Sample SMF code

// Put this user in the online log.
function writeLog($force = false)
{
    global $user_info, $user_settings, $context, $modSettings, $settings, $topic, $board, $smcFunc, $sourcedir;

    // If we are showing who is viewing a topic, let's see if we are, and force an update if so - to make it accurate.
    if (!empty($settings['display_who_viewing']) && ($topic || $board))
    {
        // Take the opposite approach!
        $force = true;
        // Don't update for every page - this isn't wholly accurate but who cares.
        if ($topic)
        {
            if (isset($_SESSION['last_topic_id']) && $_SESSION['last_topic_id'] == $topic)
                $force = false;
            $_SESSION['last_topic_id'] = $topic;
        }
    }

    // Are they a spider we should be tracking? Mode = 1 gets tracked on its spider check...
    if (!empty($user_info['possibly_robot']) && !empty($modSettings['spider_mode']) && $modSettings['spider_mode'] > 1)
    {
        require_once($sourcedir . '/ManageSearchEngines.php');
        logSpider();
    }

    // Don't mark them as online more than every so often.
    if (!empty($_SESSION['log_time']) && $_SESSION['log_time'] >= (time() - 8) && !$force)
        return;

    if (!empty($modSettings['who_enabled']))
    {
        $serialized = $_GET + array('USER_AGENT' => $_SERVER['HTTP_USER_AGENT']);

        // In the case of a dlattach action, session_var may not be set.
        if (!isset($context['session_var']))
            $context['session_var'] = $_SESSION['session_var'];

        unset($serialized['sesc'], $serialized[$context['session_var']]);
        $serialized = serialize($serialized);
    }
    else
        $serialized = '';

    // Guests use 0, members use their session ID.
    $session_id = $user_info['is_guest'] ? 'ip' . $user_info['ip'] : session_id();

    // Grab the last all-of-SMF-specific log_online deletion time.
    $do_delete = cache_get_data('log_online-update', 30) < time() - 30;

    // If the last click wasn't a long time ago, and there was a last click...
    if (!empty($_SESSION['log_time']) && $_SESSION['log_time'] >= time() - $modSettings['lastActive'] * 20)
    {
        if ($do_delete)
        {
            $smcFunc['db_query']('delete_log_online_interval', '
                DELETE FROM {db_prefix}log_online
                WHERE log_time < {int:log_time}
                    AND session != {string:session}',
                array(
                    'log_time' => time() - $modSettings['lastActive'] * 60,
                    'session' => $session_id,
                )
            );

            // Cache when we did it last.
            cache_put_data('log_online-update', time(), 30);
        }

        $smcFunc['db_query']('', '
            UPDATE {db_prefix}log_online
            SET log_time = {int:log_time}, ip = IFNULL(INET_ATON({string:ip}), 0), url = {string:url}
            WHERE session = {string:session}',
            array(
                'log_time' => time(),
                'ip' => $user_info['ip'],
                'url' => $serialized,
                'session' => $session_id,
            )
        );

        // Guess it got deleted.
        if ($smcFunc['db_affected_rows']() == 0)
            $_SESSION['log_time'] = 0;
    }
    else
        $_SESSION['log_time'] = 0;

    // Otherwise, we have to delete and insert.
    if (empty($_SESSION['log_time']))
    {
        if ($do_delete || !empty($user_info['id']))
            $smcFunc['db_query']('', '
                DELETE FROM {db_prefix}log_online
                WHERE ' . ($do_delete ? 'log_time < {int:log_time}' : '') . ($do_delete && !empty($user_info['id']) ? ' OR ' : '') . (empty($user_info['id']) ? '' : 'id_member = {int:current_member}'),
                array(
                    'current_member' => $user_info['id'],
                    'log_time' => time() - $modSettings['lastActive'] * 60,
                )
            );

        $smcFunc['db_insert']($do_delete ? 'ignore' : 'replace',
            '{db_prefix}log_online',
            array('session' => 'string', 'id_member' => 'int', 'id_spider' => 'int', 'log_time' => 'int', 'ip' => 'raw', 'url' => 'string'),
            array($session_id, $user_info['id'], empty($_SESSION['id_robot']) ? 0 : $_SESSION['id_robot'], time(), 'IFNULL(INET_ATON(\'' . $user_info['ip'] . '\'), 0)', $serialized),
            array('session')
        );
    }

    // Mark your session as being logged.
    $_SESSION['log_time'] = time();

    // Well, they are online now.
    if (empty($_SESSION['timeOnlineUpdated']))
        $_SESSION['timeOnlineUpdated'] = time();

    // Set their login time, if not already done within the last minute.
    if (SMF != 'SSI' && !empty($user_info['last_login']) && $user_info['last_login'] < time() - 60)
    {
        // Don't count longer than 15 minutes.
        if (time() - $_SESSION['timeOnlineUpdated'] > 60 * 15)
            $_SESSION['timeOnlineUpdated'] = time();

        $user_settings['total_time_logged_in'] += time() - $_SESSION['timeOnlineUpdated'];
        updateMemberData($user_info['id'], array('last_login' => time(), 'member_ip' => $user_info['ip'], 'member_ip2' => $_SERVER['BAN_CHECK_IP'], 'total_time_logged_in' => $user_settings['total_time_logged_in']));

        if (!empty($modSettings['cache_enable']) && $modSettings['cache_enable'] >= 2)
            cache_put_data('user_settings-' . $user_info['id'], $user_settings, 60);

        $user_info['total_time_logged_in'] += time() - $_SESSION['timeOnlineUpdated'];
        $_SESSION['timeOnlineUpdated'] = time();
    }
}