app.js

/**
 * Copyright 2015-2016, Google, Inc.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

const express = require('express');
const app = express();
const useragent = require('useragent');

const BASE_FILE_PATH  = __dirname + '/public';

app.get('/articles/article-:id.html', (req, res) => {
  if (useragent.is(req.headers['user-agent']).safari && req.query.shell !== 'false') {
    // Serve appshell
    res.sendFile(BASE_FILE_PATH + '/shell.html');    
  } else {
    // Serve AMP!
    res.sendFile(BASE_FILE_PATH + '/articles/article-' + req.params.id + '.html');        
  }
});

app.use(express.static('public'));

const port = process.env.PORT || 3000;
app.listen(port, () => {
  console.log('Example app listening on port 3000!')
});