How to make this with htaccess?

Question

How to make this with htacess:

http://example.com/category => /index.php?action=category
http://example.com/category?query=string => /index.php?action=category&query=string
http://example.com/category/subcategory => /index.php?action=category/subcategory
http://subdomain.example.com => /index.php?action=subdomain
http://subdomain.example.com/category/subcategory => /index.php?action=subdomain/category/subcategory

This is My current code:

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule ^(.*)?$ /index.php?action=$1 [L]

Answer 1

Thanks for helping.

.htaccess code:

RewriteEngine On
RewriteBase /

RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.*)?$ /index.php?action=$1 [L]

index.php code:

$domain = "domain.com";

if($_SERVER["HTTP_HOST"] != $domain)
{
    $subdomain = str_replace(".$domain","",$_SERVER["HTTP_HOST"]);
    $_GET['action'] = (isset($_GET['action'])) ? "$subdomain/".$_GET['action']:$subdomain;
}