RewriteEngine On
RewriteBase /


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


# base domain should use HTTPS
RewriteCond %{HTTPS} off
RewriteCond %{HTTP_HOST} ^[^\.]+\.[^\.]+$
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [L,R=301]


# other domain should use HTTP
RewriteCond %{HTTPS} on
RewriteCond %{HTTP_HOST} !^[^\.]+\.[^\.]+$
RewriteRule ^(.*)$ http://%{HTTP_HOST}/$1 [L,R=301]