Calendar.rakumod

unit module Calendar;

sub week-as-cells ( DateTime $date is copy ) is export {
    my $first-of-week = $*START-OF-WEEK // 1;

    my $start = $date.earlier(:days( ($date.day-of-week - $first-of-week) % 7 ));

    return gather {
        for 1 .. 7 {
            my $later = $start.later(:days( $_ - 1 ));

            if $later.month != $date.month {
                take Nil;
            }
            else {
                take $later;
            }
        }
    };
}

sub month-as-table ( DateTime $date = DateTime.now.truncated-to('month') ) is export {
    gather {
        my @week;
        my $this-week = $date;
        repeat {
            @week = week-as-cells( $this-week );
            take @week;
            $this-week = @week[* -1].?later(:1day);
        } until any( @week.map: { .?day // 0 } ) == $date.days-in-month;
    };
}