class PagerManager

class PagerManager implements PagerManagerInterface {
  use DependencySerializationTrait;

  /**
   * The pager parameters.
   *
   * @var \Drupal\Core\Pager\PagerParametersInterface
   */
  protected $pagerParams;

  /**
   * An associative array of pagers.
   *
   * Implemented as an array consisting of:
   *   - key: the element id integer.
   *   - value: a \Drupal\Core\Pager\Pager.
   *
   * @var array
   */
  protected $pagers;

  /**
   * The highest pager ID created so far.
   *
   * @var int
   */
  protected $maxPagerElementId = -1;

  /**
   * Construct a PagerManager object.
   *
   * @param \Drupal\Core\Pager\PagerParametersInterface $pager_params
   *   The pager parameters.
   */
  public function __construct(PagerParametersInterface $pager_params) {
    $this->pagerParams = $pager_params;
  }

  /**
   * {@inheritdoc}
   */
  public function createPager($total, $limit, $element = 0) {
    $currentPage = $this->pagerParams
      ->findPage($element);
    $pager = new Pager($total, $limit, $currentPage);
    $this
      ->setPager($pager, $element);
    return $pager;
  }

  /**
   * {@inheritdoc}
   */
  public function getPager($element = 0) {
    return $this->pagers[$element] ?? NULL;
  }

  /**
   * {@inheritdoc}
   */
  public function findPage(int $pager_id = 0) : int {
    return $this->pagerParams
      ->findPage($pager_id);
  }

  /**
   * {@inheritdoc}
   */
  public function getUpdatedParameters(array $query, $element, $index) {

    // Build the 'page' query parameter. This is built based on the current
    // page of each pager element (or NULL if the pager is not set), with the
    // exception of the requested page index for the current element.
    $element_pages = [];
    $max = $this
      ->getMaxPagerElementId();
    for ($i = 0; $i <= $max; $i++) {
      $currentPage = ($pager = $this
        ->getPager($i)) ? $pager
        ->getCurrentPage() : NULL;
      $element_pages[] = $i == $element ? $index : $currentPage;
    }
    $query['page'] = implode(',', $element_pages);

    // Merge the query parameters passed to this function with the parameters
    // from the current request. In case of collision, the parameters passed
    // into this function take precedence.
    if ($current_query = $this->pagerParams
      ->getQueryParameters()) {
      $query = array_merge($current_query, $query);
    }
    return $query;
  }

  /**
   * {@inheritdoc}
   */
  public function getMaxPagerElementId() {
    return $this->maxPagerElementId;
  }

  /**
   * {@inheritdoc}
   */
  public function reservePagerElementId(int $element) : void {
    $this->maxPagerElementId = max($element, $this->maxPagerElementId);
  }

  /**
   * Saves a pager to the static cache.
   *
   * @param \Drupal\Core\Pager\Pager $pager
   *   The pager.
   * @param int $element
   *   The pager index.
   */
  protected function setPager(Pager $pager, $element = 0) {
    $this->maxPagerElementId = max($element, $this->maxPagerElementId);
    $this->pagers[$element] = $pager;
  }

}