#!/usr/bin/perl
use strict;
use warnings;

use Date::Calc qw(:all);
use Lingua::EN::Inflect qw(ORD);

sub commify {
  local $_  = shift;
  1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
  return $_;
}

sub birth_year {
  print "What year were you born? (YYYY) ";
  chomp(my $b_year = <>);
  
  # Checking for a 4 digit year.
  if ($b_year !~ /\d{4}/) {
    print "Sorry, please use the full year.\n";
    $b_year = birth_year();
  }

  return $b_year;
}

sub birth_month {
  print "What month were you born? (MM or name) ";
  chomp(my $b_month = <>);

  # This is language specific for English.
  if ($b_month =~ /[a-z]+/i) {
    $b_month = Decode_Month($b_month,1);
    
    # If the month doesn't match, it will try again.
    # Decode_Month had error checking in mind.
    if ($b_month =~ /0/) {
      print "Sorry, that is not a month.\n";
      $b_month = birth_month();
    }
  }
  return $b_month;
}

sub birth_day {
  my ($b_year,$b_month) = @_;
  my $month_name = Month_to_Text($b_month);
  
  print "What day were you born? (DD) ";
  chomp(my $b_day = <>);
  
  # Checking for 0.
  if (!$b_day or $b_day == 0) {
    print "Sorry, you did not specify a date.\n";
    $b_day = birth_day($b_year,$b_month);
  }

  # Checking days for February first.
  elsif ($b_month =~ /^(0?[2])$/) {
    if ($b_year % 4 == 0 && $b_day > 29) {
      print "Sorry, $month_name in $b_year only had 29 days.\n";
      $b_day = birth_day($b_year,$b_month);
    }
    elsif ($b_day > 28) {
      print "Sorry, $month_name in $b_year only had 28 days.\n";
      $b_day = birth_day($b_year,$b_month);
    }
  }

  # Checking for the months with 31 days.
  elsif ($b_month =~ /^(0?[13578]|1[02])$/ && $b_day > 31) {
    print "Sorry, $month_name only has 31 days.\n";
    $b_day = birth_day($b_year,$b_month);
  }

  # Checking for the months with 30 days.
  elsif ($b_month =~ /^(0?[469]|11)$/ && $b_day > 30) {
    print "Sorry, $month_name only has 30 days.\n";
    $b_day = birth_day($b_year,$b_month);
  }

  return $b_day;
}

# Let's personalize it a bit. :)
print "What's your name? ";
chomp(my $name = <>);

my $birth_year = birth_year();
my $birth_month = birth_month();
my $birth_day = birth_day($birth_year,$birth_month);

my $year = (localtime)[5] + 1900;
my $month = (localtime)[4] + 1;
my $day = (localtime)[3];

# The following counts how many birthdays there has been.
# It also figures out the next year for a birthday.
# I'm still working on the kinks in the next birthday.
my $birthdays;
my $next_year;
if ($birth_month > $month) {
  $birthdays = $year - $birth_year - 1;
  $next_year = $year;
}
else {
  if ($birth_day > $day) {
    $birthdays = $year - $birth_year - 1;
    $next_year = $year;
  }
  else {
    $birthdays = $year - $birth_year;
    $next_year = $year + 1;
  }
}

my @birth = ($birth_year,$birth_month,$birth_day);
my @next_bday = ($next_year,$birth_month,$birth_day);
my @today = ($year,$month,$day);

my $days_alive = Delta_Days(@birth,@today);
my $days_til_next_bday = Delta_Days(@today,@next_bday);
my $unbirthdays = ORD(commify($days_alive - $birthdays));

print "\nHappy $unbirthdays unbirthday, $name!\n";
print "You have $days_til_next_bday days until your next birthday.\n";