sub _timestamp {
    my $t = shift;        # allow me to pass in a time
    $t = time unless $t;  # use the current time if none specified
    
    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($t);

    my $timestamp = sprintf("%04u-%02u-%02u %02u:%02u:%02u",
        $year + 1900, $mon + 1, $mday, $hour, $min, $sec);

    return $timestamp;
}