Grav as Headless CMS

<?php
namespace Grav\Plugin;

use Composer\Autoload\ClassLoader;
use Grav\Common\Plugin;

class PageAsDataPlugin extends Plugin {
  const api = '/api/';
  /** The url of page being called */
  protected $pageUrl;

  public static function getSubscribedEvents() {
    return [
      'onPluginsInitialized' => [
        ['onPluginsInitialized', 0]
      ],
    ];
  }

  public function onPluginsInitialized() {
    if ($this->isAdmin()) {
      return;
    }
    // Enable the main events we are interested in
    $lengthApi = strlen(self::api);
    $url = $this->grav['uri']->url();

    // If the API is being called
    if (substr($url, 0, strlen(self::api)) === self::api) {
      $this->pageUrl = substr($url, $lengthApi - 1);
      $this->enable([
        'onPageInitialized' => ['deliverFormatAs', 0]
      ]);
    }
  }

  /**
   * Delivers the page as a different format.
   */
  public function deliverFormatAs($event) {
    /**
     * @var \Grav\Common\Page\Page $page
     */
    $pages = $this->grav['pages'];
    $page = $pages->find($this->pageUrl);
    $collection = $page->collection('content');
    $pageArray = $page->toArray();
    $children = array();
    foreach ($collection as $item) {
      $children[] = $item->toArray();
    }
    $pageArray['children'] = $children;
    header("Content-Type: application/json");
    echo json_encode($pageArray);
    exit();
  }
}

/**
 * Converts an array to XML
 *  http://www.devexp.eu/2009/04/11/php-domdocument-convert-array-to-xml/
 */
/**
 * Extends the DOMDocument to implement personal (utility) methods.
 * - From: http://www.devexp.eu/2009/04/11/php-domdocument-convert-array-to-xml/
 * - parent:: See http://www.php.net/manual/en/class.domdocument.php
 *
 * @throws   DOMException   http://www.php.net/manual/en/class.domexception.php
 *
 * @author Toni Van de Voorde
 */
class PageAsDataXmlDomConstructor extends \DOMDocument {
  public function fromMixed($mixed, \DOMElement $domElement = null) {
    $domElement = is_null($domElement) ? $this : $domElement;
    if (is_array($mixed)) {
      foreach ($mixed as $index => $mixedElement) {
        if (is_int($index)) {
          if ($index == 0) {
            $node = $domElement;
          } else {
            $node = $this->createElement($domElement->tagName);
            $domElement->parentNode->appendChild($node);
          }
        } else {
          $node = $this->createElement($index);
          $domElement->appendChild($node);
        }
        $this->fromMixed($mixedElement, $node);
      }
    } else {
      $domElement->appendChild($this->createTextNode($mixed));
    }
  }
}

header("Content-Type: application/json");
echo json_encode($pageArray);