router.php

<?php
/**
 * GS 'Routing' demonstration module
 *
 * Demonstrates how to use "data_index" to modify the page data
 * and how to use url segments to control process flows in your 
 * scripts.
 *
 * Required:
 * --------------------------------------------------------------
 *   RewriteEngine On
 *   RewriteCond %{REQUEST_FILENAME} !-f
 *   RewriteCond %{REQUEST_FILENAME} !-d
 *   RewriteRule ^(.*)$ index.php?id=$1 [L,QSA]
 */
register_plugin(
    'router',
    'Catalog Router',
    '0.1',
    'J.Ehret',
    'https://ehret-studio.com',
    'A simple router plugin',
    '',
    ''
);

/**
 * This is our gateway function, GetSimple calls this when "data_index" fired.
 * This is a good place to attach your code.
 */
add_filter('data_index',
    function($data)
    {
        $input = new \Input();
        /**
         * Break routing here if the page isn't a part of the catalog.
         * Just please remember to make the "last" segment as a slug,
         * so that GS would be able to use it in the native way:
         */
        if($input->urlSegments->get(0) != 'catalog') {
            global $pagesArray;
            $lastSegment =  $input->urlSegments->getLast();

            if(isset($pagesArray[$lastSegment])) {
                $data = getXml(GSDATAPAGESPATH . $lastSegment . '.xml');
            }
            return $data;
        }

        /**
         * From this point downwards all pages belongs to your catalog
         * and you can now use URL segments to control your process flow.
         *
         * URL segments can be accessed from the $input->urlSegments variable:
         *
         * $input->urlSegments->get($n)   // Retrieve the $n'th URL segment (1-...)
         *
         * $input->urlSegments->getLast() // Retrieve the last segment
         *
         * $input->urlSegments->total     // The total number of segments
         *
         * For example the URL could be:
         * 1) /catalog/
         * 2) /catalog/category/
         * 3) /catalog/category/subcategory/
         * 3) /catalog/category/subcategory/item/
         * 4) etc
         *
         * Lets assume that the path /catalog/food/fruits/bananas/
         *
         * $input->urlSegments->get(0) // catalog
         * $input->urlSegments->get(1) // food
         * $input->urlSegments->get(2) // fruits
         * $input->urlSegments->get(3) // bananas
         *
         */

        // Set default values
        $pageTitle = null;
        $metaTags  = null;
        $metaDescr = null;
        $menuLabel = null;
        $template = 'template.php';
        $url = 'slug-you-want-to-set';
        $content = 'This is the default content, could be 404 page';
        // ...

        // /catalog/category/subcategory/item/
        if($input->urlSegments->get(3))
        {
            $pageTitle = 'My Item Page Title';
            $metaTags  = 'my, item, tags, ...';
            $metaDescr = 'Meta item decr...';
            $menuLabel = 'Your Item Menu Label';
            $url = $input->urlSegments->get(3);
            //$template = 'your-item-template-file.php';

            $content = 'This is the Item page content '.$input->urlSegments->get(3);
            // Or function call: render_item_content($input->urlSegments->get(3));

        //	/catalog/category/subcategory/
        } elseif($input->urlSegments->get(2))
        {
            $pageTitle = 'My Subcat Page Title';
            $metaTags  = 'my, subcat, tags, ...';
            $metaDescr = 'Meta subcat decr...';
            $menuLabel = 'Your Subcategory Menu Label';
            //$template = 'your-subcategory-template-file.php';

            $content = 'This is the Subcategory page content';
            // Or function call: render_subcategory_content();

        // /catalog/category/
        } elseif($input->urlSegments->get(1))
        {
            $pageTitle = 'My Cat Page Title';
            $metaTags  = 'my, cat, tags, ...';
            $metaDescr = 'Meta cat decr...';
            $menuLabel = 'Your Subcategory Menu Label';
            //$template = 'your-category-template-file.php';

            $content = 'This is the Category page content';
            // Or function call: render_category_content();

        // /catalog/
        } elseif($input->urlSegments->get(0) == 'catalog')
        {
            $pageTitle = 'My Cat Page Title';
            $metaTags  = 'my, cat, tags, ...';
            $metaDescr = 'Meta cat decr...';
            $menuLabel = 'Your Subcategory Menu Label';
            //$template = 'your-category-template-file.php';

            $content = 'This is the Catalog page content';
            // Or function call: render_category_content();
        }


        $sxe = new \SimpleXMLExtended('<?xml version="1.0" encoding="UTF-8"?><item></item>');
        $sxe->addChild('pubDate', date('r'));
        $sxe->addChild('title', $pageTitle);
        $sxe->addChild('url', $url);
        $sxe->addChild('meta', $metaTags);
        $sxe->addChild('metad', $metaDescr);
        $sxe->addChild('menu', $menuLabel);
        $sxe->addChild('template', $template);
        $sxe->addChild('content', $content);
        // ...

        return $sxe;
    }
);

class Input
{
    public $urlSegments;

    public function __construct() {
        $this->urlSegments = new \UrlSegments();
        $this->parseUrl();
    }

    private function parseUrl() {
        $currentPath = isset($_GET['id']) ? $_GET['id'] : 'index';
        $this->buildSegments($currentPath);
    }

    private function buildSegments($url) {
        $parseUrl = parse_url(trim($url));
        if(isset($parseUrl['path'])) {
            foreach(array_values(array_filter(array_map('trim', explode('/', $parseUrl['path'])))) as $key => $value) {
                $this->urlSegments->set($key, basename($value));
                $this->urlSegments->total++;
            }
        }
    }
}

class UrlSegments
{
    public $total = 0;

    public function set($id, $value) {
        $this->segment{$id} = $value;
    }

    public function get($id) {
        return isset($this->segment{$id}) ? $this->segment{$id} : null;
    }

    public function getLast() {
        return isset($this->segment{($this->total - 1)}) ? $this->segment{($this->total - 1)} : null;
    }
}