/**
 * Single source of truth for the backend URL used by Next.js server
 * components. Defaults to localhost in development; throws at *request time*
 * in production if BACKEND_URL isn't set so a misdeployed container fails
 * with a clear message instead of silently pointing at localhost. The check
 * is lazy so Next.js build-time page-data collection doesn't trip it.
 */

let warned = false;

export function getBackendUrl(): string {
  const explicit = process.env.BACKEND_URL;
  if (explicit) return explicit;
  if (process.env.NODE_ENV === "production") {
    throw new Error(
      "BACKEND_URL env var is required in production. " +
      "Set it to the backend service URL (e.g. http://backend:3001).",
    );
  }
  if (!warned) {
    warned = true;
    console.warn("[lib/api] BACKEND_URL unset — defaulting to http://localhost:3001 (dev only)");
  }
  return "http://localhost:3001";
}

/**
 * Fetch JSON from the backend with a default revalidate window. Returns
 * `null` on network failure or non-2xx status — callers handle the null
 * to render a graceful fallback instead of crashing the server render.
 */
export async function apiFetch<T>(
  path: string,
  options: { revalidate?: number } = {},
): Promise<T | null> {
  const { revalidate = 60 } = options;
  try {
    const res = await fetch(`${getBackendUrl()}${path}`, {
      next: { revalidate },
    });
    if (!res.ok) return null;
    return (await res.json()) as T;
  } catch {
    return null;
  }
}