Using frontmatter blog article data with `proxy` in the config step

Hi!

I’m currently migrating a blog from Refinery-blog to middleman-blog. Exporting the data to middleman from refinery and I want to create an index page for each category. Currently category is added as a frontmatter in each blog post article, like so:

---
category: Salud
---

What I want is /category/salud.html to list the blog posts that belong to this category. Apparently middleman-blog doesn’t have this feature built-in (categories index - please let me know if it’s possible outside the box). I tried to use the dynamic pages (the proxy method) to generate the pages:

blog_categories.each do |name, articles|
  proxy "/categories/#{name}.html", "category.html", :locals => { :articles => articles }
end

blog_categories is custom method defined in a helper, and it basically builds a list of categories based off blog.articles and filters the corresponding articles for each cat, adding them to a Hash of cat => list of articles. It works great if called from a template, but fails on config.rb because blog is undefined at this moment.

I’m a bit lost on how to accomplish this. Any hints would be much appreciated!

Thanks.