// In your login processing code:
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = clean_input($_POST['username']);
    $password = clean_input($_POST['password']);
    $is_admin = isset($_POST['is_admin']) ? true : false;
    
    if ($is_admin) {
        $result = login_admin($username, $password);
        if ($result['success']) {
            header("Location: admin/dashboard.php");
            exit();
        } else {
            $error = "Admin login failed: " . $result['message'];
        }
    } else {
        $result = login_user($username, $password);
        if ($result['success']) {
            header("Location: user/dashboard.php");
            exit();
        } else {
            $error = "Login failed: " . $result['message'];
        }
    }
}