server.js

const express = require("express")
const path = require("path")
const { existsSync } = require("fs-extra")
const { getEnvironments, getEnvConfiguration } = require("./client-helpers/environment-helpers")
const argv = require("optimist").argv

// ssg configuration based on environment
let staticDir = ""
let entryPointDir = ""
let envConfiguration = null

const sendFileOr404 = (req, res, reqPath) => {
  const dest = path.join(process.cwd(), reqPath)

  if (existsSync(dest)) {
    res.sendFile(dest)
  } else {
    res.status(404)
    res.sendFile(path.join(process.cwd(), staticDir, "/404/index.html"))
  }
}

module.exports = async function main(options) {
  const environments = await getEnvironments()
  const app = express()
  const defaultEnvironment = await require("./jsdom-ssg/flags/get-ssg-environment")(options.environment)
  const serverMode = await require("./jsdom-ssg/flags/get-server-mode")(options.serverMode)
  await setEnvDirs(defaultEnvironment, serverMode)

  app.get("/*", async function (req, res) {
    const reqPath = req.path

    // Handle files that are local (node_modules, etc) by checking for file extensions (".")
    if (reqPath.indexOf(".") !== -1) {
      // Simulate hosting all assets, bundles at one directory inside the dist directory
      if (envConfiguration.serveFromDist) {
        sendFileOr404(req, res, path.join(staticDir, reqPath))
        return
      }

      // Serve static files from dist, but assets, node_modules/bundles are loaded outside of dist
      sendFileOr404(req, res, reqPath)

      return
    }

    if (serverMode === "spa") {
      sendFileOr404(req, res, entryPointDir)
      return
    }

    // Host static files
    if (serverMode === "ssg") {
      sendFileOr404(req, res, path.join(staticDir, reqPath, "index.html"))
      return
    }
  })

  // Handle 404 - Keep this as a last route
  app.use(function (req, res, next) {
    res.status(404)
    res.send("404: File Not Found")
  })

  app.listen(argv.port || 8080, function () {
    console.log("Example app listening on port " + argv.port || 8080)
  })
}

/**
 * Gets environment configuration and overrides global configurations for server
 */
async function setEnvDirs(environment, serverMode) {
  const configuration = await getEnvConfiguration(environment)
  envConfiguration = configuration

  const basePath = path.join("dist", configuration.dist.basePath)

  staticDir = path.join(basePath, envConfiguration.dist.static)
  entryPointDir = envConfiguration.serveFromDist ? path.join(basePath, envConfiguration.dist.entryPoint) : envConfiguration.entryPoint

  console.log("server environment:", environment, "mode:", serverMode)
}