#!/usr/bin/perl

use strict;
use warnings;

use Digest::MD5 qw( md5_hex );
use List::Util  qw( max );

my $participants_qfn = 'santaList.txt'; # Name#email
my $previous_qfn     = 'lastYear.txt';  # sorted md5 hashes

my @participants = do { open(my $fh, '<', $participants_qfn)
                           or die $!;
                        map { /^(.*?)#/ ? $1 : () } <$fh>
                      };

my %previous = do { open(my $fh, '<', $previous_qfn)
                       or die $!;
                    map { /^(.*)/ ? $1 => 1 : () } <$fh>
                  };

my $longest = max map length, @participants;

my %givers  = map { $_ => 1 } @participants;
my %recvers = map { $_ => 1 } @participants;

my %gives_to;

for my $giver (@participants) {
   while ( my ($recver) = each %recvers ) {
      next if $giver eq $recver;

      my $hash = md5_hex($giver, '=>', $gives_to{$recver});
      next if !$previous{$hash};

      $gives_to{$giver} = $recver;
      delete $givers{$giver};
      delete $recvers{$recver};
      last;
   }
   keys %to;  # Reset iterator.
}

{
   my $fmt = "%-${longest}s => %s\n";
   print("Matched\n");
   print("=======\n");
   printf($fmt, $_, $gives_to{$_}) for sort keys %gives_to;

   print("Unmatched Givers\n");
   print("================\n");
   print("$_\n") for sort keys %givers;

   print("Unmatched Receivers\n");
   print("===================\n");
   print("$_\n") for sort keys %recvers;
}