<?php
session_start();
require_once '../config/database.php';
require_once '../includes/functions.php';

if (!isset($_SESSION['student_id'])) {
    redirect('login.php');
}

$exam_id = $_GET['exam_id'] ?? null;
if (!$exam_id) {
    redirect('dashboard.php');
}

// Get exam details
$exam = get_exam_details($exam_id, $pdo);
if (!$exam) {
    die("Exam not found!");
}

// Check if student has an active session
$stmt = $pdo->prepare("SELECT * FROM exam_sessions WHERE student_id = ? AND exam_id = ? AND status = 'in_progress'");
$stmt->execute([$_SESSION['student_id'], $exam_id]);
$session = $stmt->fetch(PDO::FETCH_ASSOC);

if (!$session) {
    // Create new session
    $start_time = date('Y-m-d H:i:s');
    $end_time = date('Y-m-d H:i:s', strtotime("+{$exam['duration']} minutes"));
    $time_remaining = $exam['duration'] * 60;
    
    $stmt = $pdo->prepare("INSERT INTO exam_sessions (student_id, exam_id, start_time, end_time, time_remaining) VALUES (?, ?, ?, ?, ?)");
    $stmt->execute([$_SESSION['student_id'], $exam_id, $start_time, $end_time, $time_remaining]);
    $session_id = $pdo->lastInsertId();
} else {
    $session_id = $session['id'];
    $time_remaining = $session['time_remaining'];
}

// Get questions for this exam
$stmt = $pdo->prepare("SELECT * FROM questions WHERE exam_id = ? ORDER BY id");
$stmt->execute([$exam_id]);
$questions = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Handle question navigation
$current_page = $_GET['page'] ?? 1;
$questions_per_page = 5;
$total_questions = count($questions);
$total_pages = ceil($total_questions / $questions_per_page);

// Calculate question range for current page
$start_index = ($current_page - 1) * $questions_per_page;
$end_index = min($start_index + $questions_per_page, $total_questions) - 1;

// Handle answer submission
if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['submit_answers'])) {
    foreach ($_POST['answers'] as $question_id => $selected_answer) {
        // Check if answer already exists
        $stmt = $pdo->prepare("SELECT id FROM student_answers WHERE session_id = ? AND question_id = ?");
        $stmt->execute([$session_id, $question_id]);
        
        if ($stmt->rowCount() > 0) {
            // Update existing answer
            $stmt = $pdo->prepare("UPDATE student_answers SET selected_answer = ?, is_correct = (SELECT correct_answer = ? FROM questions WHERE id = ?) WHERE session_id = ? AND question_id = ?");
            $stmt->execute([$selected_answer, $selected_answer, $question_id, $session_id, $question_id]);
        } else {
            // Insert new answer
            $stmt = $pdo->prepare("INSERT INTO student_answers (session_id, question_id, selected_answer, is_correct) VALUES (?, ?, ?, (SELECT correct_answer = ? FROM questions WHERE id = ?))");
            $stmt->execute([$session_id, $question_id, $selected_answer, $selected_answer, $question_id]);
        }
    }
    
    // Update time remaining
    $time_remaining = $_POST['time_remaining'];
    $stmt = $pdo->prepare("UPDATE exam_sessions SET time_remaining = ? WHERE id = ?");
    $stmt->execute([$time_remaining, $session_id]);
    
    // Redirect to next page or results
    if ($current_page < $total_pages) {
        redirect("exam.php?exam_id=$exam_id&page=" . ($current_page + 1));
    } else {
        // Submit exam
        $stmt = $pdo->prepare("UPDATE exam_sessions SET status = 'completed', time_remaining = 0 WHERE id = ?");
        $stmt->execute([$session_id]);
        
        // Calculate and save result
        $correct_answers = calculate_score($session_id, $pdo);
        $percentage = ($correct_answers / $total_questions) * 100;
        
        $stmt = $pdo->prepare("INSERT INTO results (session_id, total_questions, questions_attempted, correct_answers, score, percentage) VALUES (?, ?, ?, ?, ?, ?)");
        $stmt->execute([$session_id, $total_questions, $total_questions, $correct_answers, $correct_answers, $percentage]);
        
        redirect("result.php?session_id=$session_id");
    }
}
?>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Exam - <?php echo $exam['name']; ?></title>
    <link rel="stylesheet" href="../assets/css/style.css">
</head>
<body>
    <div class="exam-container">
        <header class="exam-header">
            <div class="exam-info">
                <h2><?php echo $exam['name']; ?> (<?php echo $exam['year']; ?>)</h2>
                <p>Subject: <?php echo $exam['subject_name']; ?></p>
            </div>
            <div class="exam-timer">
                <div id="timer">Time Remaining: <span id="time-display"><?php echo gmdate("H:i:s", $time_remaining); ?></span></div>
            </div>
        </header>
        
        <br/>

        <div class="exam-content" style="width:70%; margin-left:auto; margin-right:auto;">
            <form method="POST" id="exam-form">
                <input type="hidden" name="time_remaining" id="time_remaining" value="<?php echo $time_remaining; ?>">
                
                <div class="questions-section">
                    <?php for ($i = $start_index; $i <= $end_index; $i++): 
                        $question = $questions[$i];
                        $question_num = $i + 1;
                    ?>
                    <div class="question-card">
                        <div class="question-header">
                            <h3>Question <?php echo $question_num; ?></h3>
                            <span class="marks">(<?php echo $question['marks']; ?> mark<?php echo $question['marks'] > 1 ? 's' : ''; ?>)</span>
                        </div>
                        <p class="question-text"><?php echo $question['question_text']; ?></p>
                        
                        <div class="options">
                            <label class="option">
                                <input type="radio" name="answers[<?php echo $question['id']; ?>]" value="A">
                                <span>A. <?php echo $question['option_a']; ?></span>
                            </label>
                            <label class="option">
                                <input type="radio" name="answers[<?php echo $question['id']; ?>]" value="B">
                                <span>B. <?php echo $question['option_b']; ?></span>
                            </label>
                            <label class="option">
                                <input type="radio" name="answers[<?php echo $question['id']; ?>]" value="C">
                                <span>C. <?php echo $question['option_c']; ?></span>
                            </label>
                            <label class="option">
                                <input type="radio" name="answers[<?php echo $question['id']; ?>]" value="D">
                                <span>D. <?php echo $question['option_d']; ?></span>
                            </label>
                        </div>
                    </div>
                    <?php endfor; ?>
                </div>

                <div class="exam-navigation">
                    <div class="pagination">
                        <?php for ($page = 1; $page <= $total_pages; $page++): ?>
                            <a href="exam.php?exam_id=<?php echo $exam_id; ?>&page=<?php echo $page; ?>" class="page-link <?php echo $page == $current_page ? 'active' : ''; ?>">
                                <?php echo $page; ?>
                            </a>
                        <?php endfor; ?>
                    </div>
                    
                    <div class="action-buttons">
                        <?php if ($current_page < $total_pages): ?>
                            <button type="submit" name="submit_answers" class="btn btn-primary">Save & Next</button>
                        <?php else: ?>
                            <button type="submit" name="submit_answers" class="btn btn-success" onclick="return confirm('Are you sure you want to submit the exam?')">Submit Exam</button>
                        <?php endif; ?>
                    </div>
                </div>
            </form>
        </div>
    </div>

    <script>
        // Timer functionality
        let timeRemaining = <?php echo $time_remaining; ?>;
        const timerElement = document.getElementById('time-display');
        const timeInput = document.getElementById('time_remaining');

        function updateTimer() {
            if (timeRemaining <= 0) {
                document.getElementById('exam-form').submit();
                return;
            }

            timeRemaining--;
            timeInput.value = timeRemaining;
            
            const hours = Math.floor(timeRemaining / 3600);
            const minutes = Math.floor((timeRemaining % 3600) / 60);
            const seconds = timeRemaining % 60;
            
            timerElement.textContent = `${hours.toString().padStart(2, '0')}:${minutes.toString().padStart(2, '0')}:${seconds.toString().padStart(2, '0')}`;
        }

        setInterval(updateTimer, 1000);
    </script>
</body>
</html>