// Loading the swarm's display name from `GET /api/swarm`, once. The header and
// the start page both ask for it and it does not change within a page visit,
// so the loader remembers the first request and every caller shares it. The
// label is cosmetic, so a failed request, an error response or an unconfigured
// name all answer `null` instead of throwing: callers fall back to their own
// default, as an operator who never set a name sees.

type Fetch = (url: string) => Promise<{
  ok: boolean;
  json: () => Promise<unknown>;
}>;

export function createSwarmNameLoader(
  fetchImpl: Fetch,
): () => Promise<string | null> {
  let pending: Promise<string | null> | null = null;
  return () => {
    if (pending === null) {
      pending = (async () => {
        const r = await fetchImpl("/api/swarm");
        if (!r.ok) return null;
        const data = (await r.json()) as { name?: string | null };
        return data.name || null;
      })().catch(() => null);
    }
    return pending;
  };
}