use strict;
use warnings;
use diagnostics;
use File::Basename;                         # basename
use File::Spec::Functions;                  # catdir
use Data::Dumper;                           # Dumper
use Data::Dump;                             # dd
use constant DD => 1;                       # 0 = none, 1 = Dumper, 2 = Dump

my $data = data_for_path('./test');         # '/root/excerise_perl/test'

print "RESULT:\n";
DD == 2 ? dd $data : print Dumper($data);   # default to Data::Dumper

sub data_for_path
{
    my ($path) = @_;
    my  $data  = {};
    my  @queue = ( [ $path, $data ] );
    my  $count = 0;

    show_queue($count, \@queue) if DD;

    while (my $next = shift @queue)
    {
        if (DD)
        {
            print "($count) \$next:\n";
            DD == 2 ? dd $next : print Dumper($next);
            print '=' x 50, "\n";
        }

        my ($path, $ref) = @$next;
        my  $basename    = basename($path);

        $ref->{$basename} = do
        {
            if (-f $path or -l $path)   # plain file or symbolic link
            {
                undef;
            }
            else
            {
                my $hash = {};
                opendir((my $dh), $path);
                my @new_paths = map  { catfile $path , $_ }
                                grep { !/^\.\.?\z/ } readdir $dh;

                unshift @queue, map { [$_, $hash] } @new_paths;
                $hash;
            }
        };
    }
    continue
    {
        show_queue(++$count, \@queue) if DD;
    }

    $data;
}

sub show_queue
{
    my ($count, $queue) = @_;

    print "($count) \@queue:\n";
    DD == 2 ? dd $queue : print Dumper($queue);
    print '-' x 50, "\n";
}