Nanoc::Filter.define(:tufte) do |content, params|
  doc = Nokogiri::HTML.fragment(content)

  # Convert to array to avoid modifying during iteration
  nodes = doc.children.to_a
  
  # Track the current section we're building
  current_section = nil
  
  # Process each node
  nodes.each do |node|
    if node.name == 'h2'
      # Start a new section
      current_section = Nokogiri::XML::Node.new('section', doc)
      node.add_previous_sibling(current_section)
      current_section.add_child(node)
    elsif current_section && node.name != 'h2'
      # Add this node to the current section
      current_section.add_child(node)
    end
  end

  doc.to_html.gsub(/\[\^([^\]]+)\]:\s*(.+)$/) do |match|
    ref = $1
    note_content = $2.strip
    "<span class=\"sidenote\">#{note_content}</span>"
  end
end