/**
 * Page-based pagination: reading `page` and `limit` from a query string, and
 * cutting fetched rows into a page.
 *
 * @module
 */

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

/**
 * Reads the `page` and `limit` query parameters. `page` is at least 1 and
 * defaults to 1; `limit` is clamped to [1, {@link PAGINATION_MAX_LIMIT}] and
 * defaults to `defaultLimit`.
 */
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 };
}

/** One page of a list, and whether another follows. */
export interface Page<T> {
  /** The page's items, in order. */
  items: T[];
  /** Whether another page follows this one. */
  hasMore: boolean;
}

/**
 * Turns rows fetched with `LIMIT limit + 1` into a page: the extra row, if it
 * came back, is dropped and says there's a next page. No COUNT(*) over the
 * whole list just to know that.
 */
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 };
}