use warnings;
use strict;
use Graph;

my $data = {
          '986172' => {
                        'cat_parent_id' => '',
                        'cat_name' => 'Category1'
                      },
          '986178' => {
                        'cat_parent_id' => '986177',
                        'cat_name' => 'Category4'
                      },
          '986177' => {
                        'cat_parent_id' => '986176',
                        'cat_name' => 'Category3'
                      },
          '986176' => {
                        'cat_name' => 'Category2',
                        'cat_parent_id' => '986172'
                      }
        };

my $g = Graph->new(directed => 1);
for my $k (keys %$data) {
	next unless $data->{$k}{cat_parent_id};
	die unless exists $data->{ $data->{$k}{cat_parent_id} };
	$g->add_edge($data->{$k}{cat_parent_id}, $k);
}
my $string = join ",", map { $data->{$_}{cat_name} }
	$g->topological_sort;