upei_roblib_reserves/src/Plugin/Block/ReserveBlock.php

<?php

namespace Drupal\upei_roblib_reserves\Plugin\Block;

use Drupal\Core\Block\BlockBase;

/**
 * Provides a Reserves Block base on Evergreen bookbags.
 *
 * @Block(
 *   id = "upei_roblib_reserves_block",
 *   admin_label = @Translation("Roblib Reserves Block"),
 *   category = @Translation("UPEI Roblib"),
 * )
 */
class ReserveBlock extends BlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    $html = $this->getReserves();
    if (empty($html)) {
      return '';
    }

    return [
      '#theme' => 'upei_roblib_reserves_block',
      '#atom_to_html' => [
        '#markup' => $html,
      ],
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function getCacheMaxAge() {
    //Reading dynamic content from external source so no caching.
    return 0;
  }

  /**
   * Queries Evergreen for an Atom XML feed based on book bag list.
   * 
   * @return string
   *   HTML created from Atom XML feed.
   */
  protected function getReserves() {
    $node = \Drupal::routeMatch()->getParameter('node');

    $html = '';
    if ($node && $node instanceof \Drupal\node\NodeInterface && $node->bundle() == 'course_reserve') {
      $book_bag_id = (string) $node->field_bookbag_id->value;
      if (empty($book_bag_id)) {
        return '';
      }
      //The evergreen ILS base URL.
      $book_bag_base_url = 'http://islandpines.roblib.upei.ca/opac/extras/feed/bookbag/atom-full/';
      try {
        $response = \Drupal::httpClient()->get($book_bag_base_url . $book_bag_id);
        $atom = (string) $response->getBody();
        if (empty($atom)) {
          return '';
        }
      }
      catch (RequestException $e) {
        return '';
      }
      $path = \Drupal::service('extension.list.module')->getPath('upei_roblib_reserves');
      $xslt = new \XSLTProcessor();
      $xsl = new \DOMDocument();
      $xsl->load($path . '/xsl/atom2html.xsl');
      $xslt->importStylesheet($xsl);
      $xml = new \DomDocument();
      $xml->loadXML($atom);
      $html = $xslt->transformToXML($xml);
    }
    return $html;
  }

}