htaccess rewrite with subdomain as variable - php

Question

I have a sitename.net and in a root directory i have .htaccess and index.php
.htaccess is:
FallbackResource /index.php
so basically as it's empty site (no sub directories, no files etc...) I will get a fallback to index.php which contains this:
$path = ltrim($_SERVER['REQUEST_URI'], '/'); // Trim leading slash(es)
$elements = explode('/', $path); // Split path on slashes
echo "Domain is: $domain <br>";
if(empty($elements[0])) { // No path elements means home
echo "ShowHomepage()";
}
else switch(array_shift($elements)) { // Pop off first item and switch
case 'tests':
echo "First is test";
case 'sample':
echo "First is sample";
default:
header('HTTP/1.1 404 Not Found');
Show404Error();
}
my problem is that when visitor enters: https://username.sitename.net/tests/test1
I get error as subdomain doesn't exist...
When I go to "https://sitename.net/tests/test1" i get what I want but I need username as a variable as well.
Should I first do rewrite in .htaccess so it translate https://username.sitename.net/tests/test1 as https://sitename.net/username/tests/test1 and than redo index.php so it pickup a first array element as username or there is another option ?
Can somebody help me out ?
------------- EDIT ----------------
I've ended up pointing A record *.sitename.net to server IP
I've changed .htaccess so it's:
RewriteEngine on
RewriteBase /
RewriteCond %{HTTP_HOST} ^(.*)\.sitename\.net
RewriteRule ^(.*)$ subdomains/%1/$1 [L,NC,QSA]
FallbackResource /index.php
...and still getting 404 error... still can't get:
https://username.sitename.net/tests/test1 to act like https://sitename.net/username/tests/test1 so index.php will do it stuff...

Answer 1

I think wildcard DNS records is what you're looking for.
https://en.wikipedia.org/wiki/Wildcard_DNS_record
All subdomains will then redirect to your DNS, which you can redirect to your server.
EDIT:
Once the subdomains are up and running, you can use
.htaccess rewrite subdomain to directory
to fix the htaccess.

Answer 2

This work with php redirect too:
$url = "https://gbr8295.sitename.net"; //$_SERVER['HTTP_HOST']
if (substr($_SERVER['HTTP_HOST'], 0, 16) != 'https://sitename') { // You need edit 16 to a correct number for your domain
$username = substr($url, 8, ((strpos($url, '.') - 8)));
$new_url = "https://sitename.net/".$username."/";
echo $url."<br>"; // Output: https://gbr8295.sitename.net
echo $new_url; // Output: https://sitename.net/gbr8295/
header("Location: $new_url");
exit;
} else {
echo 'ok';
}