import fs from "node:fs";
import path from "node:path";
import type {
  HomepageSummary,
  HomepageSummarySite,
} from "yt-dlp-transcript-common/lib/homepageSummary";
import { wordmarkLeadFor } from "yt-dlp-transcript-common/lib/brand";

// The build-time cross-site summary, or null when this build shipped without
// corpus data (`build:nodata`, or a source-only checkout that has never run
// compose — see next.config.ts).
//
// NULL, NOT AN EMPTY SUMMARY. The previous loader synthesized a zero-filled
// summary so the page always had something to render, which turned "we have no
// data" into "0 transcripts · 0 sites" — a claim that the product does nothing,
// printed in the same typeface as the real numbers. Callers must branch: render
// the live numbers only when this returns non-null, and say plainly why they're
// absent otherwise.
//
// Read with `readFileSync` at module scope of a server component, mirroring
// export/app/changelog/page.tsx. `output: "export"` means this runs at build,
// never at request time.
export function loadSummary(): HomepageSummary | null {
  try {
    const file = summaryFile(
      process.env,
      path.join(/* turbopackIgnore: true */ process.cwd(), "public", "homepage-summary.json"),
    );
    const parsed = JSON.parse(
      fs.readFileSync(/* turbopackIgnore: true */ file, "utf8"),
    ) as HomepageSummary;
    // A file that exists but carries no sites/totals is as uninformative as no
    // file at all; treat it the same rather than rendering an empty dashboard.
    if (!parsed || typeof parsed.totals?.transcripts !== "number") return null;
    return { ...parsed, sites: (parsed.sites ?? []).map(withCheckedLead) };
  } catch {
    return null;
  }
}

// The file loadSummary reads: `public/homepage-summary.json`, or the file
// E2E_HOMEPAGE_SUMMARY_FILE names — but ONLY outside a production build. The e2e's
// `next dev` points it at a synthetic summary (e2e/fixture-summary.ts, written
// by playwright.config.ts);
// `next build` runs with NODE_ENV=production and ignores it, so a variable left
// in a build shell can never ship a fixture as the homepage's numbers.
export function summaryFile(
  env: Readonly<Record<string, string | undefined>>,
  publicFile: string,
): string {
  const override = env.NODE_ENV !== "production" ? env.E2E_HOMEPAGE_SUMMARY_FILE : undefined;
  return override || publicFile;
}

// A site's `wordmarkLead` (release 14) is used only when it is what compose
// would have written: a proper prefix of its title (lib/brand.ts
// wordmarkLeadFor). A summary from before release 14 has none, and one edited
// by hand may hold anything; either way the card then shows the plain title.
export function withCheckedLead(site: HomepageSummarySite): HomepageSummarySite {
  const { wordmarkLead, ...rest } = site;
  const lead = wordmarkLeadFor(site.siteTitle, wordmarkLead);
  return lead ? { ...rest, wordmarkLead: lead } : rest;
}