/**
 * 服务端 AES-256-GCM 加解密工具（Node.js 环境）
 *
 * 使用 PBKDF2-HMAC-SHA256 从 ENCRYPTION_SECRET 派生密钥，
 * 与 crypto.ts 共享相同的算法和参数，实现前后端加解密互通。
 *
 * 供 Next.js API Route 在服务端解密请求体、加密响应体。
 */

import crypto from 'node:crypto';

const ALGORITHM = 'aes-256-gcm';
const IV_LENGTH = 12;
const AUTH_TAG_LENGTH = 16;
const PBKDF2_ITERATIONS = 100_000;
const PBKDF2_SALT = 'novalon-website-crypto-salt-v1';
const KEY_LENGTH = 32; // 256 bits

function getSecret(): string {
  const secret = process.env.ENCRYPTION_SECRET;
  if (!secret) {
    throw new Error('ENCRYPTION_SECRET 未配置，服务端加解密无法初始化');
  }
  return secret;
}

let cachedKey: Buffer | null = null;

function deriveKey(): Buffer {
  if (cachedKey) return cachedKey;
  const secret = getSecret();
  cachedKey = crypto.pbkdf2Sync(
    secret,
    PBKDF2_SALT,
    PBKDF2_ITERATIONS,
    KEY_LENGTH,
    'sha256',
  );
  return cachedKey;
}

/**
 * 加密明文，返回 Base64 编码的密文（12-byte-IV || AES-GCM-ciphertext）
 */
export function encrypt(plaintext: string): string {
  const key = deriveKey();
  const iv = crypto.randomBytes(IV_LENGTH);
  const cipher = crypto.createCipheriv(ALGORITHM, key, iv);

  const encrypted = Buffer.concat([
    cipher.update(plaintext, 'utf8'),
    cipher.final(),
  ]);
  const authTag = cipher.getAuthTag();

  // 格式: iv + authTag + encrypted
  const combined = Buffer.concat([iv, authTag, encrypted]);
  return combined.toString('base64');
}

/**
 * 解密 Base64 编码的密文，返回明文字符串
 */
export function decrypt(encryptedBase64: string): string {
  const key = deriveKey();
  const combined = Buffer.from(encryptedBase64, 'base64');

  const iv = combined.subarray(0, IV_LENGTH);
  const authTag = combined.subarray(IV_LENGTH, IV_LENGTH + AUTH_TAG_LENGTH);
  const encrypted = combined.subarray(IV_LENGTH + AUTH_TAG_LENGTH);

  const decipher = crypto.createDecipheriv(ALGORITHM, key, iv);
  decipher.setAuthTag(authTag);

  const decrypted = Buffer.concat([
    decipher.update(encrypted),
    decipher.final(),
  ]);

  return decrypted.toString('utf8');
}

/**
 * 验证加密配置是否可用
 */
export function isEncryptionAvailable(): boolean {
  return !!process.env.ENCRYPTION_SECRET;
}