Counter Visits Anti Bot Sharing Facebook

Question

I created a counter of visits, but, we need that there is no count through the visits for reading the bots, mainly of facebook.

This code is called via Ajax, after the user is on the page by 5 seconds.

Even so, when sharing the page and facebook read the information, still a visit is accounted for.

    $contador = &$_COOKIE['contador'.$album_id];
    if ( !$contador )
    {
        if (preg_match('~(bot|crawl)~i', $_SERVER["HTTP_USER_AGENT"])) {
          echo 'bot';
        } else {
            if (
                strpos($_SERVER["HTTP_USER_AGENT"], "facebookexternalhit/") !== false ||          
                strpos($_SERVER["HTTP_USER_AGENT"], "Facebot") !== false
            )
            {
                echo 'bot';
            }
            else
            {
                setcookie('contador'.$album_id, true, time() + (  3600*24*7 ) ); 
               //insert no banco
            }
        }
    }
    else
    {
        echo 'ja visitou';
    }
}