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, $this->maxPagerElementId);
        // BC for PagerSelectExtender::$maxElement.
        // @todo remove the line below in D10.
        PagerSelectExtender::$maxElement = $this->getMaxPagerElementId();
    }
    
    /**
     * 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;
    }

}