/**
 * Best-effort fetch of the relay host's /.well-known/ap2p descriptor so the
 * operator can rotate the relay's PeerId or TURN endpoint without a client
 * release. Baked-in defaults win when the fetch fails (static IPFS hosting
 * must keep working offline).
 */

export interface MailboxConfig {
  baseUrl: string;
  credsUrl: string;
  maxMessageKb: number;
}

export interface RelayConfig {
  relayMultiaddr: string;
  turnCredsUrl: string;
  discoveryTopic: string;
  /** Offline store-and-forward mailbox; absent ⇒ feature off (PROTOCOL.md §9). */
  mailbox?: MailboxConfig;
}

interface Ap2pDescriptor {
  relay?: { multiaddrs?: string[]; pubsub_discovery_topic?: string };
  endpoints?: { turn_credentials?: string };
  mailbox?: { endpoint?: string; mint_endpoint?: string; max_message_kb?: number };
}

export async function resolveRelayConfig(defaults: RelayConfig, timeoutMs = 2000): Promise<RelayConfig> {
  const host = defaults.relayMultiaddr.match(/^\/dns4\/([^/]+)\//)?.[1];
  if (!host) return defaults; // dev/self-host multiaddr (ip4 etc.) — no descriptor
  try {
    const res = await fetch(`https://${host}/.well-known/ap2p`, {
      signal: AbortSignal.timeout(timeoutMs),
    });
    if (!res.ok) return defaults;
    const d = (await res.json()) as Ap2pDescriptor;
    const mailbox: MailboxConfig | undefined =
      d.mailbox?.endpoint && d.mailbox?.mint_endpoint
        ? {
            baseUrl: d.mailbox.endpoint,
            credsUrl: d.mailbox.mint_endpoint,
            maxMessageKb: d.mailbox.max_message_kb ?? 64,
          }
        : defaults.mailbox;
    return {
      relayMultiaddr: d.relay?.multiaddrs?.[0] ?? defaults.relayMultiaddr,
      turnCredsUrl: d.endpoints?.turn_credentials ?? defaults.turnCredsUrl,
      discoveryTopic: d.relay?.pubsub_discovery_topic ?? defaults.discoveryTopic,
      ...(mailbox ? { mailbox } : {}),
    };
  } catch {
    return defaults;
  }
}