my $start_dt = shift;
my $end_dt = shift;
if ( $start_dt->compare($end_dt) > 0 ) {
# swap dates
my $int_dt = $end_dt;
$end_dt = $start_dt;
$start_dt = $int_dt;
}
# start and end should not be closed days
my $days = $start_dt->delta_days($end_dt)->delta_days;
-