利用thinkPHP怎么实现一个微信支付功能

 //实现的Wxpay钩子方法
    public function Wxpay($param){
      require './Addons/Wxpay/WxPayPubHelper/WxPayPubHelper.php';
      $jsApi = new \JsApi_pub(); 
      
      //=========步骤1：网页授权获取用户openid============
      if (!isset($_GET['code']))
      {
        //触发微信返回code码
        $url = $jsApi->createOauthUrlForCode(\WxPayConf_pub::JS_API_CALL_URL.'/order_id/'.$param['order_id']);
        Header("Location: $url");
      }else
      {
        $order_id = $param['order_id'];
        $info = M('Order')->where('id='.$order_id)->find();
        if(empty($info) || $info['is_pay'] == 1){
          dump('该订单不存在或已支付'.$order_id);
          exit();
        }
        $this->assign('info',$info);
        $a = $info['money'];
        $b = 100;
        $c = $a * $b;
        
        //获取code码，以获取openid
        $code = $_GET['code'];
        $jsApi->setCode($code);
        $openid = $jsApi->getOpenId();
      }
       
      //=========步骤2：使用统一支付接口，获取prepay_id============
      //使用统一支付接口
      $unifiedOrder = new \UnifiedOrder_pub();
       
      $unifiedOrder->setParameter("openid","$openid");//商品描述
      $unifiedOrder->setParameter("body","在线预订");//商品描述
      //自定义订单号，此处仅作举例
      $timeStamp = time();
//       $out_trade_no = \WxPayConf_pub::APPID."$timeStamp";
      $out_trade_no = $info['ordersn'];
      $unifiedOrder->setParameter("out_trade_no","$out_trade_no");//商户订单号
      $unifiedOrder->setParameter("total_fee","$c");//总金额
      $unifiedOrder->setParameter("notify_url",\WxPayConf_pub::NOTIFY_URL.'/order_id/'.$param['order_id']);//通知地址
      $unifiedOrder->setParameter("trade_type","JSAPI");//交易类型
       
      $prepay_id = $unifiedOrder->getPrepayId();
      //=========步骤3：使用jsapi调起支付============
      $jsApi->setPrepayId($prepay_id);
      $jsApiParameters = $jsApi->getParameters();
      $this->assign('jsApiParameters',$jsApiParameters);
 
      $this->display('pay');
    }