class PagerPluginBase

abstract class PagerPluginBase extends PluginBase {
    public $current_page = NULL;
    public $total_items = 0;
    
    /**
     * {@inheritdoc}
     */
    protected $usesOptions = TRUE;
    
    /**
     * Get how many items per page this pager will display.
     *
     * All but the leanest pagers should probably return a value here, so
     * most pagers will not need to override this method.
     */
    public function getItemsPerPage() {
        return $this->options['items_per_page'] ?? 0;
    }
    
    /**
     * Set how many items per page this pager will display.
     *
     * This is mostly used for things that will override the value.
     */
    public function setItemsPerPage($items) {
        $this->options['items_per_page'] = $items;
    }
    
    /**
     * Get the page offset, or how many items to skip.
     *
     * Even pagers that don't actually page can skip items at the beginning,
     * so few pagers will need to override this method.
     */
    public function getOffset() {
        return $this->options['offset'] ?? 0;
    }
    
    /**
     * Set the page offset, or how many items to skip.
     */
    public function setOffset($offset) {
        $this->options['offset'] = $offset;
    }
    
    /**
     * Get the current page.
     *
     * If NULL, we do not know what the current page is.
     */
    public function getCurrentPage() {
        return $this->current_page;
    }
    
    /**
     * Set the current page.
     *
     * @param $number
     *   If provided, the page number will be set to this. If NOT provided,
     *   the page number will be set from the global page array.
     */
    public function setCurrentPage($number = NULL) {
        if (!is_numeric($number) || $number < 0) {
            $number = 0;
        }
        $this->current_page = $number;
    }
    
    /**
     * Get the total number of items.
     *
     * If NULL, we do not yet know what the total number of items are.
     */
    public function getTotalItems() {
        return $this->total_items;
    }
    
    /**
     * Get the pager id, if it exists.
     */
    public function getPagerId() {
        return $this->options['id'] ?? 0;
    }
    
    /**
     * Provide the default form for validating options.
     */
    public function validateOptionsForm(&$form, FormStateInterface $form_state) {
    }
    
    /**
     * Provide the default form for submitting options.
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
    }
    
    /**
     * Returns a string to display as the clickable title for the pager plugin.
     */
    public function summaryTitle() {
        return $this->t('Unknown');
    }
    
    /**
     * Determine if this pager actually uses a pager.
     *
     * Only a couple of very specific pagers will set this to false.
     */
    public function usePager() {
        return TRUE;
    }
    
    /**
     * Determine if a pager needs a count query.
     *
     * If a pager needs a count query, a simple query
     */
    public function useCountQuery() {
        return TRUE;
    }
    
    /**
     * Executes the count query.
     *
     * This will be done just prior to the query itself being executed.
     */
    public function executeCountQuery(&$count_query) {
        $this->total_items = $count_query->execute()
            ->fetchField();
        if (!empty($this->options['offset'])) {
            $this->total_items -= $this->options['offset'];
        }
        // Prevent from being negative.
        $this->total_items = max(0, $this->total_items);
        return $this->total_items;
    }
    
    /**
     * Updates the pager information.
     *
     * If there are pagers that need global values set, this method can
     * be used to set them. It will be called after the query is run.
     */
    public function updatePageInfo() {
    }
    
    /**
     * Modify the query for paging.
     *
     * This is called during the build phase and can directly modify the query.
     */
    public function query() {
    }
    
    /**
     * Perform any needed actions just prior to the query executing.
     */
    public function preExecute(&$query) {
    }
    
    /**
     * Perform any needed actions just after the query executing.
     */
    public function postExecute(&$result) {
    }
    
    /**
     * Perform any needed actions just before rendering.
     */
    public function preRender(&$result) {
    }
    
    /**
     * Return the renderable array of the pager.
     *
     * Called during the view render process.
     *
     * @param $input
     *   Any extra GET parameters that should be retained, such as exposed
     *   input.
     */
    public function render($input) {
    }
    
    /**
     * Determine if there are more records available.
     *
     * This is primarily used to control the display of a more link.
     */
    public function hasMoreRecords() {
        return $this->getItemsPerPage() && $this->total_items > (intval($this->current_page) + 1) * $this->getItemsPerPage();
    }
    public function exposedFormAlter(&$form, FormStateInterface $form_state) {
    }
    public function exposedFormValidate(&$form, FormStateInterface $form_state) {
    }
    public function exposedFormSubmit(&$form, FormStateInterface $form_state, &$exclude) {
    }
    public function usesExposed() {
        return FALSE;
    }
    protected function itemsPerPageExposed() {
        return FALSE;
    }
    protected function isOffsetExposed() {
        return FALSE;
    }

}