// services/cryptoUtil.js
// Symmetric encryption for secrets we must be able to READ back (unlike
// portal passwords, which are one-way hashed) — specifically each user's SAP
// Service-Layer password, which has to be replayed to SAP at login time.
// AES-256-GCM with a key derived from JWT_SECRET. Output is a self-describing
// string "v1:<iv>:<tag>:<ciphertext>" (all base64), so decrypt needs no extra
// state. NOT for passwords you only ever compare — use hashing for those.
'use strict';
const crypto = require('crypto');

function key() {
  const secret = process.env.JWT_SECRET || 'sap-portal-secret';
  return crypto.createHash('sha256').update('sapcred:' + secret).digest(); // 32 bytes
}

function encrypt(plain) {
  if (plain == null || plain === '') return '';
  const iv = crypto.randomBytes(12);
  const cipher = crypto.createCipheriv('aes-256-gcm', key(), iv);
  const enc = Buffer.concat([cipher.update(String(plain), 'utf8'), cipher.final()]);
  const tag = cipher.getAuthTag();
  return `v1:${iv.toString('base64')}:${tag.toString('base64')}:${enc.toString('base64')}`;
}

function decrypt(blob) {
  if (!blob) return '';
  try {
    const parts = String(blob).split(':');
    if (parts.length !== 4 || parts[0] !== 'v1') return '';
    const iv = Buffer.from(parts[1], 'base64');
    const tag = Buffer.from(parts[2], 'base64');
    const data = Buffer.from(parts[3], 'base64');
    const decipher = crypto.createDecipheriv('aes-256-gcm', key(), iv);
    decipher.setAuthTag(tag);
    return Buffer.concat([decipher.update(data), decipher.final()]).toString('utf8');
  } catch { return ''; }
}

module.exports = { encrypt, decrypt };