小程序怎么实现微信支付

/**
 * 预支付请求接口(POST)
 * @param string $openid 	openid
 * @param string $body 		商品简单描述
 * @param string $order_sn  订单编号
 * @param string $total_fee 金额
 * @return  json的数据
 */
public function prepay(){
	$config = $this->config;
	
	$openid = I('post.openid');
	$body = I('post.body');
	$order_sn = I('post.order_sn');
	$total_fee = I('post.total_fee');
	
	//统一下单参数构造
	$unifiedorder = array(
		'appid'			=> $config['appid'],
		'mch_id'		=> $config['pay_mchid'],
		'nonce_str'		=> self::getNonceStr(),
		'body'			=> $body,
		'out_trade_no'	=> $order_sn,
		'total_fee'		=> $total_fee * 100,
		'spbill_create_ip'	=> get_client_ip(),
		'notify_url'	=> 'https://'.$_SERVER['HTTP_HOST'].'/Api/Wxpay/notify',
		'trade_type'	=> 'JSAPI',
		'openid'		=> $openid
	);
	$unifiedorder['sign'] = self::makeSign($unifiedorder);
	//请求数据
	$xmldata = self::array2xml($unifiedorder);
	$url = 'https://api.mch.weixin.qq.com/pay/unifiedorder';
	$res = self::curl_post_ssl($url, $xmldata);
	if(!$res){
		self::return_err("Can't connect the server");
	}
	// 这句file_put_contents是用来查看服务器返回的结果 测试完可以删除了
	//file_put_contents(APP_ROOT.'/Statics/log1.txt',$res,FILE_APPEND);
	
	$content = self::xml2array($res);
	if(strval($content['result_code']) == 'FAIL'){
		self::return_err(strval($content['err_code_des']));
	}
	if(strval($content['return_code']) == 'FAIL'){
		self::return_err(strval($content['return_msg']));
	}
	self::return_data(array('data'=>$content));
	//$this->ajaxReturn($content);
}

/**
 * 进行支付接口(POST)
 * @param string $prepay_id 预支付ID(调用prepay()方法之后的返回数据中获取)
 * @return  json的数据
 */
public function pay(){
	$config = $this->config;
	$prepay_id = I('post.prepay_id');
	
	$data = array(
		'appId'		=> $config['appid'],
		'timeStamp'	=> time(),
		'nonceStr'	=> self::getNonceStr(),
		'package'	=> 'prepay_id='.$prepay_id,
		'signType'	=> 'MD5'
	);
	
	$data['paySign'] = self::makeSign($data);
	
	$this->ajaxReturn($data);
}

wx.requestPayment({
   'timeStamp': '',
   'nonceStr': '',
   'package': '',
   'signType': 'MD5',
   'paySign': '',
   'success':function(res){
   },
   'fail':function(res){
   }
})

//微信支付回调验证
public function notify(){
	$xml = $GLOBALS['HTTP_RAW_POST_DATA'];
	
	// 这句file_put_contents是用来查看服务器返回的XML数据 测试完可以删除了
	//file_put_contents(APP_ROOT.'/Statics/log2.txt',$res,FILE_APPEND);
	
	//将服务器返回的XML数据转化为数组
	$data = self::xml2array($xml);
	// 保存微信服务器返回的签名sign
	$data_sign = $data['sign'];
	// sign不参与签名算法
	unset($data['sign']);
	$sign = self::makeSign($data);
	
	// 判断签名是否正确  判断支付状态
	if ( ($sign===$data_sign) && ($data['return_code']=='SUCCESS') && ($data['result_code']=='SUCCESS') ) {
		$result = $data;
		//获取服务器返回的数据
		$order_sn = $data['out_trade_no'];			//订单单号
		$openid = $data['openid'];					//付款人openID
		$total_fee = $data['total_fee'];			//付款金额
		$transaction_id = $data['transaction_id']; 	//微信支付流水号
		
		//更新数据库
		$this->updateDB($order_sn,$openid,$total_fee,$transaction_id);
		
	}else{
		$result = false;
	}
	// 返回状态给微信服务器
	if ($result) {
		$str='<xml><return_code><![CDATA[SUCCESS]]></return_code><return_msg><![CDATA[OK]]></return_msg></xml>';
	}else{
		$str='<xml><return_code><![CDATA[FAIL]]></return_code><return_msg><![CDATA[签名失败]]></return_msg></xml>';
	}
	echo $str;
	return $result;
}

/**
 * 支付函数
 * @param  {[type]} _payInfo [description]
 * @return {[type]}          [description]
 */
pay:function(_payInfo,success,fail){
	var payInfo = {
		body:'',
		total_fee:0,
		order_sn:''
	}
	Object.assign(payInfo, _payInfo);
	if(payInfo.body.length==0){
		wx.showToast({
			title:'支付信息描述错误'
		})
		return false;
	}
	if(payInfo.total_fee==0){
		wx.showToast({
			title:'支付金额不能0'
		})
		return false; 
	}
	if(payInfo.order_sn.length==0){
		wx.showToast({
			title:'订单号不能为空'
		})
		return false; 
	}
	var This = this;
	This.getOpenid(function(openid){
		payInfo.openid=openid;
		This.request({
			url:'api/pay/prepay',
			data:payInfo,
			success:function(res){
				var data = res.data;
				console.log(data);
				if(!data.status){
					wx.showToast({
						title:data['errmsg']
					})
					return false;
				}
				This.request({
					url:'api/pay/pay',
					data:{prepay_id:data.data.data.prepay_id},
					success:function(_payResult){
						var payResult = _payResult.data;
						console.log(payResult);
						wx.requestPayment({
							'timeStamp': payResult.timeStamp.toString(),
							'nonceStr': payResult.nonceStr,
							'package': payResult.package,
							'signType': payResult.signType,
							'paySign': payResult.paySign,
							'success': function (succ) {
								success&&success(succ);
							},
							'fail': function (err) {
								fail&&fail(err);
							},
							'complete': function (comp) { 
 
							}
						}) 
					}
				})
			}
		})
	})
}