
<?php
session_start();
require_once '../config/database.php';
require_once '../includes/functions.php';

if (!isset($_SESSION['admin_id'])) {
    redirect('index.php');
}

$success = '';
$error = '';

// Handle result deletion
if (isset($_GET['delete_id'])) {
    $delete_id = sanitize_input($_GET['delete_id']);
    
    try {
        // Get session_id from result
        $stmt = $pdo->prepare("SELECT session_id FROM results WHERE id = ?");
        $stmt->execute([$delete_id]);
        $result = $stmt->fetch(PDO::FETCH_ASSOC);
        
        if ($result) {
            // Delete student answers
            $stmt = $pdo->prepare("DELETE FROM student_answers WHERE session_id = ?");
            $stmt->execute([$result['session_id']]);
            
            // Delete result
            $stmt = $pdo->prepare("DELETE FROM results WHERE id = ?");
            $stmt->execute([$delete_id]);
            
            // Update exam session
            $stmt = $pdo->prepare("UPDATE exam_sessions SET status = 'abandoned' WHERE id = ?");
            $stmt->execute([$result['session_id']]);
            
            $success = "Result deleted successfully!";
        }
    } catch (PDOException $e) {
        $error = "Error deleting result: " . $e->getMessage();
    }
}

// Handle bulk actions
if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['bulk_action'])) {
    $bulk_action = sanitize_input($_POST['bulk_action']);
    $selected_results = $_POST['selected_results'] ?? [];
    
    if (empty($selected_results)) {
        $error = "Please select at least one result to perform bulk action.";
    } else {
        try {
            $placeholders = str_repeat('?,', count($selected_results) - 1) . '?';
            
            if ($bulk_action === 'delete') {
                // Get session IDs for selected results
                $stmt = $pdo->prepare("SELECT session_id FROM results WHERE id IN ($placeholders)");
                $stmt->execute($selected_results);
                $sessions = $stmt->fetchAll(PDO::FETCH_COLUMN);
                
                if ($sessions) {
                    // Delete student answers
                    $session_placeholders = str_repeat('?,', count($sessions) - 1) . '?';
                    $stmt = $pdo->prepare("DELETE FROM student_answers WHERE session_id IN ($session_placeholders)");
                    $stmt->execute($sessions);
                    
                    // Delete results
                    $stmt = $pdo->prepare("DELETE FROM results WHERE id IN ($placeholders)");
                    $stmt->execute($selected_results);
                    
                    // Update exam sessions
                    $stmt = $pdo->prepare("UPDATE exam_sessions SET status = 'abandoned' WHERE id IN ($session_placeholders)");
                    $stmt->execute($sessions);
                    
                    $success = count($selected_results) . " result(s) deleted successfully!";
                }
            } elseif ($bulk_action === 'export') {
                // Export functionality would go here
                $success = "Export functionality for " . count($selected_results) . " result(s) would be implemented here.";
            }
        } catch (PDOException $e) {
            $error = "Error performing bulk action: " . $e->getMessage();
        }
    }
}

// Get filter parameters
$exam_id = $_GET['exam_id'] ?? '';
$student_id = $_GET['student_id'] ?? '';
$date_from = $_GET['date_from'] ?? '';
$date_to = $_GET['date_to'] ?? '';
$min_score = $_GET['min_score'] ?? '';
$max_score = $_GET['max_score'] ?? '';

// Build query for results with filters
$query = "
    SELECT r.*, 
           es.student_id,
           es.exam_id,
           es.start_time,
           es.end_time,
           s.reg_number,
           s.full_name as student_name,
           e.name as exam_name,
           e.year as exam_year
    FROM results r 
    JOIN exam_sessions es ON r.session_id = es.id 
    JOIN students s ON es.student_id = s.id 
    JOIN exams e ON es.exam_id = e.id 
    WHERE 1=1
";

$params = [];

// Apply filters
if ($exam_id) {
    $query .= " AND es.exam_id = ?";
    $params[] = $exam_id;
}

if ($student_id) {
    $query .= " AND es.student_id = ?";
    $params[] = $student_id;
}

if ($date_from) {
    $query .= " AND DATE(r.submitted_at) >= ?";
    $params[] = $date_from;
}

if ($date_to) {
    $query .= " AND DATE(r.submitted_at) <= ?";
    $params[] = $date_to;
}

if ($min_score) {
    $query .= " AND r.percentage >= ?";
    $params[] = $min_score;
}

if ($max_score) {
    $query .= " AND r.percentage <= ?";
    $params[] = $max_score;
}

// Add sorting
$sort = $_GET['sort'] ?? 'submitted_at';
$order = $_GET['order'] ?? 'desc';
$allowed_sorts = ['submitted_at', 'percentage', 'correct_answers', 'student_name', 'exam_name'];
$allowed_orders = ['asc', 'desc'];
$sort = in_array($sort, $allowed_sorts) ? $sort : 'submitted_at';
$order = in_array($order, $allowed_orders) ? $order : 'desc';
$query .= " ORDER BY $sort $order";

$stmt = $pdo->prepare($query);
$stmt->execute($params);
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Get exams for filter dropdown
$stmt = $pdo->prepare("SELECT id, name, year FROM exams ORDER BY year DESC, name");
$stmt->execute();
$exams = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Get students for filter dropdown
$stmt = $pdo->prepare("SELECT id, reg_number, full_name FROM students ORDER BY full_name");
$stmt->execute();
$students = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Calculate statistics
$total_results = count($results);
$average_score = $total_results > 0 ? array_sum(array_column($results, 'percentage')) / $total_results : 0;
$highest_score = $total_results > 0 ? max(array_column($results, 'percentage')) : 0;
$lowest_score = $total_results > 0 ? min(array_column($results, 'percentage')) : 0;

// Score distribution
$score_ranges = [
    '90-100' => 0,
    '80-89' => 0,
    '70-79' => 0,
    '60-69' => 0,
    '50-59' => 0,
    '0-49' => 0
];

foreach ($results as $result) {
    $score = $result['percentage'];
    if ($score >= 90) $score_ranges['90-100']++;
    elseif ($score >= 80) $score_ranges['80-89']++;
    elseif ($score >= 70) $score_ranges['70-79']++;
    elseif ($score >= 60) $score_ranges['60-69']++;
    elseif ($score >= 50) $score_ranges['50-59']++;
    else $score_ranges['0-49']++;
}
?>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>View Results - Admin</title>
    <link rel="stylesheet" href="../assets/css/style.css">
    <script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
    <style>
        .admin-content {
            background: white;
            border-radius: 15px;
            box-shadow: 0 5px 25px rgba(0,0,0,0.1);
            overflow: hidden;
            margin: 2rem 0;
        }

        .content-header {
            background: linear-gradient(135deg, #2c3e50, #34495e);
            color: white;
            padding: 2rem;
        }

        .content-header h1 {
            margin: 0;
            font-size: 2rem;
            font-weight: 700;
        }

        .content-header p {
            margin: 0.5rem 0 0 0;
            opacity: 0.9;
        }

        .content-body {
            padding: 2rem;
        }

        .alert {
            padding: 15px 20px;
            border-radius: 10px;
            margin-bottom: 2rem;
            font-weight: 500;
            border-left: 4px solid;
        }

        .alert-success {
            background: #d4edda;
            color: #155724;
            border-left-color: #28a745;
        }

        .alert-error {
            background: #f8d7da;
            color: #721c24;
            border-left-color: #dc3545;
        }

        /* Statistics Cards */
        .stats-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 1.5rem;
            margin-bottom: 2rem;
        }

        .stat-card {
            background: white;
            padding: 1.5rem;
            border-radius: 10px;
            box-shadow: 0 3px 10px rgba(0,0,0,0.08);
            text-align: center;
            border-left: 4px solid #3498db;
        }

        .stat-card h3 {
            color: #7f8c8d;
            font-size: 0.9rem;
            text-transform: uppercase;
            margin-bottom: 0.5rem;
            letter-spacing: 0.5px;
        }

        .stat-number {
            font-size: 2rem;
            font-weight: bold;
            color: #2c3e50;
            margin-bottom: 0.5rem;
        }

        .stat-description {
            color: #95a5a6;
            font-size: 0.8rem;
        }

        /* Charts Section */
        .charts-section {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 2rem;
            margin-bottom: 2rem;
        }

        .chart-card {
            background: white;
            padding: 1.5rem;
            border-radius: 10px;
            box-shadow: 0 3px 10px rgba(0,0,0,0.08);
        }

        .chart-card h3 {
            color: #2c3e50;
            margin-bottom: 1rem;
            font-size: 1.1rem;
            text-align: center;
        }

        /* Filter Section */
        .filter-section {
            background: #f8f9fa;
            padding: 2rem;
            border-radius: 10px;
            margin-bottom: 2rem;
        }

        .filter-section h3 {
            color: #2c3e50;
            margin-bottom: 1.5rem;
            font-size: 1.3rem;
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .filter-section h3::before {
            content: '🔍';
            font-size: 1.2rem;
        }

        .filter-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 1.5rem;
            margin-bottom: 1.5rem;
        }

        .form-group {
            margin-bottom: 1rem;
        }

        .form-group label {
            display: block;
            margin-bottom: 0.5rem;
            color: #2c3e50;
            font-weight: 600;
            font-size: 0.9rem;
        }

        .form-group input,
        .form-group select {
            width: 100%;
            padding: 10px 15px;
            border: 2px solid #e1e8ed;
            border-radius: 8px;
            font-size: 16px;
            transition: all 0.3s ease;
            background: white;
        }

        .form-group input:focus,
        .form-group select:focus {
            outline: none;
            border-color: #3498db;
            box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.1);
        }

        .filter-actions {
            display: flex;
            gap: 1rem;
            flex-wrap: wrap;
        }

        /* Controls Section */
        .controls-section {
            display: flex;
            justify-content: between;
            align-items: center;
            margin-bottom: 1.5rem;
            flex-wrap: wrap;
            gap: 1rem;
        }

        .results-count {
            color: #2c3e50;
            font-weight: 600;
        }

        .bulk-actions {
            display: flex;
            gap: 0.5rem;
            align-items: center;
        }

        /* Buttons */
        .btn {
            padding: 10px 20px;
            border: none;
            border-radius: 8px;
            font-size: 14px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            text-decoration: none;
            display: inline-flex;
            align-items: center;
            gap: 8px;
        }

        .btn-primary {
            background: #3498db;
            color: white;
        }

        .btn-primary:hover {
            background: #2980b9;
            transform: translateY(-2px);
            box-shadow: 0 5px 15px rgba(52, 152, 219, 0.3);
        }

        .btn-secondary {
            background: #95a5a6;
            color: white;
        }

        .btn-secondary:hover {
            background: #7f8c8d;
            transform: translateY(-2px);
        }

        .btn-success {
            background: #27ae60;
            color: white;
        }

        .btn-success:hover {
            background: #219a52;
            transform: translateY(-2px);
        }

        .btn-danger {
            background: #e74c3c;
            color: white;
        }

        .btn-danger:hover {
            background: #c0392b;
            transform: translateY(-2px);
        }

        .btn-warning {
            background: #f39c12;
            color: white;
        }

        .btn-warning:hover {
            background: #d35400;
            transform: translateY(-2px);
        }

        .btn-info {
            background: #17a2b8;
            color: white;
        }

        .btn-info:hover {
            background: #138496;
            transform: translateY(-2px);
        }

        .btn-sm {
            padding: 6px 12px;
            font-size: 0.8rem;
            border-radius: 6px;
        }

        /* Results Table */
        .results-section h3 {
            color: #2c3e50;
            margin-bottom: 1.5rem;
            font-size: 1.3rem;
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .results-section h3::before {
            content: '📊';
            font-size: 1.2rem;
        }

        .results-table {
            width: 100%;
            background: white;
            border-radius: 10px;
            overflow: hidden;
            box-shadow: 0 3px 10px rgba(0,0,0,0.08);
            margin-bottom: 2rem;
        }

        .results-table table {
            width: 100%;
            border-collapse: collapse;
        }

        .results-table th {
            background: #34495e;
            color: white;
            padding: 15px;
            text-align: left;
            font-weight: 600;
            font-size: 0.9rem;
            text-transform: uppercase;
            letter-spacing: 0.5px;
            cursor: pointer;
            transition: background 0.3s ease;
        }

        .results-table th:hover {
            background: #2c3e50;
        }

        .results-table th.sortable::after {
            content: ' ↕';
            opacity: 0.5;
        }

        .results-table td {
            padding: 15px;
            border-bottom: 1px solid #e1e8ed;
            vertical-align: middle;
        }

        .results-table tr:hover {
            background: #f8f9fa;
        }

        .results-table tr:last-child td {
            border-bottom: none;
        }

        .student-info {
            display: flex;
            align-items: center;
            gap: 12px;
        }

        .student-avatar {
            width: 40px;
            height: 40px;
            border-radius: 50%;
            background: linear-gradient(135deg, #3498db, #2980b9);
            display: flex;
            align-items: center;
            justify-content: center;
            font-weight: bold;
            color: white;
            font-size: 1.2rem;
        }

        .student-details h4 {
            margin: 0;
            color: #2c3e50;
            font-size: 1rem;
        }

        .student-details p {
            margin: 2px 0 0 0;
            color: #7f8c8d;
            font-size: 0.85rem;
        }

        .exam-info h4 {
            margin: 0;
            color: #2c3e50;
            font-size: 1rem;
        }

        .exam-info p {
            margin: 2px 0 0 0;
            color: #7f8c8d;
            font-size: 0.85rem;
        }

        .score-display {
            text-align: center;
        }

        .score-value {
            font-size: 1.5rem;
            font-weight: bold;
            margin-bottom: 5px;
        }

        .score-percentage {
            font-size: 0.9rem;
            color: #7f8c8d;
        }

        .score-excellent { color: #27ae60; }
        .score-good { color: #3498db; }
        .score-average { color: #f39c12; }
        .score-poor { color: #e74c3c; }

        .performance-badge {
            padding: 4px 8px;
            border-radius: 12px;
            font-size: 0.75rem;
            font-weight: 600;
            text-transform: uppercase;
        }

        .badge-excellent { background: #d4edda; color: #155724; }
        .badge-good { background: #d1ecf1; color: #0c5460; }
        .badge-average { background: #fff3cd; color: #856404; }
        .badge-poor { background: #f8d7da; color: #721c24; }

        .duration {
            text-align: center;
            color: #7f8c8d;
            font-size: 0.9rem;
        }

        .action-buttons {
            display: flex;
            gap: 0.5rem;
            flex-wrap: wrap;
        }

        .no-results {
            text-align: center;
            padding: 3rem;
            color: #7f8c8d;
            background: #f8f9fa;
            border-radius: 10px;
        }

        .no-results .icon {
            font-size: 3rem;
            margin-bottom: 1rem;
            opacity: 0.5;
        }

        /* Checkbox */
        .result-checkbox {
            width: 18px;
            height: 18px;
            cursor: pointer;
        }

        /* Modal */
        .modal {
            display: none;
            position: fixed;
            z-index: 1000;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.5);
            backdrop-filter: blur(5px);
        }

        .modal-content {
            background: white;
            margin: 5% auto;
            padding: 2rem;
            border-radius: 15px;
            width: 90%;
            max-width: 500px;
            position: relative;
            animation: modalSlideIn 0.3s ease;
        }

        @keyframes modalSlideIn {
            from {
                opacity: 0;
                transform: translateY(-50px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        .modal-header {
            display: flex;
            justify-content: between;
            align-items: center;
            margin-bottom: 1.5rem;
        }

        .modal-header h3 {
            margin: 0;
            color: #2c3e50;
        }

        .close-modal {
            background: none;
            border: none;
            font-size: 1.5rem;
            cursor: pointer;
            color: #7f8c8d;
            padding: 0;
            width: 30px;
            height: 30px;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 50%;
        }

        .close-modal:hover {
            background: #f8f9fa;
            color: #e74c3c;
        }

        /* Responsive Design */
        @media (max-width: 1024px) {
            .charts-section {
                grid-template-columns: 1fr;
            }
        }

        @media (max-width: 768px) {
            .content-body {
                padding: 1.5rem;
            }

            .filter-grid {
                grid-template-columns: 1fr;
            }

            .controls-section {
                flex-direction: column;
                align-items: stretch;
            }

            .bulk-actions {
                justify-content: space-between;
            }

            .results-table {
                overflow-x: auto;
            }

            .results-table table {
                min-width: 1000px;
            }

            .action-buttons {
                flex-direction: column;
            }

            .btn-sm {
                text-align: center;
                justify-content: center;
            }

            .modal-content {
                margin: 10% auto;
                width: 95%;
                padding: 1.5rem;
            }
        }

        @media (max-width: 480px) {
            .content-header {
                padding: 1.5rem;
            }

            .content-header h1 {
                font-size: 1.5rem;
            }

            .filter-section {
                padding: 1.5rem;
            }

            .stats-grid {
                grid-template-columns: 1fr;
            }
        }
    </style>
</head>
<body>
    <?php include '../includes/header.php'; ?>
    
    <div class="container">
        <div class="admin-content">
            <div class="content-header">
                <h1>Exam Results Analysis</h1>
                <p>Comprehensive overview of student performance and exam results</p>
            </div>

            <div class="content-body">
                <?php if (!empty($success)): ?>
                    <div class="alert alert-success"><?php echo $success; ?></div>
                <?php endif; ?>

                <?php if (!empty($error)): ?>
                    <div class="alert alert-error"><?php echo $error; ?></div>
                <?php endif; ?>

                <!-- Statistics -->
                <div class="stats-grid">
                    <div class="stat-card">
                        <div class="stat-number"><?php echo $total_results; ?></div>
                        <h3>Total Results</h3>
                        <p class="stat-description">Exam attempts completed</p>
                    </div>
                    <div class="stat-card">
                        <div class="stat-number"><?php echo number_format($average_score, 1); ?>%</div>
                        <h3>Average Score</h3>
                        <p class="stat-description">Across all attempts</p>
                    </div>
                    <div class="stat-card">
                        <div class="stat-number"><?php echo number_format($highest_score, 1); ?>%</div>
                        <h3>Highest Score</h3>
                        <p class="stat-description">Best performance</p>
                    </div>
                    <div class="stat-card">
                        <div class="stat-number"><?php echo number_format($lowest_score, 1); ?>%</div>
                        <h3>Lowest Score</h3>
                        <p class="stat-description">Worst performance</p>
                    </div>
                </div>

                <!-- Charts Section -->
                <div class="charts-section">
                    <div class="chart-card">
                        <h3>Score Distribution</h3>
                        <canvas id="scoreDistributionChart" height="250"></canvas>
                    </div>
                    <div class="chart-card">
                        <h3>Performance Overview</h3>
                        <canvas id="performanceChart" height="250"></canvas>
                    </div>
                </div>

                <!-- Filter Section -->
                <div class="filter-section">
                    <h3>Filter Results</h3>
                    <form method="GET" action="">
                        <div class="filter-grid">
                            <div class="form-group">
                                <label for="exam_id">Exam</label>
                                <select id="exam_id" name="exam_id">
                                    <option value="">All Exams</option>
                                    <?php foreach ($exams as $exam): ?>
                                        <option value="<?php echo $exam['id']; ?>" 
                                            <?php echo $exam_id == $exam['id'] ? 'selected' : ''; ?>>
                                            <?php echo htmlspecialchars($exam['name']); ?> (<?php echo $exam['year']; ?>)
                                        </option>
                                    <?php endforeach; ?>
                                </select>
                            </div>

                            <div class="form-group">
                                <label for="student_id">Student</label>
                                <select id="student_id" name="student_id">
                                    <option value="">All Students</option>
                                    <?php foreach ($students as $student): ?>
                                        <option value="<?php echo $student['id']; ?>" 
                                            <?php echo $student_id == $student['id'] ? 'selected' : ''; ?>>
                                            <?php echo htmlspecialchars($student['full_name']); ?> (<?php echo htmlspecialchars($student['reg_number']); ?>)
                                        </option>
                                    <?php endforeach; ?>
                                </select>
                            </div>

                            <div class="form-group">
                                <label for="date_from">Date From</label>
                                <input type="date" id="date_from" name="date_from" value="<?php echo htmlspecialchars($date_from); ?>">
                            </div>

                            <div class="form-group">
                                <label for="date_to">Date To</label>
                                <input type="date" id="date_to" name="date_to" value="<?php echo htmlspecialchars($date_to); ?>">
                            </div>

                            <div class="form-group">
                                <label for="min_score">Minimum Score (%)</label>
                                <input type="number" id="min_score" name="min_score" min="0" max="100" 
                                       value="<?php echo htmlspecialchars($min_score); ?>" placeholder="0">
                            </div>

                            <div class="form-group">
                                <label for="max_score">Maximum Score (%)</label>
                                <input type="number" id="max_score" name="max_score" min="0" max="100" 
                                       value="<?php echo htmlspecialchars($max_score); ?>" placeholder="100">
                            </div>
                        </div>

                        <div class="filter-actions">
                            <button type="submit" class="btn btn-primary">🔍 Apply Filters</button>
                            <a href="view_results.php" class="btn btn-secondary">❌ Clear Filters</a>
                            <button type="button" onclick="exportResults()" class="btn btn-success">📤 Export Results</button>
                        </div>
                    </form>
                </div>

                <!-- Results List -->
                <div class="results-section">
                    <div class="controls-section">
                        <div class="results-count">
                            Showing <?php echo $total_results; ?> result(s)
                            <?php if ($exam_id || $student_id || $date_from || $date_to || $min_score || $max_score): ?>
                                (filtered)
                            <?php endif; ?>
                        </div>

                        <form method="POST" class="bulk-actions">
                            <select name="bulk_action" class="btn btn-secondary" style="padding: 8px 15px;">
                                <option value="">Bulk Actions</option>
                                <option value="export">📤 Export Selected</option>
                                <option value="delete">🗑️ Delete Selected</option>
                            </select>
                            <button type="submit" class="btn btn-warning">Apply</button>
                        </form>
                    </div>

                    <h3>Exam Results</h3>

                    <?php if (count($results) > 0): ?>
                        <form method="POST" id="bulkForm">
                            <div class="results-table">
                                <table>
                                    <thead>
                                        <tr>
                                            <th width="30">
                                                <input type="checkbox" id="selectAll" class="result-checkbox">
                                            </th>
                                            <th class="sortable" onclick="sortTable('student_name')">Student</th>
                                            <th class="sortable" onclick="sortTable('exam_name')">Exam</th>
                                            <th class="sortable" onclick="sortTable('correct_answers')">Score</th>
                                            <th class="sortable" onclick="sortTable('percentage')">Percentage</th>
                                            <th>Performance</th>
                                            <th class="sortable" onclick="sortTable('submitted_at')">Submitted</th>
                                            <th>Duration</th>
                                            <th>Actions</th>
                                        </tr>
                                    </thead>
                                    <tbody>
                                        <?php foreach ($results as $result): 
                                            $score_class = '';
                                            $performance_badge = '';
                                            if ($result['percentage'] >= 80) {
                                                $score_class = 'score-excellent';
                                                $performance_badge = 'badge-excellent';
                                                $performance_text = 'Excellent';
                                            } elseif ($result['percentage'] >= 60) {
                                                $score_class = 'score-good';
                                                $performance_badge = 'badge-good';
                                                $performance_text = 'Good';
                                            } elseif ($result['percentage'] >= 40) {
                                                $score_class = 'score-average';
                                                $performance_badge = 'badge-average';
                                                $performance_text = 'Average';
                                            } else {
                                                $score_class = 'score-poor';
                                                $performance_badge = 'badge-poor';
                                                $performance_text = 'Poor';
                                            }

                                            $start_time = new DateTime($result['start_time']);
                                            $end_time = new DateTime($result['end_time']);
                                            $duration = $start_time->diff($end_time);
                                            $duration_display = $duration->h > 0 ? 
                                                sprintf('%dh %dm', $duration->h, $duration->i) : 
                                                sprintf('%dm %ds', $duration->i, $duration->s);
                                        ?>
                                            <tr>
                                                <td>
                            <input type="checkbox" name="selected_results[]" value="<?php echo $result['id']; ?>" class="result-checkbox">
                                                </td>
                                                <td>
                                                    <div class="student-info">
                                                        <div class="student-avatar">
                                                            <?php echo strtoupper(substr($result['student_name'], 0, 1)); ?>
                                                        </div>
                                                        <div class="student-details">
                                                            <h4><?php echo htmlspecialchars($result['student_name']); ?></h4>
                                                            <p><?php echo htmlspecialchars($result['reg_number']); ?></p>
                                                        </div>
                                                    </div>
                                                </td>
                                                <td>
                                                    <div class="exam-info">
                                                        <h4><?php echo htmlspecialchars($result['exam_name']); ?></h4>
                                                        <p><?php echo $result['exam_year']; ?></p>
                                                    </div>
                                                </td>
                                                <td class="score-display">
                                                    <div class="score-value <?php echo $score_class; ?>">
                                                        <?php echo $result['correct_answers']; ?>/<?php echo $result['total_questions']; ?>
                                                    </div>
                                                    <div class="score-percentage">
                                                        <?php echo $result['questions_attempted']; ?> attempted
                                                    </div>
                                                </td>
                                                <td class="score-display">
                                                    <div class="score-value <?php echo $score_class; ?>">
                                                        <?php echo number_format($result['percentage'], 1); ?>%
                                                    </div>
                                                </td>
                                                <td>
                                                    <span class="performance-badge <?php echo $performance_badge; ?>">
                                                        <?php echo $performance_text; ?>
                                                    </span>
                                                </td>
                                                <td>
                                                    <?php echo date('M j, Y g:i A', strtotime($result['submitted_at'])); ?>
                                                </td>
                                                <td class="duration">
                                                    <?php echo $duration_display; ?>
                                                </td>
                                                <td>
                                      <div class="action-buttons">
                                        <a href="view_result_details.php?result_id=<?php echo $result['id']; ?>" class="btn btn-info btn-sm">
                                                            👁️ Details
                                                        </a>
                                                        
                                       <a href="vd.php?result_id=<?php echo $result['id']; ?>" class="btn btn-info btn-sm">
                                                            👁 View️ Details 2
                                                        </a>
                                                        
                                                        
                                                        <button onclick="confirmDelete(<?php echo $result['id']; ?>, '<?php echo htmlspecialchars($result['student_name']); ?>')" 
                                                                class="btn btn-danger btn-sm">
                                                            🗑️ Delete
                                                        </button>
                                                    </div>
                                                </td>
                                            </tr>
                                        <?php endforeach; ?>
                                    </tbody>
                                </table>
                            </div>
                        </form>
                    <?php else: ?>
                        <div class="no-results">
                            <div class="icon">📊</div>
                            <h3>No Results Found</h3>
                            <p><?php echo ($exam_id || $student_id || $date_from || $date_to || $min_score || $max_score) ? 
                                'No results match your filter criteria. Try adjusting your filters.' : 
                                'No exam results have been recorded yet.'; ?></p>
                            <?php if ($exam_id || $student_id || $date_from || $date_to || $min_score || $max_score): ?>
                                <a href="view_results.php" class="btn btn-primary">View All Results</a>
                            <?php endif; ?>
                        </div>
                    <?php endif; ?>
                </div>
            </div>
        </div>
    </div>

    <!-- Delete Confirmation Modal -->
    <div id="deleteModal" class="modal">
        <div class="modal-content">
            <div class="modal-header">
                <h3>Confirm Deletion</h3>
                <button class="close-modal" onclick="closeModal()">×</button>
            </div>
            <p id="deleteMessage">Are you sure you want to delete this result? This action cannot be undone.</p>
            <div class="form-actions">
                <button id="confirmDelete" class="btn btn-danger">🗑️ Delete Result</button>
                <button onclick="closeModal()" class="btn btn-secondary">❌ Cancel</button>
            </div>
        </div>
    </div>
<br/>
<?php include '../includes/footer.php'; ?> 
    <script>
        // Charts
        const scoreDistributionChart = new Chart(
            document.getElementById('scoreDistributionChart'),
            {
                type: 'bar',
                data: {
                    labels: ['90-100%', '80-89%', '70-79%', '60-69%', '50-59%', '0-49%'],
                    datasets: [{
                        label: 'Number of Students',
                        data: [
                            <?php echo $score_ranges['90-100']; ?>,
                            <?php echo $score_ranges['80-89']; ?>,
                            <?php echo $score_ranges['70-79']; ?>,
                            <?php echo $score_ranges['60-69']; ?>,
                            <?php echo $score_ranges['50-59']; ?>,
                            <?php echo $score_ranges['0-49']; ?>
                        ],
                        backgroundColor: [
                            '#27ae60', '#2ecc71', '#3498db', '#f39c12', '#e67e22', '#e74c3c'
                        ],
                        borderWidth: 0
                    }]
                },
                options: {
                    responsive: true,
                    plugins: {
                        legend: {
                            display: false
                        }
                    },
                    scales: {
                        y: {
                            beginAtZero: true,
                            ticks: {
                                stepSize: 1
                            }
                        }
                    }
                }
            }
        );

        const performanceChart = new Chart(
            document.getElementById('performanceChart'),
            {
                type: 'doughnut',
                data: {
                    labels: ['Excellent (80-100%)', 'Good (60-79%)', 'Average (40-59%)', 'Poor (0-39%)'],
                    datasets: [{
                        data: [
                            <?php echo $score_ranges['90-100'] + $score_ranges['80-89']; ?>,
                            <?php echo $score_ranges['70-79'] + $score_ranges['60-69']; ?>,
                            <?php echo $score_ranges['50-59']; ?>,
                            <?php echo $score_ranges['0-49']; ?>
                        ],
                        backgroundColor: [
                            '#27ae60', '#3498db', '#f39c12', '#e74c3c'
                        ],
                        borderWidth: 0
                    }]
                },
                options: {
                    responsive: true,
                    plugins: {
                        legend: {
                            position: 'bottom'
                        }
                    }
                }
            }
        );

        let resultToDelete = null;

        // Select All functionality
        document.getElementById('selectAll')?.addEventListener('change', function() {
            const checkboxes = document.querySelectorAll('input[name="selected_results[]"]');
            checkboxes.forEach(checkbox => {
                checkbox.checked = this.checked;
            });
        });

        function sortTable(column) {
            const url = new URL(window.location.href);
            const currentSort = url.searchParams.get('sort');
            const currentOrder = url.searchParams.get('order');
            
            let newOrder = 'desc';
            if (currentSort === column && currentOrder === 'desc') {
                newOrder = 'asc';
            }
            
            url.searchParams.set('sort', column);
            url.searchParams.set('order', newOrder);
            window.location.href = url.toString();
        }

        function confirmDelete(resultId, studentName) {
            resultToDelete = resultId;
            document.getElementById('deleteMessage').innerHTML = 
                `Are you sure you want to delete the result for "<strong>${studentName}</strong>"? This action cannot be undone.`;
            document.getElementById('deleteModal').style.display = 'block';
        }

        function closeModal() {
            document.getElementById('deleteModal').style.display = 'none';
            resultToDelete = null;
        }

        document.getElementById('confirmDelete').addEventListener('click', function() {
            if (resultToDelete) {
                window.location.href = 'view_results.php?delete_id=' + resultToDelete;
            }
        });

        function exportResults() {
            // Get current filter parameters
            const params = new URLSearchParams(window.location.search);
            alert('Export functionality would be implemented here with parameters: ' + params.toString());
            // In a real implementation, this would redirect to an export script
            // window.location.href = 'export_results.php?' + params.toString();
        }

        // Close modal when clicking outside
        window.addEventListener('click', function(event) {
            const modal = document.getElementById('deleteModal');
            if (event.target === modal) {
                closeModal();
            }
        });

        // Close modal with Escape key
        document.addEventListener('keydown', function(event) {
            if (event.key === 'Escape') {
                closeModal();
            }
        });

        // Auto-hide alerts after 5 seconds
        setTimeout(function() {
            const alerts = document.querySelectorAll('.alert');
            alerts.forEach(alert => {
                alert.style.opacity = '0';
                alert.style.transition = 'opacity 0.5s ease';
                setTimeout(() => alert.remove(), 500);
            });
        }, 5000);

        // Bulk form submission
        document.querySelector('form[class="bulk-actions"]')?.addEventListener('submit', function(e) {
            const bulkAction = this.querySelector('select[name="bulk_action"]').value;
            const selectedResults = document.querySelectorAll('input[name="selected_results[]"]:checked');
            
            if (selectedResults.length === 0) {
                e.preventDefault();
                alert('Please select at least one result to perform bulk action.');
                return;
            }

            if (bulkAction === 'delete') {
                if (!confirm(`Are you sure you want to delete ${selectedResults.length} result(s)? This action cannot be undone.`)) {
                    e.preventDefault();
                }
            }
        });
    </script>
</body>
</html>