{%- comment -%}
  Generate image final URL based on `site.img_cdn`, `page.img_path`

  Arguments:
    src - basic image path, required
    img_path - relative path of image, optional

  Return:
    image URL
{%- endcomment -%}

{% assign url = include.src %}

{%- if url -%}
  {%- comment -%} CND URL {%- endcomment -%}
  {% assign prefix = site.img_cdn | default: '' | relative_url %}

  {%- comment -%} Add page image path prefix {%- endcomment -%}
  {% assign url = include.img_path | default: '' | append: '/' | append: url %}

  {% assign url = prefix | append: '/' | append: url | replace: '///', '/' | replace: '//', '/' | replace: ':', ':/' %}
{%- endif -%}

{{- url -}}