GridFieldOrderableRows::handleMoveToPage PHP Method

    public function handleMoveToPage(GridField $grid, $request)
    {
        if (!($paginator = $grid->getConfig()->getComponentByType('GridFieldPaginator'))) {
            $this->httpError(404, 'Paginator component not found');
        }
        $move = $request->postVar('move');
        $field = $this->getSortField();
        $list = $grid->getList();
        $manip = $grid->getManipulatedList();
        $existing = $manip->map('ID', $field)->toArray();
        $values = $existing;
        $order = array();
        $id = isset($move['id']) ? (int) $move['id'] : null;
        $to = isset($move['page']) ? $move['page'] : null;
        if (!isset($values[$id])) {
            $this->httpError(400, 'Invalid item ID');
        }
        $this->populateSortValues($list);
        $page = (int) $grid->getState()->GridFieldPaginator->currentPage ?: 1;
        $per = $paginator->getItemsPerPage();
        if ($to == 'prev') {
            $swap = $list->limit(1, ($page - 1) * $per - 1)->first();
            $values[$swap->ID] = $swap->{$field};
            $order[] = $id;
            $order[] = $swap->ID;
            foreach ($existing as $_id => $sort) {
                if ($id != $_id) {
                    $order[] = $_id;
                }
            }
        } elseif ($to == 'next') {
            $swap = $list->limit(1, $page * $per)->first();
            $values[$swap->ID] = $swap->{$field};
            foreach ($existing as $_id => $sort) {
                if ($id != $_id) {
                    $order[] = $_id;
                }
            }
            $order[] = $swap->ID;
            $order[] = $id;
        } else {
            $this->httpError(400, 'Invalid page target');
        }
        $this->reorderItems($list, $values, $order);
        return $grid->FieldHolder();
    }