# Exam Submission System - Complete Implementation

## Overview
The exam submission system now properly handles the complete flow from exam start to grading, with both automatic grading for objective questions and manual grading queues for subjective questions.

## System Flow

### 1. **Student Starts Exam**
- **Trigger:** `trg_before_exam_attempt_insert` fires AFTER INSERT on `exam_attempts`
- **Action:** Creates placeholder records in `student_answer` table for each question
- **Schema:**
  ```
  exam_attempts (status='in_progress') 
    ↓
  [TRIGGER: trg_before_exam_attempt_insert]
    ↓
  student_answer (status='in_progress')
  ```

### 2. **Student Answers Questions & Saves Progress**
- **API:** `POST /api/exams/attempts.php?action=save`
- **Action:** Saves answers to `student_answers` table with status='saved'
- **ON DUPLICATE KEY UPDATE:** Updates answer content if student changes response
- **Schema:**
  ```
  student_answers (
    exam_id, student_id, attempt_id, question_id,
    answer_content, answer_type, status='saved', is_draft=TRUE
  )
  ```

### 3. **Student Submits Exam**
- **API:** `POST /api/exams/attempts.php?action=submit`
- **Flow:**
  1. Calculate score for auto-graded questions using `calculateExamScore()`
  2. Update `exam_attempts` status to 'completed' with final score
  3. Save all answers to `student_answers` with final content
  4. **TRIGGER:** `trg_after_exam_attempt_submit` fires on status change

### 4. **Trigger Fires - Capture Answers**
- **Trigger:** `trg_after_exam_attempt_submit` fires AFTER UPDATE on `exam_attempts`
- **Condition:** Only when status changes TO 'completed' or 'submitted'
- **Action:** Calls `capture_student_exam_submission()` stored procedure
- **Prevention:** Checks if answers already captured to avoid duplicates

### 5. **Stored Procedure - Process Answers**
- **Procedure:** `capture_student_exam_submission(exam_id, student_id, attempt_id)`
- **For Each Question:**
  - Fetch answer from `student_answers` table
  - Get question type from `questions` table
  - **If MCQ/True-False/Matching/Fill-Blanks:** Status = 'submitted'
  - **If Essay/Short Answer/Code:** Status = 'pending_manual_review'
  - Insert/Update into `student_answer` table

### 6. **Auto-Grading Results**
- **Objective Questions** (MCQ, True-False, Matching):
  - Automatically checked against correct answers
  - `is_correct` and `score` populated in `student_answer`
  - Status: 'submitted'

- **Subjective Questions** (Essay, Short Answer, Code):
  - Answer captured but NOT scored
  - `score` = NULL, `is_correct` = NULL
  - Status: 'pending_manual_review'
  - Ready for instructor grading queue

## Database Tables

### `exam_attempts`
Tracks each student's exam attempt with submission state:
```
id, exam_id, student_id, attempt_number,
status (in_progress→completed), score, max_score, percentage,
started_at, completed_at
```

### `student_answers` 
Stores student responses during the exam (write-optimized):
```
id, exam_id, student_id, attempt_id, question_id,
answer_content, answer_type, status (saved),
is_graded, grading_method, score
```

### `student_answer`
Final submission storage with grading results (read-optimized):
```
answer_id, exam_id, student_id, question_id, attempt_number,
answer_text, answer_choice, is_correct, score,
status (submitted/pending_manual_review), submitted_at
```

## Triggers

### `trg_before_exam_attempt_insert`
```
Event: AFTER INSERT ON exam_attempts
Timing: When student starts exam
Action: INSERT INTO student_answer (placeholders) for all exam questions
```

### `trg_after_exam_attempt_submit`
```
Event: AFTER UPDATE ON exam_attempts
Condition: NEW.status IN ('completed', 'submitted') AND OLD.status != NEW.status
Action: CALL capture_student_exam_submission()
Dedup: Checks if answers already captured
```

## Status Enums

### `student_answer.status`
- `pending` - Initially set (default)
- `in_progress` - Placeholder state
- `submitted` - Auto-graded questions complete
- `pending_manual_review` - Essay/Code awaiting grading
- `graded` - Manually graded by instructor
- `reviewed` - Feedback provided

### `student_answers.status`
- `in_progress` - First save
- `saved` - Draft answer
- `submitted` - Final submission
- `pending_manual_review` - Manual grading needed
- `graded` - Grading complete

## Key Features

✅ **Placeholder Records**
- Created immediately when exam starts
- Ensures all questions have answer records
- Optimizes database structure

✅ **Auto-Grading**
- MCQ Single: Checks if selected option is correct
- MCQ Multiple: Partial credit (correct/total × points)
- True-False: Treated like MCQ single
- Matching: Partial credit for matched pairs
- Fill-Blanks: Case-insensitive exact match

✅ **Manual Grading Queue**
- Essays automatically marked for review
- Short answers marked for review
- Code submissions marked for review
- Clear `pending_manual_review` status

✅ **Data Integrity**
- Duplicate key handling via INSERT...ON DUPLICATE KEY UPDATE
- Transaction safety in procedures
- Proper constraints between tables

✅ **Comprehensive Tracking**
- IP address, browser info, device info
- Time spent calculations
- Submit timestamps
- Grading metadata

## API Integration

### Save Progress
```php
POST /api/exams/attempts.php
{
  "action": "save",
  "exam_id": 2,
  "time_spent": 300,
  "answers": {
    "37": "15",          // MCQ option ID
    "38": ["1", "2"],   // Multiple select IDS
    "39": "Written answer for essay"
  }
}
```

### Submit Exam
```php
POST /api/exams/attempts.php
{
  "action": "submit",
  "exam_id": 2,
  "time_spent": 1800,
  "answers": { /* same structure */ }
}
```

## Testing

Run comprehensive end-to-end tests:
```bash
# Test complete flow
php test_exam_submission_complete.php

# Test procedure directly
php test_procedure_direct.php

# Check database setup
php check_tables.php
```

## Fixes Applied

1. ✅ Created `student_answers` table for live answer capture
2. ✅ Fixed status enum values across tables
3. ✅ Installed triggers for exam start and submission
4. ✅ Created improved stored procedure for answer capture
5. ✅ Added `pending_manual_review` status for manual questions
6. ✅ Fixed status handling in procedures
7. ✅ Removed problematic trigger that blocked updates
8. ✅ Verified complete end-to-end flow

## Next Steps

1. **Instructor Grading Dashboard** - Create interface to:
   - View pending manual submissions
   - Grade essay/code questions
   - Provide feedback
   - Update scores

2. **Grading API** - Add endpoints:
   - `POST /api/grading/grade` - Submit grades and feedback
   - `GET /api/grading/pending` - Get pending submissions
   - `GET /api/grading/submission` - Get specific submission

3. **Student Review** - Allow students to:
   - View graded answers
   - See feedback comments
   - Review explanations

4. **Analytics** - Dashboard showing:
   - Class average scores
   - Question difficulty/discrimination
   - Student performance trends

---

**Status:** ✅ COMPLETE - All major systems implemented and tested
