const axios = require('axios')
const crypto = require('crypto')
const fs = require('fs')
const path = require('path')

/**
 * 微信小程序 API 工具类
 */
class WeChatService {
  constructor() {
    this.appId = process.env.WX_APPID
    this.secret = process.env.WX_SECRET
    this.mchId = process.env.WX_PAY_MCH_ID
    this.apiKey = process.env.WX_PAY_API_KEY // APIv3 Key
    this.serialNo = process.env.WX_PAY_SERIAL_NO
    this.notifyUrl = process.env.WX_PAY_NOTIFY_URL
    
    // 加载证书
    try {
      const certPath = path.join(__dirname, '../../certs/apiclient_cert.pem')
      const keyPath = path.join(__dirname, '../../certs/apiclient_key.pem')
      this.privateKey = fs.readFileSync(keyPath)
      this.certificate = fs.readFileSync(certPath)
    } catch (error) {
      console.error('微信支付证书加载失败，请检查 certs 目录:', error.message)
    }
    
    // 缓存 access_token
    this.accessToken = null
    this.tokenExpireTime = 0
  }

  /**
   * 微信支付 v3 是否配置完整（商户号+序列号+商户私钥）
   */
  isPayConfigured() {
    return !!(this.mchId && this.serialNo && this.privateKey)
  }

  /**
   * 生成微信支付 v3 请求头 Authorization（商户私钥签名）
   */
  buildV3Auth(method, urlPath, timestamp, nonce, bodyStr) {
    const message = `${method}\n${urlPath}\n${timestamp}\n${nonce}\n${bodyStr}\n`
    const signer = crypto.createSign('RSA-SHA256')
    signer.update(message)
    signer.end()
    const signature = signer.sign(this.privateKey, 'base64')
    return `WECHATPAY2-SHA256-RFC4648 mchid="${this.mchId}",nonce_str="${nonce}",signature="${signature}",timestamp="${timestamp}",serial_no="${this.serialNo}"`
  }
  
  /**
   * 获取 Access Token
   */
  async getAccessToken() {
    // 检查缓存
    if (this.accessToken && Date.now() < this.tokenExpireTime) {
      return this.accessToken
    }
    
    try {
      const response = await axios.get('https://api.weixin.qq.com/cgi-bin/token', {
        params: {
          grant_type: 'client_credential',
          appid: this.appId,
          secret: this.secret
        }
      })
      
      if (response.data.errcode) {
        throw new Error(response.data.errmsg)
      }
      
      this.accessToken = response.data.access_token
      this.tokenExpireTime = Date.now() + (response.data.expires_in - 300) * 1000 // 提前5分钟过期
      
      return this.accessToken
    } catch (error) {
      console.error('获取 Access Token 失败:', error)
      throw error
    }
  }
  
  /**
   * 通过 code 换取 openid 和 session_key
   */
  async code2Session(code) {
    try {
      const response = await axios.get('https://api.weixin.qq.com/sns/jscode2session', {
        params: {
          appid: this.appId,
          secret: this.secret,
          js_code: code,
          grant_type: 'authorization_code'
        }
      })
      
      if (response.data.errcode && response.data.errcode !== 0) {
        throw new Error(response.data.errmsg)
      }
      
      return {
        openid: response.data.openid,
        sessionKey: response.data.session_key,
        unionid: response.data.unionid
      }
    } catch (error) {
      console.error('code2Session 失败:', error)
      throw error
    }
  }
  
  /**
   * 生成随机字符串
   */
  generateNonceStr(length = 32) {
    const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'
    let result = ''
    for (let i = 0; i < length; i++) {
      result += chars.charAt(Math.floor(Math.random() * chars.length))
    }
    return result
  }
  
  /**
   * 生成订单号
   */
  generateOrderNo(prefix = 'WD') {
    const date = new Date()
    const dateStr = date.getFullYear().toString() +
      String(date.getMonth() + 1).padStart(2, '0') +
      String(date.getDate()).padStart(2, '0')
    const randomStr = Math.random().toString(36).substr(2, 6).toUpperCase()
    return `${prefix}${dateStr}${randomStr}`
  }
  
  /**
   * 生成签名
   */
  generateSign(method, url, timestamp, nonceStr, body = '') {
    const signStr = `${method}\n${url}\n${timestamp}\n${nonceStr}\n${body}\n`
    const sign = crypto.createSign('RSA-SHA256')
    sign.update(signStr)
    sign.end()
    return sign.sign(this.privateKey, 'base64')
  }

  /**
   * 创建支付订单（小程序支付 - 真实流程）
   */
  async createPaymentOrder(orderData) {
    const { openid, orderNo, body, amount } = orderData
    
    const nonceStr = this.generateNonceStr()
    const timestamp = Math.floor(Date.now() / 1000).toString()
    
    // 1. 统一下单 (JSAPI)
    const url = '/v3/pay/transactions/jsapi'
    const fullUrl = `https://api.mch.weixin.qq.com${url}`
    
    const orderParams = {
      appid: this.appId,
      mchid: this.mchId,
      description: body,
      out_trade_no: orderNo,
      notify_url: this.notifyUrl,
      amount: {
        total: Math.round(amount), // 金额单位已为分
        currency: 'CNY'
      },
      payer: {
        openid: openid
      }
    }

    if (!this.isPayConfigured()) {
      const err = new Error('支付功能暂未开通：缺少商户证书配置，请联系管理员在服务器放置 apiclient_key.pem 后重启服务')
      err.code = 'PAY_NOT_CONFIGURED'
      throw err
    }

    try {
      // 1. 统一下单（真·微信支付 v3 JSAPI）
      const bodyStr = JSON.stringify(orderParams)
      const auth = this.buildV3Auth('POST', url, timestamp, nonceStr, bodyStr)
      const controller = new AbortController()
      const timer = setTimeout(() => controller.abort(), 15000)
      let response
      try {
        response = await axios.post(fullUrl, bodyStr, {
          headers: {
            'Content-Type': 'application/json',
            Accept: 'application/json',
            Authorization: auth,
            'User-Agent': 'yuzhiran-ai-dimension/1.2'
          },
          timeout: 15000,
          signal: controller.signal
        })
      } finally {
        clearTimeout(timer)
      }

      const prepayId = response.data && response.data.prepay_id
      if (!prepayId) {
        throw new Error('微信支付下单未返回 prepay_id')
      }

      // 2. 生成前端调起支付的签名（appId/timeStamp/nonceStr/package 四行拼接）
      const paySignStr = `${this.appId}\n${timestamp}\n${nonceStr}\nprepay_id=${prepayId}\n`
      const paySign = crypto.createSign('RSA-SHA256')
      paySign.update(paySignStr)
      paySign.end()
      const signature = paySign.sign(this.privateKey, 'base64')

      return {
        appId: this.appId,
        timeStamp: timestamp,
        nonceStr,
        package: `prepay_id=${prepayId}`,
        signType: 'RSA',
        paySign: signature,
        orderNo
      }
    } catch (error) {
      console.error('微信支付下单失败:', error.response ? error.response.data : error.message)
      if (error.code === 'PAY_NOT_CONFIGURED') throw error
      const wxMsg = error.response && error.response.data && error.response.data.message
      throw new Error(wxMsg ? `微信支付下单失败：${wxMsg}` : '微信支付下单失败，请稍后再试')
    }
  }
  
  /**
   * 创建H5支付订单（微信H5支付/MWEB）
   * @param {Object} orderData - { orderNo, body, amount, clientIp, appId }
   */
  async createH5PaymentOrder(orderData) {
    const { orderNo, body, amount, clientIp, appId } = orderData
    
    const nonceStr = this.generateNonceStr()
    const timestamp = Math.floor(Date.now() / 1000).toString()
    
    // 1. 统一下单 (H5 / MWEB)
    const url = '/v3/pay/transactions/h5'
    const fullUrl = `https://api.mch.weixin.qq.com${url}`
    
    const orderParams = {
      appid: appId || this.appId,
      mchid: this.mchId,
      description: body,
      out_trade_no: orderNo,
      notify_url: this.notifyUrl,
      amount: {
        total: Math.round(amount), // 金额单位已为分
        currency: 'CNY'
      },
      scene_info: {
        h5_info: {
          type: 'Wap',
          client_ip: clientIp
        }
      }
    }
    
    // 模拟返回 h5_url (生产环境需调用真实微信支付接口)
    // 实际生产调用示例:
    // const sign = this.generateSign('POST', url, timestamp, nonceStr, JSON.stringify(orderParams))
    // const response = await axios.post(fullUrl, orderParams, {
    //   headers: { 'Authorization': `WECHATPAY2-SHA256-RSA2048 ${sign}` }
    // })
    // const h5Url = response.data.h5_url
    
    // 模拟 H5 支付链接（生产环境由微信返回真实 MWEB_URL）
    const mockH5Url = `https://wx.tenpay.com/cgi-bin/mmpayweb-bin/checkmweb?prepay_id=wx_mock_${Date.now()}&package=mock_${Date.now()}`
    
    return {
      h5Url: mockH5Url,
      orderNo,
      amount: Math.round(amount)
    }
  }
  
  /**
   * 申请退款
   */
  async refundOrder(transactionId, outRefundNo, totalAmount, refundAmount, reason = '用户申请退款') {
    const url = '/v3/refund/domestic/refunds'
    const fullUrl = `https://api.mch.weixin.qq.com${url}`
    
    const nonceStr = this.generateNonceStr()
    const timestamp = Math.floor(Date.now() / 1000).toString()
    
    const refundParams = {
      transaction_id: transactionId,
      out_refund_no: outRefundNo,
      reason: reason,
      notify_url: this.notifyUrl.replace('/callback', '/refund-callback'), // 假设退款回调地址
      amount: {
        refund: Math.round(refundAmount * 100),
        total: Math.round(totalAmount * 100),
        currency: 'CNY'
      }
    }

    try {
      // 注意：实际生产环境需要处理网络请求和签名
      // const sign = this.generateSign('POST', url, timestamp, nonceStr, JSON.stringify(refundParams))
      // const response = await axios.post(fullUrl, refundParams, { ... })
      
      console.log('[WeChat] 模拟退款请求:', refundParams)
      return { success: true, message: '退款申请已提交' }
    } catch (error) {
      console.error('微信支付退款失败:', error)
      throw error
    }
  }
  
  /**
   * 验证支付回调签名
   */
  verifyCallbackSignature(data, sign) {
    // 实际应使用微信支付 V3 的签名验证方法
    // 这里仅作示例
    return true
  }
}

// 导出单例
const weChatService = new WeChatService()

module.exports = weChatService