interface PagerManagerInterface

interface PagerManagerInterface {
    
    /**
     * Initializes a pager.
     *
     * This function sets up the necessary variables so that the render system
     * will correctly process #type 'pager' render arrays to output pagers that
     * correspond to the items being displayed.
     *
     * If the items being displayed result from a database query performed using
     * Drupal's database API, and if you have control over the construction of the
     * database query, you do not need to call this function directly; instead,
     * you can extend the query object with the 'PagerSelectExtender' extender
     * before executing it. For example:
     * @code
     *   $query = db_select('some_table')
     *     ->extend('Drupal\Core\Database\Query\PagerSelectExtender');
     * @endcode
     *
     * However, if you are using a different method for generating the items to be
     * paged through, then you should call this service in preparation.
     *
     * The following example shows how this service can be used in a controller
     * that invokes an external datastore with an SQL-like syntax:
     * @code
     *   // First find the total number of items and initialize the pager.
     *   $total = mymodule_select("SELECT COUNT(*) FROM data WHERE status = 1")->result();
     *   $num_per_page = \Drupal::config('mymodule.settings')->get('num_per_page');
     *   $pager = \Drupal::service('pager.manager')->createPager($total, $num_per_page);
     *   $page = $pager->getCurrentPage();
     *
     *   // Next, retrieve the items for the current page and put them into a
     *   // render array.
     *   $offset = $num_per_page * $page;
     *   $result = mymodule_select("SELECT * FROM data " . $where . " LIMIT %d, %d", $offset, $num_per_page)->fetchAll();
     *   $render = [];
     *   $render[] = [
     *     '#theme' => 'mymodule_results',
     *     '#result' => $result,
     *   ];
     *
     *   // Finally, add the pager to the render array, and return.
     *   $render[] = ['#type' => 'pager'];
     *   return $render;
     * @endcode
     *
     * A second example involves a controller that invokes an external search
     * service where the total number of matching results is provided as part of
     * the returned set (so that we do not need a separate query in order to
     * obtain this information). Here, we call PagerManagerInterface->findPage()
     * to calculate the desired offset before the search is invoked:
     * @code
     *
     *   // Perform the query, using the requested offset from
     *   // PagerManagerInterface::findPage(). This comes from a URL parameter, so
     *   // here we are assuming that the URL parameter corresponds to an actual
     *   // page of results that will exist within the set.
     *   $pager_parameters = \Drupal::service('pager.parameters');
     *   $page = $pager_parameters->findPage();
     *   $num_per_page = \Drupal::config('mymodule.settings')->get('num_per_page');
     *   $offset = $num_per_page * $page;
     *   $result = mymodule_remote_search($keywords, $offset, $num_per_page);
     *
     *   // Now that we have the total number of results, initialize the pager.
     *   $pager_manager = \Drupal::service('pager.manager');
     *   $pager_manager->createPager($result->total, $num_per_page);
     *
     *   // Create a render array with the search results.
     *   $render = [];
     *   $render[] = [
     *     '#theme' => 'search_results',
     *     '#results' => $result->data,
     *     '#type' => 'remote',
     *   ];
     *
     *   // Finally, add the pager to the render array, and return.
     *   $render[] = ['#type' => 'pager'];
     *   return $render;
     * @endcode
     *
     * @param int $total
     *   The total number of items to be paged.
     * @param int $limit
     *   The number of items the calling code will display per page.
     * @param int $element
     *   (optional) An integer to distinguish between multiple pagers on one page.
     *
     * @return \Drupal\Core\Pager\Pager
     *   The pager.
     */
    public function createPager($total, $limit, $element = 0);
    
    /**
     * Gets a pager from the static cache.
     *
     * @param int $element
     *   The pager element index.
     *
     * @return \Drupal\Core\Pager\Pager|null
     *   The pager, or null if not found.
     */
    public function getPager($element = 0);
    
    /**
     * Gets the URL query parameter array of a pager link.
     *
     * Adds to or adjusts the 'page' URL query parameter so that if you follow the
     * link, you'll get page $index for pager $element on the page.
     *
     * The 'page' URL query parameter is a comma-delimited string, where each
     * value is the target content page for the corresponding pager $element. For
     * instance, if we have 5 pagers on a single page, and we want to have a link
     * to a page that should display the 6th content page for the 3rd pager, and
     * the 1st content page for all the other pagers, then the URL query will look
     * like this: ?page=0,0,5,0,0 (page numbering starts at zero).
     *
     * @param array $query
     *   An associative array of URL query parameters to add to.
     * @param int $element
     *   An integer to distinguish between multiple pagers on one page.
     * @param int $index
     *   The index of the target page, for the given element, in the pager array.
     *
     * @return array
     *   The altered $query parameter array.
     */
    public function getUpdatedParameters(array $query, $element, $index);

}