jekyll categorize collections

plugin.rb

# frozen_string_literal: true
require "jekyll"

module Jekyll
  class CategorizePageGenerator < Jekyll::Generator
    safe true
    def get_collection(name)
      @site.collections[name] ? @site.collections[name].docs : []
    end

    def add_to_frontmatter(page, values)
      values.each do |key, value|
        # add to the page front matter header
        page.data[key] = value
      end
    end

    def isValid?(item)
      path = item.relative_path.split('/')
      
      # if category folder has no sub categories
      if path.length == 3
        header_values = { "category" => path[1] }
        add_to_frontmatter(item, header_values)
        return false
      end

      return true
    end


    def get_header_values_to_add(item)
      path = item.relative_path.split('/')
      # ignore index.md and index.html files
      if path[1] and path[1] != "index.html" and path[1] != "index.md"
        category = path[1]
      end
      if path[2] and path[2] != "index.html" and path[2] != "index.md"
        sub_category = path[2]
      end
      
      return {
        "category" => category,
        "sub_category" => sub_category
      }
    end

    # main generator init function
    def generate(site)
      @site = site
      # The collections to add category/sub category front matter values
      # IMPORTANT: specify collection in _data/categorize_collection.yml
      # or defaults to pages collection       
      collections = @site.data["categorize_collections"] || ["pages"]

      for c in collections
        for item in get_collection(c)
          valid_category = isValid?(item)
          if valid_category
            header_values = get_header_values_to_add(item)
            add_to_frontmatter(item, header_values)
          end
        end
      end
    end

  end
end