use strict;
use warnings;

use POSIX       qw( strftime       );
use Time::Local qw( timegm_nocheck );


# Supplied definitions.

my $base_year  = 2004;
my $base_month = 1; # 0-based
my $base_day   = 1; # 1-based

my @weeks_in_month = (
   4, # Feb
   5, # Mar
   4, # Apr
   4, # May
   5, # Jun
   4, # Jul
   4, # Aug
   5, # Sep
   4, # Oct
   4, # Nov
   5, # Dec
   4, # Jan
);


# Derived constants.

my @days_before_month = (0);
for (0..11) {
   $days_before_month[$_+1] = $days_before_month[$_]
                            + $weeks_in_month[$_] * 7;
}

my $days_in_year = $days_before_month[12];


# The guts.

sub first_day_of_accounting_month {
   my ($year, $month) = @_;

   my $day = $base_day
           + ($year - $base_year) * $days_in_year
           + $days_before_month[$month];

   my $time = timegm_nocheck(0,0,0, $day, $base_month, $base_year);
}


sub first_day_of_accounting_year {
   push(@_, 0);
   goto &first_day_of_accounting_month;
}


# Generate a bunch of data for demo purposes.

# The output format can easily be changed.
my $date_format = '%b %d, %Y';

for my $year (2004 .. 2015) {
   my $time;

   $time = first_day_of_accounting_year($year);
   print("Accounting year $year\n");
   print(strftime($date_format, gmtime($time)) . "\n");
   print("\n");

   for my $month (0..11) { # Feb..Jan
      $time = first_day_of_accounting_month($year, $month);
      print(strftime($date_format, gmtime($time)) . "\n");
   }

   print("\n");
   print("\n");
}