How do I setup an .htaccess file to exclude a subdirectory? - .htaccess

Question

I currently have a website setup in the following way:
example.com is the root domain
The .htaccess file redirects all requests to the root URL to blog.example.com
This is because the blog subdomain is a mirror of the main domain and is what will be used moving forward.
The problem is that there's a second domain: product.com that is pointing to example.com/product.
As the .htaccess file is configured, all incoming requests are mapped to blog.example.com.
This means that going to product.com will result in blog.example.com/product in which the ideal scenario is to have example.com/product and all other incoming requests be redirected to blog.example.com.
A copy of my .htaccess file is below:
# Block access to the root site
RewriteCond %{HTTP_HOST} ^(example\.com)$ [NC]
# Whitelist specific areas of the root site
# e.g category slugs or page slugs you want to remain viewable
RewriteCond %{REQUEST_URI} !/blog.* [NC]
RewriteCond %{THE_REQUEST} !/blog.* [NC]
# Set like-to-like redirect URL for anything not whitelisted
RewriteRule (.*) http://blog\.example\.com/$1 [R=301,L]
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
How can I construct my rules in the following way:
product.com redirects to example.com/product
example.com redirects to blog.example.com

Answer 1

This should work:
RewriteEngine On
# redirect anything that is different than /blog and /product to blog.example.com
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteCond %{REQUEST_URI} !/blog.* [NC]
RewriteCond %{REQUEST_URI} !/product.* [NC]
RewriteRule ^(.*)$ http://blog.example.com/$1 [R=301,L]