htaccess rewrite folder with category name and post url

I would like to be able to rewrite the url on my webpage so it also includes a category.

What I want is the URL to look something like this.

mypage.com/blog/category_name/post_url

What I have now is a folder called blog where I have an .htaccess file but I don't really understand how to use the variables to create something like above example. This is what I have right now. my post details page is located inside blog folder.

My current url to access

mypage.com/blog/post_details.php?post_id=post_url&category_name=ABC

so the final url should look like

mypage.com/blog/ABC/post_url