#!/usr/bin/perl
use strict;
use warnings;
use 5.10.0;
use LWP::Simple;
use XML::Feed;
use XML::Simple;
use GraphViz::Data::Grapher;
use Readonly;

Readonly my $usage => "$0 <URI of page with feeds>";

die $usage unless($#ARGV==0);

my $page_url = $ARGV[0];
$page_url = "http://$page_url" unless ($page_url =~ /^https?:\/\//);  

my @feeds = XML::Feed->find_feeds($page_url);
my $i = 0;
for(@feeds) {
    my $xml = get($_);
    die "Couldn't fetch feed" unless defined $xml;
    my $feed = XMLin($xml);
    my $graph = GraphViz::Data::Grapher->new($feed);
    $graph->{LAYOUT}='fdp';
    $graph->{RATIO}=1.618;  # naturally
    print $graph->as_png("feed_structure-$i.png");
    $i++;
}