<?php
// Include header
include_once 'includes/header.php';

// Check if instructor is logged in
if (!isset($_SESSION['user_id']) || $_SESSION['role'] !== 'instructor') {
    header('Location: ../login.php');
    exit;
}

// Check if attendance table exists and create it if not
function check_attendance_table_exists($conn) {
    $check_table_sql = "SHOW TABLES LIKE 'attendance'";
    $result = $conn->query($check_table_sql);
    
    if ($result->num_rows == 0) {
        // Table doesn't exist, include the setup script
        include_once '../admin/database/setup_attendance_table.php';
        return false;
    }
    return true;
}

// Check and create attendance table if needed
$attendance_table_exists = check_attendance_table_exists($conn);

$instructor_id = $_SESSION['user_id'];
$success_message = '';
$error_message = '';
$selected_date = date('Y-m-d');

// Handle form submission for attendance
if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['submit_attendance'])) {
    $date = $_POST['attendance_date'];
    $attendance_data = $_POST['attendance'] ?? [];

    if (empty($date)) {
        $error_message = "Please select a date.";
    } else {
        // Begin transaction
        $conn->begin_transaction();
        
        try {
            // First, delete any existing attendance records for this date marked by this instructor
            $delete_stmt = $conn->prepare("DELETE FROM attendance WHERE date = ? AND marked_by = ?");
            $delete_stmt->bind_param("si", $date, $instructor_id);
            $delete_stmt->execute();
            
            // Then insert new attendance records
            if (!empty($attendance_data)) {
                $insert_stmt = $conn->prepare("INSERT INTO attendance (enrollment_id, course_id, student_id, date, status, marked_by, notes) VALUES (?, ?, ?, ?, ?, ?, ?)");
                
                foreach ($attendance_data as $enrollment_id => $data) {
                    $student_id = $data['id'];
                    $course_id = $data['course_id'];
                    $status = $data['status'];
                    $notes = $data['notes'] ?? '';
                    
                    $insert_stmt->bind_param("iiissss", $enrollment_id, $course_id, $student_id, $date, $status, $instructor_id, $notes);
                    $insert_stmt->execute();
                }
                
                $insert_stmt->close();
            }
            
            // Commit transaction
            $conn->commit();
            $success_message = "Attendance successfully recorded for " . date('F d, Y', strtotime($date));
            $selected_date = $date;
            
        } catch (Exception $e) {
            // Rollback transaction on error
            $conn->rollback();
            $error_message = "Error recording attendance: " . $e->getMessage();
        }
    }
}

// If date is selected from get parameter
if (isset($_GET['date'])) {
    $selected_date = $_GET['date'];
}

// Get all enrolled students (not course-specific)
$students_query = "
SELECT 
    u.id,
    u.username,
    u.first_name,
    u.last_name,
    u.email,
    u.profile_image,
    e.id AS enrollment_id,
    e.course_id,
    c.title AS course_title,
    e.enrollment_date,
    e.status,
    a.status AS attendance_status,
    a.notes
FROM enrollments e
INNER JOIN users u ON e.user_id = u.id
INNER JOIN courses c ON e.course_id = c.id
LEFT JOIN attendance a ON a.enrollment_id = e.id AND a.date = ? AND a.marked_by = ?
WHERE e.status = 'active' AND u.role = 'student'
ORDER BY c.title, u.first_name, u.last_name
";

$stmt = $conn->prepare($students_query);
$stmt->bind_param("si", $selected_date, $instructor_id);
$stmt->execute();
$students_result = $stmt->get_result();

$students = [];
while ($row = $students_result->fetch_assoc()) {
    $students[] = $row;
}

// Get attendance statistics
$stats_query = "
    SELECT 
        COUNT(DISTINCT a.date) as total_days,
        COUNT(DISTINCT a.student_id) as total_students,
        SUM(CASE WHEN a.status = 'present' THEN 1 ELSE 0 END) as total_present,
        SUM(CASE WHEN a.status = 'absent' THEN 1 ELSE 0 END) as total_absent,
        SUM(CASE WHEN a.status = 'late' THEN 1 ELSE 0 END) as total_late,
        SUM(CASE WHEN a.status = 'excused' THEN 1 ELSE 0 END) as total_excused
    FROM attendance a
    WHERE a.marked_by = ?
";

$stmt = $conn->prepare($stats_query);
$stmt->bind_param("i", $instructor_id);
$stmt->execute();
$stats_result = $stmt->get_result();
$attendance_stats = $stats_result->fetch_assoc() ?: [
    'total_days' => 0,
    'total_students' => 0,
    'total_present' => 0,
    'total_absent' => 0,
    'total_late' => 0,
    'total_excused' => 0
];
?>

<div class="container-fluid">
    <div class="row mb-4">
        <div class="col-12">
            <div class="card">
                <div class="card-body">
                    <h5 class="card-title">Attendance Management</h5>
                    <p class="text-muted">Record and manage attendance for all enrolled students</p>
                </div>
            </div>
        </div>
    </div>
    
    <?php if ($success_message): ?>
    <div class="alert alert-success alert-dismissible fade show" role="alert">
        <i class="fas fa-check-circle me-2"></i> <?php echo $success_message; ?>
        <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
    </div>
    <?php endif; ?>
    
    <?php if ($error_message): ?>
    <div class="alert alert-danger alert-dismissible fade show" role="alert">
        <i class="fas fa-exclamation-circle me-2"></i> <?php echo $error_message; ?>
        <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
    </div>
    <?php endif; ?>
    
    <?php if (!$attendance_table_exists): ?>
    <div class="alert alert-info alert-dismissible fade show" role="alert">
        <i class="fas fa-info-circle me-2"></i> Attendance system has been set up. You can now start marking attendance for your courses.
        <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
    </div>
    <?php endif; ?>
    
    <div class="row">
        <div class="col-md-4 mb-4">
            <div class="card">
                <div class="card-header">
                    <h5 class="mb-0">Select Date</h5>
                </div>
                <div class="card-body">
                    <form method="get" action="">
                        <div class="mb-3">
                            <label for="date" class="form-label">Attendance Date</label>
                            <input type="date" name="date" id="date" class="form-control" value="<?php echo $selected_date; ?>" max="<?php echo date('Y-m-d'); ?>" required onchange="this.form.submit()">
                        </div>
                    </form>
                </div>
            </div>
            
            <div class="card mt-4">
                <div class="card-header">
                    <h5 class="mb-0">Attendance Statistics</h5>
                </div>
                <div class="card-body">
                    <div class="row text-center">
                        <div class="col-6 mb-3">
                            <h6 class="text-muted">Total Students</h6>
                            <h3><?php echo $attendance_stats['total_students']; ?></h3>
                        </div>
                        <div class="col-6 mb-3">
                            <h6 class="text-muted">Total Days</h6>
                            <h3><?php echo $attendance_stats['total_days']; ?></h3>
                        </div>
                    </div>
                    
                    <h6 class="mb-2">Attendance Summary</h6>
                    <div class="d-flex mb-2">
                        <div class="flex-grow-1">
                            <span class="badge bg-success">Present</span>
                        </div>
                        <div><?php echo $attendance_stats['total_present']; ?></div>
                    </div>
                    <div class="d-flex mb-2">
                        <div class="flex-grow-1">
                            <span class="badge bg-danger">Absent</span>
                        </div>
                        <div><?php echo $attendance_stats['total_absent']; ?></div>
                    </div>
                    <div class="d-flex mb-2">
                        <div class="flex-grow-1">
                            <span class="badge bg-warning text-dark">Late</span>
                        </div>
                        <div><?php echo $attendance_stats['total_late']; ?></div>
                    </div>
                    <div class="d-flex">
                        <div class="flex-grow-1">
                            <span class="badge bg-info">Excused</span>
                        </div>
                        <div><?php echo $attendance_stats['total_excused']; ?></div>
                    </div>
                </div>
            </div>
        </div>
        
        <div class="col-md-8">
            <?php if (empty($students)): ?>
            <div class="alert alert-warning">
                <i class="fas fa-exclamation-triangle me-2"></i> No students are currently enrolled in any courses.
            </div>
            <?php else: ?>
            <div class="card">
                <div class="card-header d-flex justify-content-between align-items-center">
                    <h5 class="mb-0">Student Attendance for <?php echo date('F d, Y', strtotime($selected_date)); ?></h5>
                    <div>
                        <button type="button" id="selectAllPresent" class="btn btn-sm btn-success me-1">
                            <i class="fas fa-check me-1"></i> All Present
                        </button>
                        <button type="button" id="clearAll" class="btn btn-sm btn-secondary">
                            <i class="fas fa-undo me-1"></i> Reset
                        </button>
                    </div>
                </div>
                <div class="card-body">
                    <form method="post" action="" id="attendanceForm">
                        <input type="hidden" name="attendance_date" value="<?php echo $selected_date; ?>">
                        
                        <div class="table-responsive">
                            <table class="table table-hover" id="attendanceTable">
                                <thead>
                                    <tr>
                                        <th width="40">#</th>
                                        <th>Student</th>
                                        <th>Course</th>
                                        <th width="120">Status</th>
                                        <th width="200">Notes</th>
                                    </tr>
                                </thead>
                                <tbody>
                                    <?php $count = 1; foreach ($students as $student): ?>
                                    <tr>
                                        <td><?php echo $count++; ?></td>
                                        <td>
                                            <div class="d-flex align-items-center">
                                                <div class="me-3">
                                                    <img src="<?php echo !empty($student['profile_image']) ? '../' . $student['profile_image'] : '../assets/img/default-avatar.png'; ?>" 
                                                         class="rounded-circle" alt="Profile" style="width: 40px; height: 40px; object-fit: cover;">
                                                </div>
                                                <div>
                                                    <h6 class="mb-0"><?php echo htmlspecialchars($student['first_name'] . ' ' . $student['last_name']); ?></h6>
                                                    <small class="text-muted"><?php echo htmlspecialchars($student['email']); ?></small>
                                                </div>
                                            </div>
                                        </td>
                                        <td>
                                            <?php echo htmlspecialchars($student['course_title']); ?>
                                        </td>
                                        <td>
                                            <input type="hidden" name="attendance[<?php echo $student['enrollment_id']; ?>][id]" value="<?php echo $student['id']; ?>">
                                            <input type="hidden" name="attendance[<?php echo $student['enrollment_id']; ?>][course_id]" value="<?php echo $student['course_id']; ?>">
                                            <select name="attendance[<?php echo $student['enrollment_id']; ?>][status]" class="form-select form-select-sm attendance-status">
                                                <option value="">-- Select --</option>
                                                <option value="present" <?php echo ($student['attendance_status'] == 'present') ? 'selected' : ''; ?>>Present</option>
                                                <option value="absent" <?php echo ($student['attendance_status'] == 'absent') ? 'selected' : ''; ?>>Absent</option>
                                                <option value="late" <?php echo ($student['attendance_status'] == 'late') ? 'selected' : ''; ?>>Late</option>
                                                <option value="excused" <?php echo ($student['attendance_status'] == 'excused') ? 'selected' : ''; ?>>Excused</option>
                                            </select>
                                        </td>
                                        <td>
                                            <input type="text" name="attendance[<?php echo $student['enrollment_id']; ?>][notes]" 
                                                   class="form-control form-control-sm" placeholder="Optional notes" 
                                                   value="<?php echo htmlspecialchars($student['notes'] ?? ''); ?>">
                                        </td>
                                    </tr>
                                    <?php endforeach; ?>
                                </tbody>
                            </table>
                        </div>
                        
                        <div class="d-grid gap-2 d-md-flex justify-content-md-end mt-4">
                            <button type="submit" name="submit_attendance" class="btn btn-primary">
                                <i class="fas fa-save me-2"></i> Save Attendance
                            </button>
                        </div>
                    </form>
                </div>
            </div>
            <?php endif; ?>
        </div>
    </div>
</div>

<script>
document.addEventListener('DOMContentLoaded', function() {
    // Select all present button
    const selectAllPresentBtn = document.getElementById('selectAllPresent');
    if (selectAllPresentBtn) {
        selectAllPresentBtn.addEventListener('click', function() {
            document.querySelectorAll('.attendance-status').forEach(select => {
                select.value = 'present';
            });
        });
    }
    
    // Clear all button
    const clearAllBtn = document.getElementById('clearAll');
    if (clearAllBtn) {
        clearAllBtn.addEventListener('click', function() {
            document.querySelectorAll('.attendance-status').forEach(select => {
                select.value = '';
            });
            document.querySelectorAll('input[type="text"]').forEach(input => {
                input.value = '';
            });
        });
    }
    
    // Initialize DataTable for better user experience with many students
    if (typeof $.fn.DataTable !== 'undefined') {
        $('#attendanceTable').DataTable({
            "paging": true,
            "lengthChange": true,
            "searching": true,
            "ordering": true,
            "info": true,
            "autoWidth": false,
            "responsive": true,
            "lengthMenu": [[10, 25, 50, -1], [10, 25, 50, "All"]]
        });
    }
});
</script>

<?php
// Include footer
include_once 'includes/footer.php';
?>