#!/usr/bin/perl
use strict;
use warnings;
use Date::Calc qw/Days_in_Month Day_of_Week/;

my @days_of_week = qw/NULL Mon Tue Wed Thu Fri Sat Sun/;

my $i=0;
# Our 14 calendars are in these years, this century
# see: http://www.koshko.com/calendar/calendar-lookup-gregorian.shtml
for (6, 7, 1, 2, 3, 10, 11, 12, 24, 8, 20, 4, 16, 0) {
  my $year=$_+2000;
  $i++;

  my %days_of_month;

  for my $month_of_year(1 .. 12) {
    my $sday = Day_of_Week($year,$month_of_year,1); # only need to call this once
    for my $day_of_month(1 .. Days_in_Month($year,$month_of_year)) {
      $sday = 1 if($sday>7);
      my $dow = $sday++;
      $days_of_month{$day_of_month}{$dow}++;
    }   
  }

  for my $day_of_month (sort keys %days_of_month) {
    next if(scalar keys %{$days_of_month{$day_of_month}} == 7); 
    my @missing_days;
    for (1..7) {
      push (@missing_days, $days_of_week[$_]) if !defined $days_of_month{$day_of_month}{$_};
    }   
    print "Calendar $i: In $year, Day $day_of_month does not fall on ", join(", ", @missing_days), "\n";
  }
}