
<?php

function is_active($page_name) {
    $page = $_GET['page'] ?? 'dashboard';
    return $page === $page_name ? 'active' : '';
}

function get_page_title() {
    $page = $_GET['page'] ?? 'dashboard';
    return ucfirst($page);
}

function get_all_murid() {
    $pdo = db();
    $stmt = $pdo->query("SELECT m.id, m.nis, m.nisn, m.nama_lengkap, m.jenis_kelamin, m.email, m.foto, k.nama_kelas 
                         FROM murid m
                         LEFT JOIN kelas k ON m.kelas_id = k.id
                         ORDER BY m.nama_lengkap ASC");
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_murid_by_id($id) {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM murid WHERE id = ?");
    $stmt->execute([$id]);
    return $stmt->fetch(PDO::FETCH_ASSOC);
}

function handle_murid_action() {
    $action = $_POST['action'] ?? $_GET['action'] ?? '';

    // Handle Delete Action via GET first as it redirects
    if ($action === 'delete' && isset($_GET['id'])) {
        $id = $_GET['id'];
        $murid = get_murid_by_id($id); // Get murid data to delete foto
        $pdo = db();
        try {
            // Delete old photo if exists
            if (!empty($murid['foto'])) {
                $photo_path = 'assets/uploads/murid/' . $murid['foto'];
                if (file_exists($photo_path)) {
                    unlink($photo_path);
                }
            }
            $stmt = $pdo->prepare("DELETE FROM murid WHERE id = ?");
            $stmt->execute([$id]);
            header("Location: index.php?page=murid&status=deleted");
            exit();
        } catch (PDOException $e) {
            header("Location: index.php?page=murid&status=error");
            exit();
        }
    }
    
    // Only proceed with POST actions from here
    if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
        return null;
    }

    $pdo = db();
    $id = $_POST['id'] ?? null;

    // Handle Import
    if ($action === 'import') {
        if (isset($_FILES['file_murid']) && $_FILES['file_murid']['error'] === UPLOAD_ERR_OK) {
            $file_tmp_path = $_FILES['file_murid']['tmp_name'];
            return import_murid_from_xlsx($file_tmp_path);
        } else {
            return ['success' => false, 'message' => 'Gagal mengunggah file. Silakan coba lagi.'];
        }
    }
    
    // Handle Add/Edit
    $nis = $_POST['nis'] ?? '';
    $nisn = $_POST['nisn'] ?? '';
    $nama_lengkap = $_POST['nama_lengkap'] ?? '';
    $tempat_lahir = $_POST['tempat_lahir'] ?? '';
    $tanggal_lahir = $_POST['tanggal_lahir'] ?? '';
    $jenis_kelamin = $_POST['jenis_kelamin'] ?? '';
    $alamat = $_POST['alamat'] ?? '';
    $latitude = $_POST['latitude'] ?? '';
    $longitude = $_POST['longitude'] ?? '';
    $no_telepon = $_POST['no_telepon'] ?? '';
    $email = $_POST['email'] ?? '';
    $kelas_id = !empty($_POST['kelas_id']) ? $_POST['kelas_id'] : null;

    
    $foto_filename = $_POST['foto_existing'] ?? null;

    // Handle file upload
    if (isset($_FILES['foto']) && $_FILES['foto']['error'] === UPLOAD_ERR_OK) {
        $upload_dir = 'assets/uploads/murid/';
        if (!is_dir($upload_dir)) {
            mkdir($upload_dir, 0777, true);
        }

        $tmp_name = $_FILES['foto']['tmp_name'];
        $original_name = basename($_FILES['foto']['name']);
        $file_ext = strtolower(pathinfo($original_name, PATHINFO_EXTENSION));
        $safe_filename = preg_replace('/[^A-Za-z0-9_.-]/', '_', pathinfo($original_name, PATHINFO_FILENAME));
        $foto_filename = uniqid() . '_' . $safe_filename . '.' . $file_ext;
        
        // Delete old photo if a new one is uploaded during edit
        if ($action === 'edit' && !empty($_POST['foto_existing'])) {
            $old_photo_path = $upload_dir . $_POST['foto_existing'];
            if (file_exists($old_photo_path)) {
                unlink($old_photo_path);
            }
        }

        if (!move_uploaded_file($tmp_name, $upload_dir . $foto_filename)) {
             return ['success' => false, 'message' => 'Gagal memindahkan file foto.'];
        }
    }

    try {
        if ($action === 'add') {
            $stmt = $pdo->prepare(
                "INSERT INTO murid (nis, nisn, nama_lengkap, tempat_lahir, tanggal_lahir, jenis_kelamin, alamat, foto, latitude, longitude, no_telepon, email, kelas_id) 
                 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"
            );
            $stmt->execute([$nis, $nisn, $nama_lengkap, $tempat_lahir, $tanggal_lahir, $jenis_kelamin, $alamat, $foto_filename, $latitude, $longitude, $no_telepon, $email, $kelas_id]);
            return ['success' => true, 'message' => 'Data murid berhasil ditambahkan.'];
        } elseif ($action === 'edit' && $id) {
            $stmt = $pdo->prepare(
                "UPDATE murid SET nis = ?, nisn = ?, nama_lengkap = ?, tempat_lahir = ?, tanggal_lahir = ?, 
                 jenis_kelamin = ?, alamat = ?, foto = ?, latitude = ?, longitude = ?, no_telepon = ?, email = ?, kelas_id = ? WHERE id = ?"
            );
            $stmt->execute([$nis, $nisn, $nama_lengkap, $tempat_lahir, $tanggal_lahir, $jenis_kelamin, $alamat, $foto_filename, $latitude, $longitude, $no_telepon, $email, $kelas_id, $id]);
            return ['success' => true, 'message' => 'Data murid berhasil diperbarui.'];
        }
    } catch (PDOException $e) {
        if ($e->getCode() == 23000) { // Integrity constraint violation
            return ['success' => false, 'message' => 'Gagal menyimpan data. NIS atau NISN sudah terdaftar.'];
        }
        return ['success' => false, 'message' => 'Terjadi kesalahan database: ' . $e->getMessage()];
    }

    return null;
}

function import_murid_from_xlsx($filepath) {
    // Include the parser library
    require_once 'libs/SimpleXLSX.php';

    // Check if the file exists and is readable
    if (!file_exists($filepath) || !is_readable($filepath)) {
        return ['success' => false, 'message' => 'File tidak ditemukan atau tidak bisa dibaca.'];
    }

    // Try to parse the XLSX file
    if ($xlsx = Shuchkin\SimpleXLSX::parse($filepath)) {
        $pdo = db();
        $success_count = 0;
        $fail_count = 0;
        $errors = [];

        // Get rows as array
        $rows = $xlsx->rows();
        
        // Skip header row (the first row)
        $is_header = true;

        foreach ($rows as $row) {
            if ($is_header) {
                $is_header = false;
                continue;
            }

            // Assign columns to variables - assuming order: NIS, NISN, Nama, Tgl Lahir, Alamat
            $nis = $row[0] ?? '';
            $nisn = $row[1] ?? '';
            $nama_lengkap = $row[2] ?? '';
            $tanggal_lahir = $row[3] ?? '';
            $alamat = $row[4] ?? '';
            
            // Basic validation: skip if NIS or name is empty
            if (empty($nis) || empty($nama_lengkap)) {
                $fail_count++;
                $errors[] = "Baris data dengan NIS '.htmlspecialchars($nis).' dan Nama '.htmlspecialchars($nama_lengkap).' dilewati karena data tidak lengkap.";
                continue;
            }

            try {
                // Using the existing add function logic
                $stmt = $pdo->prepare(
                    "INSERT INTO murid (nis, nisn, nama_lengkap, tanggal_lahir, alamat) 
                     VALUES (?, ?, ?, ?, ?)"
                );
                $stmt->execute([$nis, $nisn, $nama_lengkap, $tanggal_lahir, $alamat]);
                $success_count++;
            } catch (PDOException $e) {
                $fail_count++;
                 if ($e->getCode() == 23000) {
                    $errors[] = "NIS atau NISN '.htmlspecialchars($nis).' sudah ada di database.";
                } else {
                    $errors[] = "Gagal memasukkan data untuk NIS '.htmlspecialchars($nis).': " . $e->getMessage();
                }
            }
        }
        
        $message = "Impor selesai. Berhasil: {$success_count}, Gagal: {$fail_count}.";
        if (!empty($errors)) {
            $message .= "<br>Detail kegagalan:<br>" . implode("<br>", $errors);
        }
        
        return ['success' => ($fail_count === 0), 'message' => $message];
        
    } else {
        return ['success' => false, 'message' => 'Gagal memproses file XLSX: ' . Shuchkin\SimpleXLSX::parseError()];
    }
}

function get_all_guru() {
    $pdo = db();
    $stmt = $pdo->query("SELECT id, nip, nama, foto FROM guru ORDER BY nama ASC");
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_guru_by_id($id) {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM guru WHERE id = ?");
    $stmt->execute([$id]);
    return $stmt->fetch(PDO::FETCH_ASSOC);
}

function handle_guru_action() {
    $action = $_POST['action'] ?? $_GET['action'] ?? '';

    if ($action === 'delete' && isset($_GET['id'])) {
        $id = $_GET['id'];
        $guru = get_guru_by_id($id);
        $pdo = db();
        try {
            if (!empty($guru['foto'])) {
                $photo_path = 'assets/uploads/guru/' . $guru['foto'];
                if (file_exists($photo_path)) {
                    unlink($photo_path);
                }
            }
            $stmt = $pdo->prepare("DELETE FROM guru WHERE id = ?");
            $stmt->execute([$id]);
            header("Location: index.php?page=teachers&status=deleted");
            exit();
        } catch (PDOException $e) {
            header("Location: index.php?page=teachers&status=error");
            exit();
        }
    }

    if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
        return null;
    }

    $pdo = db();
    $id = $_POST['id'] ?? null;
    $nip = $_POST['nip'] ?? '';
    $nama = $_POST['nama'] ?? '';
    $alamat = $_POST['alamat'] ?? '';
    $telepon = $_POST['telepon'] ?? '';
    $latitude = $_POST['latitude'] ?? '';
    $longitude = $_POST['longitude'] ?? '';
    
    $foto_filename = $_POST['foto_existing'] ?? null;

    if (isset($_FILES['foto']) && $_FILES['foto']['error'] === UPLOAD_ERR_OK) {
        $upload_dir = 'assets/uploads/guru/';
        if (!is_dir($upload_dir)) {
            mkdir($upload_dir, 0777, true);
        }

        $tmp_name = $_FILES['foto']['tmp_name'];
        $original_name = basename($_FILES['foto']['name']);
        $file_ext = strtolower(pathinfo($original_name, PATHINFO_EXTENSION));
        $safe_filename = preg_replace('/[^A-Za-z0-9_.-]/', '_', pathinfo($original_name, PATHINFO_FILENAME));
        $foto_filename = uniqid() . '_' . $safe_filename . '.' . $file_ext;
        
        if ($action === 'edit' && !empty($_POST['foto_existing'])) {
            $old_photo_path = $upload_dir . $_POST['foto_existing'];
            if (file_exists($old_photo_path)) {
                unlink($old_photo_path);
            }
        }

        if (!move_uploaded_file($tmp_name, $upload_dir . $foto_filename)) {
             return ['success' => false, 'message' => 'Gagal memindahkan file foto.'];
        }
    }

    try {
        if ($action === 'add') {
            $stmt = $pdo->prepare(
                "INSERT INTO guru (nip, nama, alamat, telepon, foto, latitude, longitude) 
                 VALUES (?, ?, ?, ?, ?, ?, ?)"
            );
            $stmt->execute([$nip, $nama, $alamat, $telepon, $foto_filename, $latitude, $longitude]);
            return ['success' => true, 'message' => 'Data guru berhasil ditambahkan.'];
        } elseif ($action === 'edit' && $id) {
            $stmt = $pdo->prepare(
                "UPDATE guru SET nip = ?, nama = ?, alamat = ?, telepon = ?, foto = ?, latitude = ?, longitude = ? WHERE id = ?"
            );
            $stmt->execute([$nip, $nama, $alamat, $telepon, $foto_filename, $latitude, $longitude, $id]);
            return ['success' => true, 'message' => 'Data guru berhasil diperbarui.'];
        }
    } catch (PDOException $e) {
        if ($e->getCode() == 23000) { // Integrity constraint violation
            return ['success' => false, 'message' => 'Gagal menyimpan data. NIP sudah terdaftar.'];
        }
        return ['success' => false, 'message' => 'Terjadi kesalahan database: ' . $e->getMessage()];
    }

    return null;
}

function get_all_kelas() {
    $pdo = db();
    $stmt = $pdo->query("
        SELECT k.id, k.nama_kelas, g.nama as nama_wali_kelas
        FROM kelas k
        LEFT JOIN guru g ON k.id_wali_kelas = g.id
        ORDER BY k.nama_kelas ASC
    ");
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_kelas_by_id($id) {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM kelas WHERE id = ?");
    $stmt->execute([$id]);
    return $stmt->fetch(PDO::FETCH_ASSOC);
}

function handle_kelas_action() {
    $action = $_POST['action'] ?? $_GET['action'] ?? '';

    if ($action === 'delete' && isset($_GET['id'])) {
        $id = $_GET['id'];
        $pdo = db();
        try {
            $stmt = $pdo->prepare("DELETE FROM kelas WHERE id = ?");
            $stmt->execute([$id]);
            header("Location: index.php?page=classes&status=deleted");
            exit();
        } catch (PDOException $e) {
            // Foreign key constraint might fail, though ON DELETE SET NULL should prevent it.
            // Good to have a generic error handler.
            header("Location: index.php?page=classes&status=error");
            exit();
        }
    }

    if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
        return null;
    }

    $pdo = db();
    $id = $_POST['id'] ?? null;
    $nama_kelas = $_POST['nama_kelas'] ?? '';
    // Use 'none' or null for the wali kelas if not selected
    $id_wali_kelas = !empty($_POST['id_wali_kelas']) ? $_POST['id_wali_kelas'] : null;

    try {
        if ($action === 'add') {
            $stmt = $pdo->prepare(
                "INSERT INTO kelas (nama_kelas, id_wali_kelas) VALUES (?, ?)"
            );
            $stmt->execute([$nama_kelas, $id_wali_kelas]);
            return ['success' => true, 'message' => 'Data kelas berhasil ditambahkan.'];
        } elseif ($action === 'edit' && $id) {
            $stmt = $pdo->prepare(
                "UPDATE kelas SET nama_kelas = ?, id_wali_kelas = ? WHERE id = ?"
            );
            $stmt->execute([$nama_kelas, $id_wali_kelas, $id]);
            return ['success' => true, 'message' => 'Data kelas berhasil diperbarui.'];
        }
    } catch (PDOException $e) {
        if ($e->getCode() == 23000) {
            return ['success' => false, 'message' => 'Gagal menyimpan data. Nama kelas mungkin sudah ada.'];
        }
        return ['success' => false, 'message' => 'Terjadi kesalahan database: ' . $e->getMessage()];
    }

    return null;
}


function get_all_jadwal() {
    $pdo = db();
    $stmt = $pdo->query("
        SELECT 
            j.id, 
            j.hari, 
            j.jam_mulai, 
            j.jam_selesai, 
            mp.nama_matapelajaran,
            k.nama_kelas,
            g.nama as nama_guru
        FROM jadwal j
        JOIN kelas k ON j.id_kelas = k.id
        JOIN guru g ON j.id_guru = g.id
        LEFT JOIN mata_pelajaran mp ON j.id_matapelajaran = mp.id
        ORDER BY k.nama_kelas, FIELD(j.hari, 'Senin', 'Selasa', 'Rabu', 'Kamis', 'Jumat', 'Sabtu', 'Minggu'), j.jam_mulai
    ");
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_jadwal_by_id($id) {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM jadwal WHERE id = ?");
    $stmt->execute([$id]);
    return $stmt->fetch(PDO::FETCH_ASSOC);
}

function handle_jadwal_action() {
    $action = $_POST['action'] ?? $_GET['action'] ?? '';

    if ($action === 'delete' && isset($_GET['id'])) {
        $id = $_GET['id'];
        $pdo = db();
        try {
            $stmt = $pdo->prepare("DELETE FROM jadwal WHERE id = ?");
            $stmt->execute([$id]);
            header("Location: index.php?page=schedule&status=deleted");
            exit();
        } catch (PDOException $e) {
            header("Location: index.php?page=schedule&status=error");
            exit();
        }
    }

    if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
        return null;
    }

    $pdo = db();
    $id = $_POST['id'] ?? null;
    $id_kelas = $_POST['id_kelas'] ?? '';
    $id_guru = $_POST['id_guru'] ?? '';
    $id_matapelajaran = $_POST['id_matapelajaran'] ?? ''; // New field
    $hari = $_POST['hari'] ?? '';
    $jam_mulai = $_POST['jam_mulai'] ?? '';
    $jam_selesai = $_POST['jam_selesai'] ?? '';

    // Basic validation
    if (empty($id_kelas) || empty($id_guru) || empty($id_matapelajaran) || empty($hari) || empty($jam_mulai) || empty($jam_selesai)) {
        return ['success' => false, 'message' => 'Semua kolom wajib diisi.'];
    }

    try {
        if ($action === 'add') {
            $stmt = $pdo->prepare(
                "INSERT INTO jadwal (id_kelas, id_guru, id_matapelajaran, hari, jam_mulai, jam_selesai) 
                 VALUES (?, ?, ?, ?, ?, ?)"
            );
            $stmt->execute([$id_kelas, $id_guru, $id_matapelajaran, $hari, $jam_mulai, $jam_selesai]);
            return ['success' => true, 'message' => 'Data jadwal berhasil ditambahkan.'];
        } elseif ($action === 'edit' && $id) {
            $stmt = $pdo->prepare(
                "UPDATE jadwal SET id_kelas = ?, id_guru = ?, id_matapelajaran = ?, hari = ?, jam_mulai = ?, jam_selesai = ? 
                 WHERE id = ?"
            );
            $stmt->execute([$id_kelas, $id_guru, $id_matapelajaran, $hari, $jam_mulai, $jam_selesai, $id]);
            return ['success' => true, 'message' => 'Data jadwal berhasil diperbarui.'];
        }
    } catch (PDOException $e) {
        return ['success' => false, 'message' => 'Terjadi kesalahan database: ' . $e->getMessage()];
    }

    return null;
}

// Attendance Functions

function get_murid_by_kelas($kelas_id) {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT id, nama_lengkap FROM murid WHERE kelas_id = ? ORDER BY nama_lengkap ASC");
    $stmt->execute([$kelas_id]);
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_jadwal_by_kelas_and_hari($kelas_id, $hari) {
    $pdo = db();
    $stmt = $pdo->prepare("
        SELECT j.id, mp.nama_matapelajaran, j.jam_mulai, j.jam_selesai 
        FROM jadwal j
        LEFT JOIN mata_pelajaran mp ON j.id_matapelajaran = mp.id
        WHERE j.id_kelas = ? AND j.hari = ? ORDER BY j.jam_mulai ASC");
    $stmt->execute([$kelas_id, $hari]);
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_absensi($id_kelas, $tanggal) {
    $pdo = db();
    $stmt = $pdo->prepare("
        SELECT murid_id, jadwal_id, status
        FROM absensi
        WHERE tanggal = ? AND jadwal_id IN (SELECT id FROM jadwal WHERE id_kelas = ?)
    ");
    $stmt->execute([$tanggal, $id_kelas]);
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);

    // Format the result for easier lookup in the template
    $absensi_data = [];
    foreach ($result as $row) {
        $absensi_data[$row['murid_id']][$row['jadwal_id']] = $row['status'];
    }
    return $absensi_data;
}

function handle_absensi_action() {
    if ($_SERVER['REQUEST_METHOD'] !== 'POST' || !isset($_POST['action']) || $_POST['action'] !== 'save_absensi') {
        return null;
    }

    $id_kelas = $_POST['id_kelas'] ?? '';
    $tanggal = $_POST['tanggal'] ?? '';
    $absensi = $_POST['absensi'] ?? [];

    if (empty($id_kelas) || empty($tanggal) || empty($absensi)) {
        return ['success' => false, 'message' => 'Data tidak lengkap. Harap pilih kelas, tanggal, dan isi absensi.'];
    }

    $pdo = db();
    try {
        $pdo->beginTransaction();

        // Prepare statement for inserting/updating attendance
        $stmt = $pdo->prepare("
            INSERT INTO absensi (jadwal_id, murid_id, tanggal, status) 
            VALUES (:jadwal_id, :murid_id, :tanggal, :status)
            ON DUPLICATE KEY UPDATE status = :status
        ");

        foreach ($absensi as $murid_id => $jadwal_absensi) {
            foreach ($jadwal_absensi as $jadwal_id => $status) {
                if (!empty($status)) {
                    $stmt->execute([
                        ':jadwal_id' => $jadwal_id,
                        ':murid_id' => $murid_id,
                        ':tanggal' => $tanggal,
                        ':status' => $status
                    ]);
                }
            }
        }

        $pdo->commit();
        return ['success' => true, 'message' => 'Absensi berhasil disimpan.'];

    } catch (PDOException $e) {
        $pdo->rollBack();
        return ['success' => false, 'message' => 'Gagal menyimpan absensi: ' . $e->getMessage()];
    }
}

function get_rekap_absensi($id_kelas, $start_date, $end_date) {
    $pdo = db();
    
    // Validate input dates
    if (empty($id_kelas) || empty($start_date) || empty($end_date)) {
        return [];
    }

    $sql = "
        SELECT 
            m.id as murid_id,
            m.nis,
            m.nama_lengkap,
            COUNT(a.id) as total_absensi,
            SUM(CASE WHEN a.status = 'Hadir' THEN 1 ELSE 0 END) as total_hadir,
            SUM(CASE WHEN a.status = 'Sakit' THEN 1 ELSE 0 END) as total_sakit,
            SUM(CASE WHEN a.status = 'Izin' THEN 1 ELSE 0 END) as total_izin,
            SUM(CASE WHEN a.status = 'Alpa' THEN 1 ELSE 0 END) as total_alpa
        FROM murid m
        LEFT JOIN absensi a ON m.id = a.murid_id
        WHERE m.kelas_id = :id_kelas
          AND a.tanggal BETWEEN :start_date AND :end_date
        GROUP BY m.id, m.nis, m.nama_lengkap
        ORDER BY m.nama_lengkap ASC;
    ";

    try {
        $stmt = $pdo->prepare($sql);
        $stmt->execute([
            ':id_kelas' => $id_kelas,
            ':start_date' => $start_date,
            ':end_date' => $end_date
        ]);
        return $stmt->fetchAll(PDO::FETCH_ASSOC);
    } catch (PDOException $e) {
        // Log error or handle it as needed
        error_log("Rekap Absensi Error: " . $e->getMessage());
        return [];
    }
}

// Subject (Mata Pelajaran) Functions

function get_all_matapelajaran() {
    $pdo = db();
    $stmt = $pdo->query("SELECT * FROM mata_pelajaran ORDER BY nama_matapelajaran ASC");
    return $stmt->fetchAll(PDO::FETCH_ASSOC);
}

function get_matapelajaran_by_id($id) {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM mata_pelajaran WHERE id = ?");
    $stmt->execute([$id]);
    return $stmt->fetch(PDO::FETCH_ASSOC);
}

function handle_matapelajaran_action() {
    $action = $_POST['action'] ?? $_GET['action'] ?? '';

    if ($action === 'delete' && isset($_GET['id'])) {
        $id = $_GET['id'];
        $pdo = db();
        try {
            $stmt = $pdo->prepare("DELETE FROM mata_pelajaran WHERE id = ?");
            $stmt->execute([$id]);
            header("Location: index.php?page=subjects&status=deleted");
            exit();
        } catch (PDOException $e) {
            header("Location: index.php?page=subjects&status=error&err_msg=" . urlencode($e->getMessage()));
            exit();
        }
    }

    if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
        return null;
    }

    $pdo = db();
    $id = $_POST['id'] ?? null;
    $nama_matapelajaran = $_POST['nama_matapelajaran'] ?? '';

    try {
        if ($action === 'add') {
            $stmt = $pdo->prepare("INSERT INTO mata_pelajaran (nama_matapelajaran) VALUES (?)");
            $stmt->execute([$nama_matapelajaran]);
            return ['success' => true, 'message' => 'Data mata pelajaran berhasil ditambahkan.'];
        } elseif ($action === 'edit' && $id) {
            $stmt = $pdo->prepare("UPDATE mata_pelajaran SET nama_matapelajaran = ? WHERE id = ?");
            $stmt->execute([$nama_matapelajaran, $id]);
            return ['success' => true, 'message' => 'Data mata pelajaran berhasil diperbarui.'];
        }
    } catch (PDOException $e) {
        if ($e->getCode() == 23000) {
            return ['success' => false, 'message' => 'Gagal menyimpan data. Nama mata pelajaran mungkin sudah ada.'];
        }
        return ['success' => false, 'message' => 'Terjadi kesalahan database: ' . $e->getMessage()];
    }

    return null;
}

?>