/**
 * Pro auth for the AI proxy.
 *
 * When the proxy's Pro gate is enabled (`SASQUATCH_REQUIRE_PRO=1`) every
 * `/api/ai` request must carry:
 *   • `x-sasquatch-auth` — a base64 NIP-98 (kind 27235) event proving the caller;
 *   • `x-sasquatch-pro`  — base64 of the Pro zap receipt proving an active pass.
 *
 * The NIP-98 event is signed ONCE per session and reused, so an interactive
 * signer (Amber) doesn't pop on every message.
 */
import type { NostrEvent } from '@nostrify/nostrify';

type SignEvent = (event: {
  kind: number;
  created_at: number;
  tags: string[][];
  content: string;
}) => Promise<NostrEvent>;

let cachedAuthHeader: string | null = null;
let cachedAuthPubkey: string | null = null;

function toBase64(value: string): string {
  // Event JSON is ASCII (hex pubkeys/ids, tags), so btoa is safe here.
  return btoa(value);
}

export async function buildProAuthHeaders(opts: {
  pubkey?: string;
  signEvent?: SignEvent;
  receiptEvent?: NostrEvent | null;
}): Promise<Record<string, string>> {
  const { pubkey, signEvent, receiptEvent } = opts;
  const headers: Record<string, string> = {};
  if (!pubkey || !signEvent) return headers;

  if (cachedAuthPubkey !== pubkey || !cachedAuthHeader) {
    const event = await signEvent({
      kind: 27235,
      created_at: Math.floor(Date.now() / 1000),
      tags: [
        ['u', 'https://skate-spots.org/api/ai'],
        ['method', 'POST'],
      ],
      content: '',
    });
    cachedAuthHeader = toBase64(JSON.stringify(event));
    cachedAuthPubkey = pubkey;
  }

  headers['x-sasquatch-auth'] = cachedAuthHeader;
  if (receiptEvent) headers['x-sasquatch-pro'] = toBase64(JSON.stringify(receiptEvent));
  return headers;
}