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 microcache = require('route-cache')
const resolve = file => path.resolve(__dirname, file)
const { createBundleRenderer } = require('vue-server-renderer')

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()

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, {
        // for component caching
        cache: LRU({
            max: 1000,
            maxAge: 1000 * 60 * 15
        }),
        // this is only needed when vue-server-renderer is npm-linked
        basedir: resolve('./dist'),
        // recommended for performance
        runInNewContext: false
    }))
}

let renderer
let readyPromise
const templatePath = resolve('./index.html')
if (isProd) {
    // In production: create server renderer using template and built server bundle.
    // The server bundle is generated by vue-ssr-webpack-plugin.
    const template = fs.readFileSync(templatePath, 'utf-8')
    const bundle = require('./dist/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('./dist/vue-ssr-client-manifest.json')
    renderer = createRenderer(bundle, {
        template,
        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,
        templatePath,
        (bundle, options) => {
            renderer = createRenderer(bundle, options)
        }
    )
}

const serve = (path, cache) => express.static(resolve(path), {
    maxAge: cache && isProd ? 1000 * 60 * 60 * 24 * 30 : 0
})

app.use(compression({ threshold: 0 }))
app.use('/static', serve('./dist/static', true))

// 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.
// 1-second microcache.
// https://www.nginx.com/blog/benefits-of-microcaching-nginx/
app.use(microcache.cacheSeconds(1, req => useMicroCache && req.originalUrl))

function render(req, res) {
    const s = Date.now()

    res.setHeader("Content-Type", "text/html")
    res.setHeader("Server", serverInfo)

    const handleError = err => {
        if (err.url) {
            res.redirect(err.url)
        } else if (err.code === 404) {
            res.status(404).send('404 | Page Not Found')
        } else {
            // Render Error Page or Redirect
            res.status(500).send('500 | Internal Server Error')
            console.error(`error during render : ${req.url}`)
            console.error(err.stack)
        }
    }

    const context = {
        title: 'Vue HN 2.0', // default title
        url: req.url
    }
    renderer.renderToString(context, (err, html) => {
        if (err) {
            return handleError(err)
        }
        res.send(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 || 8080
app.listen(port, () => {
    console.log(`server started at localhost:${port}`)
})