Apache mod_rewrite - rewrite to folder name based on %{HTTP_HOST} - infinite loop - apache

Question

I'm currently stuck with an infinite loop problem with mod_rewrite.
What I want (rules to be applied in order):
stript www (redirect)
rewrite request so that the files within the folder named %{HTTP_HOST} (if existent) are used
if the folder doesn't exist, redirect to domain.tld
Examples:
www.subdomain.domain.tld => redirect to subdomain.domain.tld
subdomain.domain.tld => load files within folder named subdomain.domain.tld (and pass the rest of the request)
unknown-subdomain.domain.tld => redirect to domain.tld
What I got so far:
RewriteEngine On
# Store protocol (HTTP or HTTPS) as ENV variable
RewriteCond %{HTTP:CF-Visitor} '"scheme":"http"' [OR]
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ - [env=proto:http]
RewriteCond %{HTTP:CF-Visitor} '"scheme":"https"' [OR]
RewriteCond %{HTTPS} =on
RewriteRule ^(.*)$ - [env=proto:https]
# Stript www
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^ %{ENV:proto}://%1%{REQUEST_URI} [L,NC,QSA,R=301]
# Directory exists => rewrite
RewriteCond %{REQUEST_URI} !^/%{HTTP_HOST} [NC]
RewriteCond %{HTTP_HOST} -d
RewriteRule ^ %{HTTP_HOST}%{REQUEST_URI} [L,NC,QSA]
# Directory doesn't exist => redirect
RewriteCond %{REQUEST_URI} !^/%{HTTP_HOST} [NC]
RewriteCond %{HTTP_HOST} !-d
RewriteRule ^ %{ENV:proto}://domain.tld%{REQUEST_URI} [L,NC,QSA,R]
I know all this can be achieved with virtual hosts. Unfortunately, I'm already on a shared virtual host and .htaccess is all I can make use of, so I'm kinda forced to go that way.
I'm thankful for any help or ideas to lead me to the right direction.

Answer 1

Hope this helps:
RewriteEngine On
RewriteBase "/"
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ - [env=proto:http]
RewriteCond %{HTTPS} =on
RewriteRule ^(.*)$ - [env=proto:https]
# Strip www
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^ %{ENV:proto}://%1%{REQUEST_URI} [L,NC,QSA,R=301]
#Prevent loop
RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule ^ - [L]
# Directory exists => rewrite
RewriteCond %{DOCUMENT_ROOT}/%{HTTP_HOST} -d
RewriteRule ^ /%{HTTP_HOST}%{REQUEST_URI} [L,NC,QSA]
# Directory doesn't exist => redirect (but not if host=example.com)
RewriteCond %{DOCUMENT_ROOT}/%{HTTP_HOST} !-d
RewriteCond %{HTTP_HOST} !=example.com
RewriteRule ^ %{ENV:proto}://example.com%{REQUEST_URI} [L,NC,QSA,R]