import {
  createDecipheriv,
  createSign,
  createVerify,
  randomBytes,
} from "node:crypto";

const WECHAT_PAY_API_BASE = "https://api.mch.weixin.qq.com";

type WechatNativeOrderParams = {
  appId: string;
  mchId: string;
  privateKey: string;
  serialNo: string;
  description: string;
  outTradeNo: string;
  notifyUrl: string;
  amountFen: number;
  attach?: string;
};

type WechatNativeOrderResponse = {
  code_url: string;
};

type WechatPayNotifyEnvelope = {
  id: string;
  create_time: string;
  event_type: string;
  resource_type: string;
  summary: string;
  resource: {
    algorithm: string;
    ciphertext: string;
    associated_data?: string;
    nonce: string;
  };
};

export class WechatPayError extends Error {
  status: number;

  constructor(message: string, status = 500) {
    super(message);
    this.status = status;
  }
}

function normalizePem(pem: string) {
  return pem.replace(/\\n/g, "\n").trim();
}

function buildWechatPaySignature({
  method,
  path,
  timestamp,
  nonce,
  body,
  privateKey,
}: {
  method: string;
  path: string;
  timestamp: string;
  nonce: string;
  body: string;
  privateKey: string;
}) {
  const message = `${method}\n${path}\n${timestamp}\n${nonce}\n${body}\n`;
  const signer = createSign("RSA-SHA256");
  signer.update(message);
  signer.end();
  return signer.sign(normalizePem(privateKey), "base64");
}

function buildWechatAuthorization({
  mchId,
  serialNo,
  timestamp,
  nonce,
  signature,
}: {
  mchId: string;
  serialNo: string;
  timestamp: string;
  nonce: string;
  signature: string;
}) {
  return `WECHATPAY2-SHA256-RSA2048 mchid=\"${mchId}\",nonce_str=\"${nonce}\",timestamp=\"${timestamp}\",serial_no=\"${serialNo}\",signature=\"${signature}\"`;
}

export function generateWechatOutTradeNo() {
  const suffix = randomBytes(4).toString("hex");
  return `LVT${Date.now()}${suffix}`.slice(0, 32);
}

export async function createWechatNativeOrder(params: WechatNativeOrderParams) {
  const path = "/v3/pay/transactions/native";
  const timestamp = `${Math.floor(Date.now() / 1000)}`;
  const nonce = randomBytes(16).toString("hex");
  const body = JSON.stringify({
    appid: params.appId,
    mchid: params.mchId,
    description: params.description,
    out_trade_no: params.outTradeNo,
    notify_url: params.notifyUrl,
    amount: {
      total: params.amountFen,
      currency: "CNY",
    },
    attach: params.attach,
  });

  const signature = buildWechatPaySignature({
    method: "POST",
    path,
    timestamp,
    nonce,
    body,
    privateKey: params.privateKey,
  });

  const authorization = buildWechatAuthorization({
    mchId: params.mchId,
    serialNo: params.serialNo,
    timestamp,
    nonce,
    signature,
  });

  const response = await fetch(`${WECHAT_PAY_API_BASE}${path}`, {
    method: "POST",
    headers: {
      Authorization: authorization,
      Accept: "application/json",
      "Content-Type": "application/json",
    },
    body,
  });

  const data = await response.json();

  if (!response.ok) {
    throw new WechatPayError(
      typeof data?.message === "string" ? data.message : "Failed to create WeChat native order",
      response.status
    );
  }

  if (!data?.code_url) {
    throw new WechatPayError("WeChat order response missing code_url", 502);
  }

  return data as WechatNativeOrderResponse;
}

export function verifyWechatPaySignature({
  body,
  timestamp,
  nonce,
  signature,
  platformPublicKey,
}: {
  body: string;
  timestamp: string;
  nonce: string;
  signature: string;
  platformPublicKey: string;
}) {
  const message = `${timestamp}\n${nonce}\n${body}\n`;
  const verifier = createVerify("RSA-SHA256");
  verifier.update(message);
  verifier.end();
  return verifier.verify(normalizePem(platformPublicKey), signature, "base64");
}

export function decryptWechatPayResource({
  ciphertext,
  nonce,
  associatedData,
  apiV3Key,
}: {
  ciphertext: string;
  nonce: string;
  associatedData?: string;
  apiV3Key: string;
}) {
  const key = Buffer.from(apiV3Key, "utf8");

  if (key.length !== 32) {
    throw new WechatPayError("WECHAT_PAY_API_V3_KEY must be 32 bytes", 500);
  }

  const data = Buffer.from(ciphertext, "base64");
  const authTag = data.subarray(data.length - 16);
  const encryptedData = data.subarray(0, data.length - 16);

  const decipher = createDecipheriv("aes-256-gcm", key, Buffer.from(nonce, "utf8"));
  if (associatedData) {
    decipher.setAAD(Buffer.from(associatedData, "utf8"));
  }
  decipher.setAuthTag(authTag);

  const plaintext = Buffer.concat([decipher.update(encryptedData), decipher.final()]).toString("utf8");

  return plaintext;
}

export function parseWechatNotifyPayload({
  body,
  apiV3Key,
}: {
  body: string;
  apiV3Key: string;
}) {
  const envelope = JSON.parse(body) as WechatPayNotifyEnvelope;
  const resource = envelope.resource;

  const plaintext = decryptWechatPayResource({
    ciphertext: resource.ciphertext,
    nonce: resource.nonce,
    associatedData: resource.associated_data,
    apiV3Key,
  });

  return {
    envelope,
    transaction: JSON.parse(plaintext) as Record<string, unknown>,
  };
}