nginx rewrite - one more time

Question

Assuming I've got a rule which looks like this:

RewriteCond %{HTTP_HOST} app_name
RewriteCond %{REQUEST_URI} !^/application/app_name/index.php
RewriteRule .* /application/app_name/index.php/$0 [L]

I've tried to convert it to nginx equivalent but i've failed :-) Here is my implementation (broken)

if (-f $request_filename) {
   break;
}
if (!-f $request_filename) {
   rewrite ^/(.+)$ /application/app_name/index.php?url=$1 last;
   break;
}

Could you guys help?