#! perl
use strict;
use warnings;
use String::LCSS;

use constant {
                 CASE_SENSITIVE  =>  0,
                 DICTIONARY_FILE => 'words.txt',
             };

print 'Enter the target word:    ';
chomp(my $orig_target = <STDIN>);
my $target = CASE_SENSITIVE ? $orig_target : lc $orig_target;

open(my $in, '<', DICTIONARY_FILE)
    or die "Cannot open file '" . DICTIONARY_FILE . "' for reading: $!";
my %substrings;

while (my $orig_word = <$in>)
{
    chomp $orig_word;
    my $word = CASE_SENSITIVE ? $orig_word : lc $orig_word;
    my @lcss = lcss($word, $target);
    $substrings{ $lcss[0] } = [ $orig_word, $lcss[1], $lcss[2] ] if $lcss[0];
}

close $in
    or die "Cannot close file '" . DICTIONARY_FILE . "': $!";

print 'Target:                   ', $orig_target, "\n";

if (%substrings)
{
    my $key    = (sort { length $a <=> length $b } keys %substrings)[-1];
    my $match  =  $substrings{ $key }->[0];
    my $index2 =  $substrings{ $key }->[2];
    my $substr =  substr($orig_target, $index2, length $key);

    print 'Closest match:            ', $match,  "\n";
    print 'Longest common substring: ', $substr, "\n";
}
else
{
    print "No matches found\n";
}

sub lcss
{
    my ($first, $second) = @_;

    $first  .= '$';     # force strings to be different:
    $second .= '@';     #   kludge required by String::LCSS::lcss

    my @results = String::LCSS::lcss($first, $second);

    return wantarray ? @results : $results[0];
}