import fs from "node:fs";
import path from "node:path";

// Facts about the published source snapshot, written by `archilyzer source
// publish` (common/publish/source.ts) beside the tarball it describes. Since
// release 12 the tarball is `git archive` of the scrubbed MIRROR's main, so
// `commit` is a mirror id — the /source/ page names the private main it
// reflects.
export type Snapshot = {
  generatedAt: string;
  commit: string;
  subject: string;
  bytes: number;
  sha256: string;
};

// The tarball's public path. Stable by design: a dated filename would invalidate
// every link that has ever been shared the moment a new snapshot ships. The date
// lives in the sidecar instead.
export const SNAPSHOT_HREF = "/downloads/archilyzer-source.tar.gz";

// Read the sidecar, or null when this build has no snapshot.
//
// The null case is not hypothetical: the tarball and its sidecar are gitignored
// build artefacts, so a fresh unpack of the source has neither until
// `archilyzer source publish` runs (`archilyzer build homepage` runs it). The download page MUST render no link at all in
// that case — a link to a file that isn't there is worse than an explanation of
// why there isn't one.
export function loadSnapshot(): Snapshot | null {
  try {
    const file = path.join(
      /* turbopackIgnore: true */ process.cwd(),
      "public",
      "downloads",
      "snapshot.json",
    );
    const parsed = JSON.parse(fs.readFileSync(/* turbopackIgnore: true */ file, "utf8")) as Snapshot;
    if (!parsed || typeof parsed.bytes !== "number" || !parsed.sha256) {
      return null;
    }
    // Believe the sidecar only if the file it describes is actually present —
    // they are written together but deployed as separate assets.
    const tarball = path.join(
      /* turbopackIgnore: true */ process.cwd(),
      "public",
      "downloads",
      path.basename(SNAPSHOT_HREF),
    );
    if (!fs.statSync(/* turbopackIgnore: true */ tarball).isFile()) return null;
    return parsed;
  } catch {
    return null;
  }
}

export function formatBytes(bytes: number): string {
  const mb = bytes / (1024 * 1024);
  if (mb >= 1) return `${mb.toFixed(2)} MB`;
  return `${Math.round(bytes / 1024)} KB`;
}