/**
 * NIP-49 — password-encrypted private keys (`ncryptsec1…`)
 * ─────────────────────────────────────────────────────────────────────────────
 * A raw `nsec` in a text file is the worst artefact to hand a new user. NIP-49
 * wraps the key with scrypt + XChaCha20-Poly1305 under a password, so the blob
 * is safe to store in cloud storage, email, or a password manager — and it's a
 * portable login credential in its own right.
 *
 * Thin wrapper around `nostr-tools/nip49` (verified: round-trips, and a wrong
 * password is rejected by the AEAD, not by luck).
 */

import * as nip49 from 'nostr-tools/nip49';
import { nip19 } from 'nostr-tools';

export const NCRYPTSEC_PREFIX = 'ncryptsec1';

/** scrypt work factor. 16 ≈ 2^16 rounds — the usual NIP-49 default. */
const LOG_N = 16;

/** Encrypt a bech32 `nsec` into a password-protected `ncryptsec`. */
export function encryptNsec(nsec: string, password: string): string {
  if (!password) throw new Error('Choose a password first.');
  const decoded = nip19.decode(nsec.trim());
  if (decoded.type !== 'nsec') throw new Error('That is not a valid nsec.');
  return nip49.encrypt(decoded.data, password, LOG_N);
}

/** Decrypt a `ncryptsec` back to a bech32 `nsec`. Throws on a wrong password. */
export function decryptNcryptsec(ncryptsec: string, password: string): string {
  const value = ncryptsec.trim();
  if (!value.startsWith(NCRYPTSEC_PREFIX)) {
    throw new Error('That doesn’t look like an encrypted key (it should start with ncryptsec1).');
  }
  try {
    const secret = nip49.decrypt(value, password);
    return nip19.nsecEncode(secret);
  } catch {
    // The AEAD fails on a wrong password or a damaged blob; we can't tell which.
    throw new Error('Wrong password — or the encrypted key is damaged.');
  }
}

/** Cheap shape check so the UI can switch mode without a decode attempt. */
export function isNcryptsec(value: string): boolean {
  return value.trim().startsWith(NCRYPTSEC_PREFIX);
}