Jekyll Liquid sub-navigation not properly selecting - jekyll

Question

I'm building a static website on gh-pages using jekyll liquid. I'm properly generating a simple, two-level navigation from a data file. My problem is that I am stuck trying to do two things:
Apply a "selected" class to the current page link item.
Apply an "open" class to the parent list item when a sublink menu is present.
Here's the format I'm using in my _data/nav.yml file
- title: Top Level Nav Item
url: level-1/
sublinks:
- title: Child Nav Item 1
url: child-1/
- title: Child Nav Item 2
url: child-2/
Here's how I'm building my navigation:
{% assign current_page = page.url | remove: 'index.html' %}
<ul class="-nav">
{% for nav in include.nav %}
{% assign current = null %}
{% if nav.url == current_page %}
{% assign current = ' _selected' %}
{% endif %}
{% if nav.url contains current_page %}
{% assign open = ' _open' %}
{% endif %}
<li class="-item{{ current }}{{ open }}">
{{ nav.title }}
{% if nav.sublinks and current_page contains nav.url %}
{% include navigation.html nav=nav.sublinks%}
{% endif %}
</li>
{% endfor %}
</ul>
Again this builds my navigation correctly, but it doesn't apply either the selected or open class.
Here's what I'm would like it to look like in the end:
What am I doing wrong?

Answer 1

Finally got this working. I solved it by adding an item to the front matter of my page called permalink where I specified the desired page permalink.
---
layout: default
title: Example
permalink: url/example/
---
I use this permalink to check against the current page.url to add the desired _selected class on the <li> element.
I made one modification to my example data file, adding in the parent url_part into the child's url. I'm not sure why, but I had trouble printing the entire URL correctly otherwise.
- title: Top Level Nav Item
url: level-1/
sublinks:
- title: Child Nav Item 1
url: level-1/child-1/
- title: Child Nav Item 2
url: level-1/child-2/
Lastly for my navigation.html include, here's how I'm creating my main menu, rendering sub-menus if they exist and should be shown, and properly selecting the active link:
{% assign current_page = page.url | remove: 'index.html' %}
<ul class="-nav">
{% for nav in include.nav %}
{% assign current = null %}
{% if nav.url == page.permalink %}
{% assign current = ' _selected' %}
{% endif %}
<li class="-item{{ current }}">
{{ nav.title }}
{% if nav.sublinks and current_page contains nav.url %}
{% include navigation.html nav=nav.sublinks%}
{% endif %}
</li>
{% endfor %}
</ul>
The big difference between this and the snippet I originally posted is I dropped the {{ open }} stuff for now. One problem at a time. The other thing is that I'm checking to see if nav.url equals page.permalink. Before I was checking against page.url and this always failed for me.
It's probably not the prettiest, but I finally got a jekyll liquid menu to generate (semi-)dynamically and properly select the active link.