const express = require('express');
const router = express.Router();
const crypto = require('crypto');
const axios = require('axios');
const xml2js = require('xml2js');
const { v4: uuidv4 } = require('uuid');
const QRCode = require('qrcode');
const config = require('../config');
const storage = require('../utils/storage');

function buildSign(params, key) {
  const str = Object.keys(params)
    .filter(k => params[k] !== '' && k !== 'sign')
    .sort()
    .map(k => `${k}=${params[k]}`)
    .join('&') + `&key=${key}`;
  return crypto.createHash('md5').update(str, 'utf-8').digest('hex').toUpperCase();
}

function buildXml(obj) {
  let xml = '<xml>';
  for (const [k, v] of Object.entries(obj)) {
    xml += `<${k}>${v}</${k}>`;
  }
  xml += '</xml>';
  return xml;
}

// Step 1: Create order page - show QR code
router.get('/create/:productId', async (req, res) => {
  const product = config.products.find(p => p.id === parseInt(req.params.productId));
  if (!product) return res.status(404).send('商品不存在');

  const orderId = uuidv4().replace(/-/g, '').substring(0, 28);
  const order = {
    orderId,
    productId: product.id,
    productName: product.name,
    totalFee: product.price,
    status: 'CREATING',
    createdAt: new Date().toISOString(),
    updatedAt: new Date().toISOString(),
  };
  storage.saveOrder(order);

  try {
    const nonceStr = uuidv4().replace(/-/g, '').substring(0, 16);
    const unifiedParams = {
      appid: config.wechat.appid,
      mch_id: config.wechat.mchid,
      nonce_str: nonceStr,
      body: product.name,
      out_trade_no: orderId,
      total_fee: product.price,
      spbill_create_ip: req.ip || '127.0.0.1',
      notify_url: config.wechat.notifyUrl,
      trade_type: 'NATIVE',
    };
    unifiedParams.sign = buildSign(unifiedParams, config.wechat.key);

    const xml = buildXml(unifiedParams);
    const resp = await axios.post(
      `${config.wechat.apiBase}/pay/unifiedorder`,
      xml,
      { headers: { 'Content-Type': 'text/xml' } }
    );

    const parsed = await xml2js.parseStringPromise(resp.data, { explicitArray: false });
    const result = parsed.xml;

    if (result.return_code !== 'SUCCESS' || result.result_code !== 'SUCCESS') {
      order.status = 'FAILED';
      storage.saveOrder(order);
      return res.render('pay', { error: `下单失败: ${result.err_code_des || result.return_msg}` });
    }

    order.codeUrl = result.code_url;
    order.status = 'PENDING';
    storage.saveOrder(order);

    const qrDataUrl = await QRCode.toDataURL(result.code_url, { width: 300, margin: 2 });
    res.render('pay', { order, qrDataUrl, error: null });
  } catch (err) {
    order.status = 'FAILED';
    storage.saveOrder(order);
    res.render('pay', { error: `系统错误: ${err.message}` });
  }
});

// Step 2: Poll payment status
router.get('/status/:orderId', (req, res) => {
  const order = storage.findOrder(req.params.orderId);
  if (!order) return res.json({ status: 'NOT_FOUND' });
  res.json({ status: order.status, orderId: order.orderId });
});

// Step 3: WeChat payment notification callback
router.post('/notify', async (req, res) => {
  if (!req.body) {
    return res.send(buildXml({ return_code: 'FAIL', return_msg: '空请求体' }));
  }

  try {
    const parsed = await xml2js.parseStringPromise(req.body, { explicitArray: false });
    const data = parsed.xml;

    const expectedSign = buildSign(data, config.wechat.key);
    if (data.sign !== expectedSign) {
      return res.send(buildXml({ return_code: 'FAIL', return_msg: '签名失败' }));
    }

    if (data.return_code === 'SUCCESS' && data.result_code === 'SUCCESS') {
      storage.updateOrderStatus(data.out_trade_no, 'SUCCESS', data.transaction_id);
      return res.send(buildXml({ return_code: 'SUCCESS', return_msg: 'OK' }));
    }

    res.send(buildXml({ return_code: 'FAIL', return_msg: data.err_code_des || '支付失败' }));
  } catch (err) {
    res.send(buildXml({ return_code: 'FAIL', return_msg: '解析失败' }));
  }
});

// Step 4: Order list
router.get('/orders', (req, res) => {
  const orders = storage.readOrders().sort((a, b) => new Date(b.createdAt) - new Date(a.createdAt));
  res.render('orders', { orders });
});

// Success page
router.get('/success/:orderId', (req, res) => {
  const order = storage.findOrder(req.params.orderId);
  if (!order) return res.status(404).send('订单不存在');
  res.render('success', { order });
});

module.exports = router;