server.php

<?php
$scriptInvokedFromCli =
 isset($_SERVER['argv'][0]) && $_SERVER['argv'][0] === 'server.php';

if($scriptInvokedFromCli) {
 $port = getenv('PORT');
 if (empty($port)) {
 $port = "3000";
 }

 echo 'starting server on port '. $port . PHP_EOL;
 exec('php -S localhost:'. $port . ' -t public server.php');
} else {
 return routeRequest();
}

function routeRequest()
{
 $comments = file_get_contents('comments.json');
 switch($_SERVER["REQUEST_URI"]) {
 case '/':
 echo file_get_contents('./public/index.html');
 break;
 case '/comments.json':
 if($_SERVER['REQUEST_METHOD'] === 'POST') {
 $commentsDecoded = json_decode($comments, true);
 $commentsDecoded[] = ['author' => $_POST['author'],
 'text' => $_POST['text']];

 $comments = json_encode($commentsDecoded, JSON_PRETTY_PRINT);
 file_put_contents('comments.json', $comments);
 }
 header('Content-Type: application/json');
 header('Cache-Control: no-cache');
 echo $comments;
 break;
 default:
 return false;
 }
}