<?php
// Start session
session_start();

// Include database configuration
require_once '../../config/database.php';

// Check if user is logged in and has student role
if (!isset($_SESSION['user_id']) || $_SESSION['role'] !== 'student') {
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'message' => 'Unauthorized access']);
    exit;
}

$user_id = $_SESSION['user_id'];

// Check if this is a POST request
if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'message' => 'Invalid request method']);
    exit;
}

// Get POST data
$student_exam_id = isset($_POST['student_exam_id']) ? intval($_POST['student_exam_id']) : 0;
$question_id = isset($_POST['question_id']) ? intval($_POST['question_id']) : 0;
$answer_type = isset($_POST['answer_type']) ? $_POST['answer_type'] : '';
$answer_value = isset($_POST['answer_value']) ? $_POST['answer_value'] : '';

// Validate required parameters
if (empty($student_exam_id) || empty($question_id) || empty($answer_type)) {
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'message' => 'Missing required parameters']);
    exit;
}

// Verify the student exam belongs to the current user
$verify_query = "SELECT se.*, es.id as exam_id 
                FROM student_exams se
                JOIN exam_schedules es ON se.exam_id = es.id
                WHERE se.id = ? AND se.user_id = ?";
$stmt = $conn->prepare($verify_query);
$stmt->bind_param("ii", $student_exam_id, $user_id);
$stmt->execute();
$verify_result = $stmt->get_result();

if ($verify_result->num_rows === 0) {
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'message' => 'Invalid exam session']);
    exit;
}

$student_exam = $verify_result->fetch_assoc();

// Check if the exam is in progress
if ($student_exam['status'] !== 'in_progress') {
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'message' => 'Exam is not in progress']);
    exit;
}

// Verify the question belongs to this exam
$question_query = "SELECT q.*, eqm.id as map_id 
                  FROM questions q
                  JOIN exam_question_maps eqm ON q.id = eqm.question_id
                  WHERE q.id = ? AND eqm.exam_id = ?";
$stmt = $conn->prepare($question_query);
$stmt->bind_param("ii", $question_id, $student_exam['exam_id']);
$stmt->execute();
$question_result = $stmt->get_result();

if ($question_result->num_rows === 0) {
    header('Content-Type: application/json');
    echo json_encode(['success' => false, 'message' => 'Question not found in this exam']);
    exit;
}

$question = $question_result->fetch_assoc();

// Prepare variables for answer
$selected_option_id = null;
$answer_text = null;
$is_correct = null;
$marks_obtained = null;

// Process based on answer type
if ($answer_type === 'option' && !empty($answer_value)) {
    // For multiple choice or true/false questions
    $selected_option_id = intval($answer_value);
    
    // Check if this option is correct
    $option_query = "SELECT * FROM question_options 
                   WHERE id = ? AND question_id = ?";
    $stmt = $conn->prepare($option_query);
    $stmt->bind_param("ii", $selected_option_id, $question_id);
    $stmt->execute();
    $option_result = $stmt->get_result();
    
    if ($option_result->num_rows > 0) {
        $option = $option_result->fetch_assoc();
        $is_correct = $option['is_correct'] ? 1 : 0;
        $marks_obtained = $is_correct ? $question['marks'] : 0;
    } else {
        // Invalid option ID
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'message' => 'Invalid option selected']);
        exit;
    }
} elseif ($answer_type === 'text') {
    // For short answer or essay questions
    $answer_text = trim($answer_value);
    // These will be manually graded later
    $is_correct = null;
    $marks_obtained = null;
}

// Check if an answer already exists for this question
$existing_answer_query = "SELECT id FROM student_answers 
                         WHERE student_exam_id = ? AND question_id = ?";
$stmt = $conn->prepare($existing_answer_query);
$stmt->bind_param("ii", $student_exam_id, $question_id);
$stmt->execute();
$existing_result = $stmt->get_result();

if ($existing_result->num_rows > 0) {
    // Update existing answer
    $existing_answer = $existing_result->fetch_assoc();
    $answer_id = $existing_answer['id'];
    
    $update_query = "UPDATE student_answers 
                   SET answer_text = ?, selected_option_id = ?, is_correct = ?, marks_obtained = ?, 
                       updated_at = CURRENT_TIMESTAMP
                   WHERE id = ?";
    $stmt = $conn->prepare($update_query);
    $stmt->bind_param("siidi", $answer_text, $selected_option_id, $is_correct, $marks_obtained, $answer_id);
    
    if (!$stmt->execute()) {
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'message' => 'Failed to update answer: ' . $stmt->error]);
        exit;
    }
} else {
    // Insert new answer
    $insert_query = "INSERT INTO student_answers 
                    (student_exam_id, question_id, answer_text, selected_option_id, is_correct, marks_obtained) 
                    VALUES (?, ?, ?, ?, ?, ?)";
    $stmt = $conn->prepare($insert_query);
    $stmt->bind_param("iisiid", $student_exam_id, $question_id, $answer_text, $selected_option_id, $is_correct, $marks_obtained);
    
    if (!$stmt->execute()) {
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'message' => 'Failed to save answer: ' . $stmt->error]);
        exit;
    }
}

// Return success response
header('Content-Type: application/json');
echo json_encode([
    'success' => true, 
    'message' => 'Answer saved successfully',
    'question_id' => $question_id,
    'is_correct' => $is_correct,
    'marks_obtained' => $marks_obtained
]);
exit;