text: const fs = require('fs')
  const path = require('path')
  const LRU = require('lru-cache')
  const express = require('express')
  const favicon = require('serve-favicon')
  const compression = require('compression')
  const resolve = file => path.resolve(__dirname, file)
  const { createBundleRenderer } = require('vue-server-renderer')
  const redirects = require('./src/router/301.json')
  
  const isProd = process.env.NODE_ENV === 'production'
  const useMicroCache = process.env.MICRO_CACHE !== 'false'
  const serverInfo =
    `express/${require('express/package.json').version} ` +
    `vue-server-renderer/${require('vue-server-renderer/package.json').version}`
  
  const app = express()
  
  const template = fs.readFileSync(resolve('./assets/index.template.html'), 'utf-8')
  
  function createRenderer (bundle, options) {
    // https://github.com/vuejs/vue/blob/dev/packages/vue-server-renderer/README.md#why-use-bundlerenderer
    return createBundleRenderer(bundle, Object.assign(options, {
      template,
      // for component caching
      cache: LRU({
        max: 1000,
        maxAge: 1000 * 60 * 15
      }),
      // this is only needed when vue-server-renderer is npm-linked
      basedir: resolve('./public'),
      // recommended for performance
      runInNewContext: false
    }))
  }
  
  let renderer
  let readyPromise
  if (isProd) {
    // In production: create server renderer using built server bundle.
    // The server bundle is generated by vue-ssr-webpack-plugin.
    const bundle = require('./public/vue-ssr-server-bundle.json')
    // The client manifests are optional, but it allows the renderer
    // to automatically infer preload/prefetch links and directly add <script>
    // tags for any async chunks used during render, avoiding waterfall requests.
    const clientManifest = require('./public/vue-ssr-client-manifest.json')
    renderer = createRenderer(bundle, {
      clientManifest
    })
  } else {
    // In development: setup the dev server with watch and hot-reload,
    // and create a new renderer on bundle / index template update.
    readyPromise = require('./build/setup-dev-server')(app, (bundle, options) => {
      renderer = createRenderer(bundle, options)
    })
  }
  
  const serve = (path, cache) => express.static(resolve(path), {
    maxAge: cache && isProd ? 60 * 60 * 24 * 30 : 0
  })
  
  app.use(compression({ threshold: 0 }))
  app.use(favicon('./static/favicon.ico'))
  app.use('/static', serve('./static', true))
  app.use('/public', serve('./public', true))
  app.use('/static/robots.txt', serve('./robots.txt'))
  
  app.get('/sitemap.xml', (req, res) => {
    res.setHeader("Content-Type", "text/xml")
    res.sendFile(resolve('./public/sitemap.xml'))
  })
  
  // 301 redirect for changed routes
  Object.keys(redirects).forEach(k => {
    app.get(k, (req, res) => res.redirect(301, redirects[k]))
  })
  
  // 1-second microcache.
  // https://www.nginx.com/blog/benefits-of-microcaching-nginx/
  const microCache = LRU({
    max: 100,
    maxAge: 1000
  })
  
  // since this app has no user-specific content, every page is micro-cacheable.
  // if your app involves user-specific content, you need to implement custom
  // logic to determine whether a request is cacheable based on its url and
  // headers.
  const isCacheable = req => useMicroCache
  
  function render (req, res) {
    const s = Date.now()
  
    res.setHeader("Content-Type", "text/html")
    res.setHeader("Server", serverInfo)
  
    const handleError = err => {
      if (err && err.code === 404) {
        res.status(404).end('404 | Page Not Found')
      } else {
        // Render Error Page or Redirect
        res.status(500).end('500 | Internal Server Error')
        console.error(`error during render : ${req.url}`)
        console.error(err.stack)
      }
    }
  
    const cacheable = isCacheable(req)
    if (cacheable) {
      const hit = microCache.get(req.url)
      if (hit) {
        if (!isProd) {
          console.log(`cache hit!`)
        }
        return res.end(hit)
      }
    }
  
    const context = {
      title: '{{ name }}', // default title
      url: req.url
    }
    renderer.renderToString(context, (err, html) => {
      if (err) {
        return handleError(err)
      }
      res.end(html)
      if (cacheable) {
        microCache.set(req.url, html)
      }
      if (!isProd) {
        console.log(`whole request: ${Date.now() - s}ms`)
      }
    })
  }
  
  app.get('*', isProd ? render : (req, res) => {
    readyPromise.then(() => render(req, res))
  })
  
  const port = process.env.PORT || {{ port }}
  app.listen(port, '0.0.0.0', () => {
    console.log(`server started at localhost:${port}`)
  })
  