function format_date($time){
    $t=time()-$time;
    $f=array(
        '31536000'=>'년',
        '2592000'=>'개월',
        '604800'=>'주',
        '86400'=>'일',
        '3600'=>'시간',
        '60'=>'분',
        '1'=>'초'
    );
    foreach ($f as $k=>$v)    {
        if (0 !=$c=floor($t/(int)$k)) {
            return $c.$v.'전';
        }
    }
}