import { createCipheriv, createDecipheriv, createHash, randomBytes } from 'crypto';
import { envOrNull } from '../../common/env';

/**
 * Encrypts the accounting-software token at rest (D27).
 *
 * The token sits in the Setting table, so a database dump or a backup would
 * otherwise hand out a live credential to the shop's books. AES-256-GCM with a
 * key derived from `ACCOUNTING_SECRET_KEY`.
 *
 * When that variable is unset the key falls back to one derived from
 * `JWT_SECRET`, with a loud warning at boot — the same "warn, don't refuse"
 * trade-off D23 made — so an admin can configure the integration before ops
 * add the variable. The cost: rotating JWT_SECRET then makes the stored token
 * unreadable and the admin has to enter it again (the screen says so).
 */

const PREFIX = 'enc:v1:';

export function secretKeySource(): 'ACCOUNTING_SECRET_KEY' | 'JWT_SECRET' | null {
  if (envOrNull('ACCOUNTING_SECRET_KEY')) return 'ACCOUNTING_SECRET_KEY';
  if (envOrNull('JWT_SECRET')) return 'JWT_SECRET';
  return null;
}

function key(): Buffer {
  const material = envOrNull('ACCOUNTING_SECRET_KEY') ?? envOrNull('JWT_SECRET');
  if (!material) {
    throw new Error('ACCOUNTING_SECRET_KEY تنظیم نشده است؛ ذخیره‌ی توکن حسابداری ممکن نیست.');
  }
  return createHash('sha256').update(`goldbank-accounting:${material}`).digest();
}

export function sealSecret(plain: string): string {
  const iv = randomBytes(12);
  const cipher = createCipheriv('aes-256-gcm', key(), iv);
  const body = Buffer.concat([cipher.update(plain, 'utf8'), cipher.final()]);
  const tag = cipher.getAuthTag();
  return PREFIX + Buffer.concat([iv, tag, body]).toString('base64');
}

/** Null when the value cannot be decrypted (wrong key, tampered, malformed). */
export function openSecret(sealed: string | null | undefined): string | null {
  if (!sealed || !sealed.startsWith(PREFIX)) return null;
  try {
    const raw = Buffer.from(sealed.slice(PREFIX.length), 'base64');
    const iv = raw.subarray(0, 12);
    const tag = raw.subarray(12, 28);
    const body = raw.subarray(28);
    const decipher = createDecipheriv('aes-256-gcm', key(), iv);
    decipher.setAuthTag(tag);
    return Buffer.concat([decipher.update(body), decipher.final()]).toString('utf8');
  } catch {
    return null;
  }
}