function nae_get_dataset (){
    $args = array(
        'posts_per_page' => -1,
        'post_type'        => 'post',
        'post_status'      => 'publish'
    );
    $post_array = get_posts( $args );
    $nodes = [];
    $edges = [];

    foreach ($post_array as $post) {
        $category = get_the_category($post->ID);
        $root_category_ID = array_pop(get_ancestors( $category[0]->cat_ID, 'category' ));
        $root_category = get_category($root_category_ID);

        $nodes[] = [
            'id' => $post->ID,
            'label' => $post->post_name,
            'group' => $root_category->slug,
            'title' => '<a href="'.get_permalink($post).'" target="_blank">'.$post->post_title.'</a>'
        ];
        $html = do_shortcode($post->post_content);
        $dom = new DOMDocument; 
        @$dom->loadHTML(mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8'));
        $xpath = new DOMXPath($dom);

        $query = "//a[
            @href != ''
            and not(starts-with(@href, '#'))
            and normalize-space() != ''
        ]";

        foreach ($xpath->query($query) as $node) {
            $href = $xpath->evaluate('string(@href)', $node);
            $linked_post_id = url_to_postid($href);
            if ($linked_post_id != 0) {
                $edges[] = [
                    'from' => $post->ID,
                    'to' => $linked_post_id
                ];
            }
        }
    }
    return "[".json_encode($nodes).",".json_encode($edges)."]";
}

function nae_echo_article_map(){
    $dataset = nae_get_dataset ();
    $body = <<<EOD
    <div id="mynetwork" style="width: 100%; height: 800px; border: 1px solid lightgray;"></div>
    <div>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/vis/4.20.0/vis.min.js"></script>
    <link href="https://cdnjs.cloudflare.com/ajax/libs/vis/4.20.0/vis.min.css" rel="stylesheet">
    <script type="text/javascript">
        var dataset = $dataset;
        var nodedata = dataset[0];
        var edgedata = dataset[1];
        // create an array with nodes
        var nodes = new vis.DataSet(nodedata);
        // create an array with edges
        var edges = new vis.DataSet(edgedata);
        // create a network
        var container = document.getElementById('mynetwork');
        // provide the data in the vis format
        data = {  nodes: nodes, edges: edges };
        var options = {
            edges:{
                arrows: {
                      to:     {enabled: true, scaleFactor:1, type:'arrow'}
                }
             }
         };
        // initialize your network!
        var network = new vis.Network(container, data, options);
        // double click node to open an article
        network.on('doubleClick', function(e){
            var nodeID = e.nodes.toString();
            var url = jQuery(data.nodes.get(nodeID)['title']).attr('href');
            console.log(jQuery(data.nodes.get(nodeID)['title'])); console.log(url); 
            window.open(url,'_blank');
        });
    </script>
    </div>
EOD;
    return $body;
}

add_shortcode( 'show_article_map', 'nae_echo_article_map' );