shlink-web-client/src/utils/helpers/pagination.ts

import { max, min, range } from 'ramda';
import { prettify } from './numbers';

const DELTA = 2;

export const ELLIPSIS = '...';

type Ellipsis = typeof ELLIPSIS;

export type NumberOrEllipsis = number | Ellipsis;

export const progressivePagination = (currentPage: number, pageCount: number): NumberOrEllipsis[] => {
  const pages: NumberOrEllipsis[] = range(
    max(DELTA, currentPage - DELTA),
    min(pageCount - 1, currentPage + DELTA) + 1,
  );

  if (currentPage - DELTA > DELTA) {
    pages.unshift(ELLIPSIS);
  }
  if (currentPage + DELTA < pageCount - 1) {
    pages.push(ELLIPSIS);
  }

  pages.unshift(1);
  pages.push(pageCount);

  return pages;
};

export const pageIsEllipsis = (pageNumber: NumberOrEllipsis): pageNumber is Ellipsis => pageNumber === ELLIPSIS;

export const prettifyPageNumber = (pageNumber: NumberOrEllipsis): string =>
  pageIsEllipsis(pageNumber) ? pageNumber : prettify(pageNumber);

export const keyForPage = (pageNumber: NumberOrEllipsis, index: number) => !pageIsEllipsis(pageNumber) ? `${pageNumber}` : `${pageNumber}_${index}`;