// Browser-side reader for the same-origin GET /api/feed route.

export interface FeedPage {
  items: unknown[];
  nextCursor: string | null;
}

export class FeedLoadError extends Error {
  constructor(public readonly signedOut: boolean) {
    super(signedOut ? "sign_in" : "feed_unavailable");
  }
}

export async function fetchFeedPage(
  cursor: string | null,
  fetchImpl: typeof fetch = fetch,
): Promise<FeedPage> {
  const qs = new URLSearchParams({ limit: "20" });
  if (cursor) qs.set("cursor", cursor);
  let res: Response;
  try {
    res = await fetchImpl(`/api/feed?${qs.toString()}`, { credentials: "same-origin" });
  } catch {
    throw new FeedLoadError(false);
  }
  if (res.status === 401) throw new FeedLoadError(true);
  if (!res.ok) throw new FeedLoadError(false);
  try {
    const body = (await res.json()) as { items?: unknown; nextCursor?: unknown };
    return {
      items: Array.isArray(body.items) ? body.items : [],
      nextCursor: typeof body.nextCursor === "string" && body.nextCursor ? body.nextCursor : null,
    };
  } catch {
    throw new FeedLoadError(false);
  }
}