import { describe, expect, it } from "vitest";
import { readSources } from "./rawSources.testkit";

// Every infinite list's read-ahead waits while the list fetches ANYTHING and runs again when the fetch
// settles. A read-ahead that only checks `isFetchingNextPage` calls during a background
// refetch, joins it through NEXT_PAGE and loads no page: the grid stalls at its loaded end until the
// reader scrolls the range. The jsdom virtualizer measures nothing, so the wiring is pinned in source.
const files = readSources(__dirname, ["../**/*.tsx", "!../**/*.test.tsx", "!../design-lab/**"]);
const source = (name: string) => {
  const hit = Object.entries(files).find(([path]) => path.endsWith(`/${name}`));
  if (!hit) throw new Error(`no ${name}`);
  return hit[1] as string;
};

describe("an infinite list's read-ahead", () => {
  it.each(["ui/VirtualGrid.tsx", "PlexBrowse.tsx"])(
    "%s gates on mayReadAhead and re-runs on isFetching",
    (file) => {
      const src = source(file);
      expect(src).toMatch(/mayReadAhead\(hasNextPage, isFetching\)/);
      expect(src).toMatch(/\[[^\]]*\bisFetching\b[^\]]*fetchNextPage\]\);/);
      expect(src).not.toMatch(/hasNextPage && !isFetchingNextPage/);
    },
  );

  it("the feed hands the grid the query's isFetching", () => {
    expect(source("Feed.tsx")).toMatch(/isFetching=\{query\.isFetching\}/);
  });

  // Retry is off, so a failed page settles at once; a read-ahead that re-runs on the settle would
  // request it again once a round-trip while the end is in view.
  it("stands down at a failed next page", () => {
    expect(source("Feed.tsx")).toMatch(
      /hasNextPage=\{!!hasNextPage && !query\.isFetchNextPageError\}/,
    );
    expect(source("PlexBrowse.tsx")).toMatch(
      /const hasNextPage = browseQ\.hasNextPage && !isFetchNextPageError;/,
    );
  });
});

// A click joins an in-flight next page but cancels a background refetch (nextPageOnClick): through
// NEXT_PAGE it would join the refetch and load nothing. NEXT_PAGE is only for the read-aheads, so a
// click site that goes back to it fails here (the YouTube "Load more" was once missed).
describe("a click that loads the next page", () => {
  const READ_AHEADS = new Set(["components/ui/VirtualGrid.tsx", "modules/plex/PlexBrowse.tsx"]);
  it("uses nextPageOnClick; NEXT_PAGE only in the read-aheads", () => {
    const users = Object.entries(files)
      .filter(([, src]) => /fetchNextPage\(NEXT_PAGE\)/.test(src as string))
      .map(([path]) => path.replace(/^\.\.\//, ""));
    expect(users.sort()).toEqual([...READ_AHEADS].sort());
    for (const [file, sites] of [
      ["AdminLogs.tsx", 2],
      ["Feed.tsx", 2],
      ["PlexBrowse.tsx", 1],
    ] as const)
      expect(source(file).match(/fetchNextPage\(nextPageOnClick\(/g)?.length, file).toBe(sites);
  });
});