/**
 * Reads the page a list route's query string asks for, and cuts the rows a
 * service fetched into that page. The routes send the page as
 * `PaginatedData`.
 *
 * @module
 */

import { PAGINATION_DEFAULT_LIMIT, PAGINATION_MAX_LIMIT } from "../config.ts";

/**
 * Reads the `page` and `limit` query parameters of a list route. It never
 * fails: a missing or invalid `page` reads as 1, and `limit` is kept between 1
 * and {@link PAGINATION_MAX_LIMIT}.
 */
export function parsePagination(
  params: URLSearchParams,
  defaultLimit = PAGINATION_DEFAULT_LIMIT,
): { page: number; limit: number } {
  const page = Math.max(
    1,
    parseInt(params.get("page") ?? "1") || 1,
  );
  const limit = Math.min(
    Math.max(
      1,
      parseInt(params.get("limit") ?? String(defaultLimit)) || defaultLimit,
    ),
    PAGINATION_MAX_LIMIT,
  );
  return { page, limit };
}

/**
 * Returned to the routes by the services' list functions, and sent as
 * `PaginatedData`.
 */
export interface Page<T> {
  items: T[];
  hasMore: boolean;
}

/**
 * Turns rows fetched with `LIMIT limit + 1` into a page. The extra row, when it
 * comes back, is dropped and tells that another page follows, which spares a
 * COUNT(*) over the whole list.
 */
export function pageOf<T>(rows: T[], limit: number): Page<T> {
  return rows.length > limit
    ? { items: rows.slice(0, limit), hasMore: true }
    : { items: rows, hasMore: false };
}