/**
 * 凭证密封 —— ADR-009。app 层持有主密钥,模块只见 `SecretBox` 端口。
 *
 * 密文格式:`v1.<iv>.<tag>.<cipher>`(均 base64url)。
 */
import { createCipheriv, createDecipheriv, createHash, randomBytes } from 'node:crypto';
import type { SecretBox } from '@modules/llm';

const DEV_SALT = 'jcai-dev-only-not-for-production';

export function loadSecretKey(env: NodeJS.ProcessEnv = process.env): Buffer {
  const raw = env['JCAI_SECRET_KEY'];
  if (raw !== undefined && raw !== '') {
    const key = Buffer.from(raw, 'base64');
    if (key.length !== 32) throw new Error('JCAI_SECRET_KEY 必须是 32 字节的 base64');
    return key;
  }
  if (env['NODE_ENV'] === 'production') {
    throw new Error('生产环境必须设置 JCAI_SECRET_KEY(ADR-009)');
  }
  process.stderr.write('⚠️  JCAI_SECRET_KEY 未设置,使用开发派生密钥 —— 切勿用于生产(ADR-009)\n');
  return createHash('sha256').update(DEV_SALT).digest();
}

export function createSecretBox(key: Buffer): SecretBox {
  return {
    seal(plaintext) {
      const iv = randomBytes(12);
      const cipher = createCipheriv('aes-256-gcm', key, iv);
      const enc = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()]);
      return ['v1', iv.toString('base64url'), cipher.getAuthTag().toString('base64url'), enc.toString('base64url')].join('.');
    },
    open(text) {
      const [version, ivRaw, tagRaw, cipherRaw] = text.split('.');
      if (version !== 'v1' || ivRaw === undefined || tagRaw === undefined || cipherRaw === undefined) {
        throw new Error('密文格式非法');
      }
      const decipher = createDecipheriv('aes-256-gcm', key, Buffer.from(ivRaw, 'base64url'));
      decipher.setAuthTag(Buffer.from(tagRaw, 'base64url'));
      return Buffer.concat([decipher.update(Buffer.from(cipherRaw, 'base64url')), decipher.final()]).toString('utf8');
    },
  };
}