module Nexmo
  module OAS
    module Renderer
      module Helpers
        module Navigation

          HEADING_TAG_DEPTHS = {
            'h0' => 0,
            'h1' => 1,
            'h2' => 2,
            'h3' => 3,
            'h4' => 4,
            'h5' => 5,
            'h6' => 6,
          }.freeze

          def navigation_from_content(content:, title: nil)
            content = "<h0 class='injected'>#{title}</h0>\n" + content if title
            document = build_document(content)

            nodes = ['<ul class="Vlt-sidemenu Vlt-sidemenu--rounded Vlt-sidemenu--flat navigation js-navigation">']
            last_node = nil

            document.css('.reveal').remove

            document.css('h0,h2,h3,h4,h5,h6').each do |heading|
              # If it's a header within tabbed content (including Code Snippets) we don't want to treat
              # the header as a navigation item in the sidebar
              next unless heading.ancestors('.Vlt-tabs').empty?

              # Same with callouts
              next unless heading.ancestors('.Vlt-callout').empty?

              if last_node.nil? || heading.name == last_node.name
                # Do nothing (cleaner than adding wrapping further conditions)
              elsif heading.name >= last_node.name # e.g. h2 -> h3
                nodes << '<ul>'
              else # e.g. h4 -> h2
                (HEADING_TAG_DEPTHS[last_node.name] - HEADING_TAG_DEPTHS[heading.name]).times do
                  nodes << '</li></ul>'
                end
              end

              nodes << <<~HEREDOC
                <li>
                <a class="Vlt-sidemenu__link Vlt-grey-darker" href="##{heading.attributes['id']}" data-scrollspy-id="#{heading['data-id']}">
                  #{heading.text}
                </a>
              HEREDOC
              last_node = heading
            end
            nodes << '</li></ul>'
            nodes.join("\n").html_safe
          end

          private

          def build_document(content)
            Nokogiri::HTML::DocumentFragment.parse(content)
          end

        end
      end
    end
  end
end