//index.js
const express = require('express');
const url = require('url');
const wechatqr = require('./wechatqr');

const app = express();

app.get('接口地址', function(req, res) {
//接收参数，自行换成你的
//接口效果如https://baidu.com/接口地址?objectId=123;
	let objectId = url.parse(req.url, true).query.objectId;
	if (typeof objectId !== 'string' || objectId.length == 0) {
		res.json({
			code: 0
		})
	} else {
		wechatqr.getQR(objectId, '扫码后打开的小程序页面路径').then((data) => {
			res.json({
				qrimg: data,
				code: 1
			})
		}).catch((err) => {
			console.log(err)
			res.json({
				code: 0
			})
		});
	}
});

var server = app.listen(3000, function() {

});

//wechatqr.js
const request = require("request");
const rp = require("request-promise-native");
const fs = require("fs");
const crypto = require('crypto');
const token = require('./wechattoken');

function sha1(message) {
	return crypto.createHash('sha1').update(message, 'utf8').digest('hex');
}

function checkFile(filePath) {
	return new Promise(function(resolve, reject) {
		fs.access(filePath, fs.constants.R_OK, (err) => {
			if (err)
				reject()
			else
				resolve()
		});
	})
}

function getQR(scene, path) {
	let fileName = sha1(scene),
		filePath = `../webpage/postcard/static/qrimg/${fileName}.png`,
		imgPath = `https://static.postcard.daibor.cn/qrimg/${fileName}.png`,
		readable;

	return new Promise(function(resolve, reject) {
		//检查文件是否存在
		checkFile(filePath).then((res) => {
			//无错误，有文件
			console.log('existed');
			resolve(imgPath);
		}).catch((err) => {
			//有错误，无文件
			console.log('new user');
			var saveQR = request({
				url: 'https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=' + token.getToken(),
				method: 'POST',
				headers: {
					'content-type': 'application/json'
				},
				body: JSON.stringify({
					scene: scene,
					page: path,
					is_hyaline: true
				})
			}).pipe(fs.createWriteStream(filePath));
			saveQR.on('finish', function() {
				resolve(imgPath);
			})
		})
	})
}

module.exports = {
	getQR
}

//wechattoken.js
const cf = require('./conf');
const rp = require("request-promise-native");

var _TOKEN = '';
//请求access_token
function getAccessToken() {
	rp('https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=' + cf.appid + '&secret=' + cf.secret).then((res) => {
		console.log(res);
		_TOKEN = JSON.parse(res).access_token;
	})
}

function getToken() {
	return _TOKEN;
}

getAccessToken();

//微信规定超时时间7200秒，不能频繁请求，因此设置每7000秒重新请求一次。
const _timer = setInterval(getAccessToken, 7000000);

module.exports = {
	getToken
}

//conf.js
module.exports = {
	appid: 你的小程序id,
	secret: 你的小程序secret
}