import { createHash } from 'node:crypto';
import { verifyEvent, type Event } from 'nostr-tools/pure';

export const NIP98_KIND = 27235;

export class Nip98Error extends Error {}

export interface Nip98Options {
  /** Full URLs the signed `u` tag is allowed to match (same request via different hosts). */
  allowedUrls: string[];
  method: string;
  body?: Buffer | null;
  maxSkewSecs: number;
  now?: number;
  /** Returns true if the event id was already used (replay). */
  isReplay?: (eventId: string) => boolean;
}

function tag(event: Event, name: string): string | undefined {
  return event.tags.find((t) => t[0] === name)?.[1];
}

function normalizeUrl(u: string): string {
  try {
    const url = new URL(u);
    return `${url.protocol}//${url.host}${url.pathname.replace(/\/+$/, '') || '/'}${url.search}`;
  } catch {
    return u;
  }
}

/** Verify a NIP-98 `Authorization: Nostr <base64 event>` header. Returns the signer pubkey. */
export function verifyNip98(header: string | undefined, opts: Nip98Options): string {
  if (!header?.startsWith('Nostr ')) throw new Nip98Error('missing Nostr authorization header');

  let event: Event;
  try {
    event = JSON.parse(Buffer.from(header.slice(6).trim(), 'base64').toString('utf8'));
  } catch {
    throw new Nip98Error('malformed authorization event');
  }

  if (event.kind !== NIP98_KIND) throw new Nip98Error(`wrong event kind (expected ${NIP98_KIND})`);

  const now = opts.now ?? Math.floor(Date.now() / 1000);
  if (Math.abs(now - event.created_at) > opts.maxSkewSecs) {
    throw new Nip98Error('authorization event expired or clock skew too large — check your clock');
  }

  const u = tag(event, 'u');
  if (!u || !opts.allowedUrls.some((a) => normalizeUrl(a) === normalizeUrl(u))) {
    throw new Nip98Error('u tag does not match the request URL');
  }

  const method = tag(event, 'method');
  if (!method || method.toUpperCase() !== opts.method.toUpperCase()) {
    throw new Nip98Error('method tag does not match the request method');
  }

  if (opts.body && opts.body.length > 0) {
    const payload = tag(event, 'payload');
    const digest = createHash('sha256').update(opts.body).digest('hex');
    if (payload && payload !== digest) throw new Nip98Error('payload hash mismatch');
  }

  if (!verifyEvent(event)) throw new Nip98Error('invalid event signature');

  if (opts.isReplay?.(event.id)) throw new Nip98Error('authorization event already used');

  return event.pubkey;
}