/**
 * 前后端通信 AES-256-GCM 加解密工具（前端浏览器环境）
 *
 * 使用 PBKDF2-HMAC-SHA256 从 NEXT_PUBLIC_ENCRYPTION_SECRET 派生密钥，
 * 与 crypto-server.ts 共享相同的算法和参数，实现前后端加解密互通。
 *
 * 参考同级项目 novavis-authority 的加解密方案。
 *
 * 输出格式: Base64(12-byte-IV || AES-GCM-ciphertext)
 */

const IV_LENGTH = 12;
const ALGORITHM = 'AES-GCM';
const PBKDF2_ITERATIONS = 100_000;
const PBKDF2_SALT = new TextEncoder().encode('novalon-website-crypto-salt-v1');

async function deriveKey(passphrase: string): Promise<CryptoKey> {
  const encoder = new TextEncoder();
  const keyMaterial = await crypto.subtle.importKey(
    'raw',
    encoder.encode(passphrase),
    'PBKDF2',
    false,
    ['deriveBits', 'deriveKey'],
  );
  return crypto.subtle.deriveKey(
    { name: 'PBKDF2', salt: PBKDF2_SALT, iterations: PBKDF2_ITERATIONS, hash: 'SHA-256' },
    keyMaterial,
    { name: ALGORITHM, length: 256 },
    false,
    ['encrypt', 'decrypt'],
  );
}

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

let cachedKey: Promise<CryptoKey> | null = null;

function getKey(): Promise<CryptoKey> {
  if (!cachedKey) {
    cachedKey = deriveKey(getSecret());
  }
  return cachedKey;
}

/**
 * 加密明文，返回 Base64 编码的密文（IV 前置）
 */
export async function encrypt(plaintext: string): Promise<string> {
  const key = await getKey();
  const iv = crypto.getRandomValues(new Uint8Array(IV_LENGTH));
  const encoder = new TextEncoder();
  const ciphertext = await crypto.subtle.encrypt(
    { name: ALGORITHM, iv, tagLength: 128 },
    key,
    encoder.encode(plaintext),
  );

  const combined = new Uint8Array(IV_LENGTH + ciphertext.byteLength);
  combined.set(iv, 0);
  combined.set(new Uint8Array(ciphertext), IV_LENGTH);

  return btoa(Array.from(combined, (b) => String.fromCodePoint(b)).join(''));
}

/**
 * 解密 Base64 编码的密文（IV 前置），返回明文字符串
 */
export async function decrypt(encryptedBase64: string): Promise<string> {
  const key = await getKey();
  const binaryStr = atob(encryptedBase64);
  const combined = new Uint8Array(binaryStr.length);
  for (let i = 0; i < binaryStr.length; i++) {
    combined[i] = binaryStr.codePointAt(i)!;
  }

  const iv = combined.slice(0, IV_LENGTH);
  const ciphertext = combined.slice(IV_LENGTH);

  const decrypted = await crypto.subtle.decrypt(
    { name: ALGORITHM, iv, tagLength: 128 },
    key,
    ciphertext,
  );

  return new TextDecoder().decode(decrypted);
}