base_path.html

{%- comment -%}
When the website is built by GitHub Pages,
'site.url' is set to 'https://username.github.io'
'site.baseurl' is set to '/lesson-name'

When we start a local server using `jekyll serve`,
'site.url' is set to 'http://localhost:4000' and
'site.baseurl' is empty.

In both of the above cases we set 'relative_root_path' to 'site.baseurl'.

When we build a website locally with `jekyll build`,
both 'site.url' and 'site.baseurl' are empty.
This case is handled by the last 'else' in the code below.
The logic there follows the (adapted) instructions found at:
    https://ricostacruz.com/til/relative-paths-in-jekyll

    `page.url` gives the URL of the current page with a leading /:

    - when the URL ends with an extension (e.g., /foo/bar.html),
      we can get the 'depth' of the page by counting the number of
      forward slashes ('/') and subtracting 1
    - when the URL ends with a forward slash (e.g. /foo/bar/),
      we can get the depth of the page by counting the number of /
{%- endcomment -%}

{% if site.url %}
  {% assign relative_root_path = site.baseurl %}
{% else %}
  {% assign last_char = page.url | slice: -1 %}
  {% if last_char == "/" %}
    {% assign offset = 0 %}
  {% else %}
    {% assign offset = 1 %}
  {% endif %}
  {% assign depth = page.url | split: '/' | size | minus: offset %}
  {% if    depth <= 1 %}{% assign relative_root_path = '.' %}
  {% elsif depth == 2 %}{% assign relative_root_path = '..' %}
  {% else %}{% capture relative_root_path %}..{% for i in (3..depth) %}/..{% endfor %}{% endcapture %}
  {% endif %}
{% endif %}