htaccess list directory and rewrite rules for it

I'm trying to make a .htaccess code for automatically rewrite rules for a directory. In example:

URL: https://example.com/assets/test.png
Folder: /src/assets/test.png

or,

URL: https://example.com/js/test.js
Folder: /src/js/test.js

My htaccess file:

#Rewrite to www
RewriteEngine On
RewriteCond %{HTTP_HOST} ^[^.]+\.[^.]+$
RewriteRule ^(.*)$ https://www.%{HTTP_HOST}/$1 [L,R=301]

#remove html file extension
RewriteEngine on 
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html [NC,L]

#remove php file extension
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^(.*)$ $1.php [NC,L] 

How can i make this?