import {
  createCipheriv,
  createDecipheriv,
  createHash,
  randomBytes,
  timingSafeEqual,
} from "node:crypto";

export class WecomCallbackCryptoError extends Error {
  status: number;

  constructor(message: string, status = 400) {
    super(message);
    this.name = "WecomCallbackCryptoError";
    this.status = status;
  }
}

export function resolveWecomCallbackAesKey(encodingAesKey: string): Buffer {
  const key = String(encodingAesKey ?? "").trim();
  if (!/^[A-Za-z0-9]{43}$/.test(key)) {
    throw new WecomCallbackCryptoError(
      "企业微信回调 EncodingAESKey 非法（需 43 位字母数字）",
      500,
    );
  }
  return Buffer.from(`${key}=`, "base64");
}

export function verifyWecomCallbackSignature(
  token: string,
  timestamp: string,
  nonce: string,
  encrypt: string,
): string {
  return createHash("sha1")
    .update([token, timestamp, nonce, encrypt].sort().join(""))
    .digest("hex");
}

export function wecomSignaturesMatch(
  expected: string,
  received: string,
): boolean {
  const a = Buffer.from(String(expected ?? ""));
  const b = Buffer.from(String(received ?? ""));
  if (a.length !== b.length || a.length === 0) return false;
  return timingSafeEqual(a, b);
}

export function encryptWecomCallback(
  plainMessage: string,
  receiveId: string,
  encodingAesKey: string,
): string {
  const key = resolveWecomCallbackAesKey(encodingAesKey);
  const random = randomBytes(16);
  const message = Buffer.from(String(plainMessage ?? ""), "utf8");
  const receive = Buffer.from(String(receiveId ?? ""), "utf8");
  const length = Buffer.alloc(4);
  length.writeUInt32BE(message.length, 0);
  const cipher = createCipheriv("aes-256-cbc", key, key.subarray(0, 16));
  const encrypted = Buffer.concat([
    cipher.update(Buffer.concat([random, length, message, receive])),
    cipher.final(),
  ]);
  return encrypted.toString("base64");
}

export function decryptWecomCallback(
  encrypted: string,
  encodingAesKey: string,
): { message: string; receiveId: string } {
  const key = resolveWecomCallbackAesKey(encodingAesKey);
  const data = Buffer.from(String(encrypted ?? "").trim(), "base64");
  if (data.length === 0 || data.length % 16 !== 0) {
    throw new WecomCallbackCryptoError("企业微信回调密文长度非法");
  }
  let raw: Buffer;
  try {
    const decipher = createDecipheriv("aes-256-cbc", key, key.subarray(0, 16));
    raw = Buffer.concat([decipher.update(data), decipher.final()]);
  } catch {
    throw new WecomCallbackCryptoError("企业微信回调密文解密失败");
  }
  if (raw.length < 20) {
    throw new WecomCallbackCryptoError("企业微信回调明文长度非法");
  }
  const messageLength = raw.readUInt32BE(16);
  if (messageLength <= 0 || 20 + messageLength > raw.length) {
    throw new WecomCallbackCryptoError("企业微信回调消息长度字段非法");
  }
  return {
    message: raw.subarray(20, 20 + messageLength).toString("utf8"),
    receiveId: raw.subarray(20 + messageLength).toString("utf8"),
  };
}