate progress entries.

Fixes #39

ECSoC26

This contribution is submitted under ECSoC26.

Problem

The previous course-completion flow manually appended section progress to an array.

That allowed:

• Duplicate progress entries
• Lost updates during concurrent requests
• Invalid section IDs
• Progress for sections outside the selected course
• Inconsistent handling of missing courses and unenrolled users

Implementation

Course validation

The controller now:

• Validates that courseId and sectionId are provided
• Rejects malformed MongoDB course IDs
• Returns 404 when the course does not exist
• Verifies that the requested section belongs to the course

Current section-ID compatibility

The current frontend submits a zero-based section index.

The backend continues to support that format:

0 → first section
1 → second section
2 → third section

The implementation also supports embedded section _id or id values for future compatibility.

Enrollment validation

The authenticated user must have an enrollment record for the requested course.

An unenrolled user receives a controlled 403 response.

Atomic duplicate prevention

Progress is now updated with a conditional MongoDB query and $addToSet.

The filter excludes records where the section is already complete:

{
  _id: enrollment._id,
  "progress.sectionId": {
    $ne: normalizedSectionId,
  },
}

The update uses:

{
  $addToSet: {
    progress: {
      sectionId: normalizedSectionId,
    },
  },
}

This prevents repeated and concurrent requests from creating duplicate progress entries.

Idempotent response

A newly completed section returns:

{
  "success": true,
  "alreadyCompleted": false,
  "message": "Section completed successfully"
}

A repeated request returns:

{
  "success": true,
  "alreadyCompleted": true,
  "message": "Section was already completed"
}

Tests added

The backend tests cover:

• Successful section completion
• Duplicate completion
• Atomic $addToSet usage
• Invalid MongoDB course IDs
• Missing courses
• Sections outside the course
• Unenrolled students
• Existing numeric section-index compatibility

Acceptance criteria verification

• courseId and sectionId are validated
• Course existence is checked
• Section membership is checked
• Student enrollment is checked
• Duplicate progress entries are prevented
• The update is atomic
• Repeated requests return an idempotent success response
• Existing frontend section-index behaviour remains compatible
• Backend tests were added
• No frontend changes are included

Verification commands

Syntax checks

node --check controllers/progressController.js
node --check routers/userRoutes.js
node --check schemas/enrolledCourseModel.js

Test suite

cd backend
npm install
npm test

Relevant code checks

grep -nE "isValidObjectId|courseId|sectionId|Section not found|Course not found" controllers/progressController.js
grep -nE "\\$addToSet|progress\\.sectionId|alreadyCompleted" controllers/progressController.js
grep -nE "completeCourseSection|completemodule|progressController" routers/userRoutes.js
grep -nE "duplicate|invalid|unenrolled|not found|\\$addToSet" tests/progress.test.js

Test evidence

Files changed

backend/controllers/progressController.js
backend/schemas/enrolledCourseModel.js
backend/routers/userRoutes.js
backend/package.json
backend/package-lock.json
backend/tests/progress.test.js
docs/issue-39-progress-validation.md

LGTM!