htmldoc.rb

class HTMLDoc
  def initialize
    @node_id = 0
    @parent_id = 0
    @doc = []

    yield self if block_given?
  end

  def el(type, attributes = {})
    @node_id += 1
    grandparent_id = @parent_id

    node = {
      id: @node_id,
      parent_id: @parent_id,
      type: type,
      attrs: attributes
    }

    case type
    when :text
      @doc << node.merge(content: yield)
    else
      @doc << node
      @parent_id = @node_id
      
      yield
    end

    @parent_id = grandparent_id
  end

  def ast
    root = @doc.find {|el| el[:parent_id] == 0 }
    { type: root[:type],
      attributes: root[:attrs],
      children: gather_children(root[:id])
    }
  end

  def gather_children(node_id)
    @doc.select do |el|
      el[:parent_id] == node_id
    end.map do |el|
      if el[:type] == :text
        children = [el[:content]]
      else
        children = gather_children(el[:id])
      end

      { type: el[:type],
        attributes: el[:attrs],
        children: children }
    end
  end

  def to_s
    puts @doc.inspect # DEBUG
    puts ast.inspect  # DEBUG
    node(ast[:type], ast[:attributes], ast[:children])
  end

  def node(type, attributes = {}, children = [])
    case type
    when :text
      children.empty? ? "" : children.first
    when :input
      render_opening_tag(type, attributes)
    else
      [
        render_opening_tag(type, attributes), 
        render_children(children), 
        "</#{type}>"
      ].flatten.join("\n")
    end
  end

  def render_children(children)
    children.map do |child|
      node(child[:type], child[:attributes], child[:children])
    end.flatten.join("\n")
  end

  def render_opening_tag(name, attrs)
    if attrs.nil? || attrs.empty?
      "<#{name}>"
    else
      "<#{name} #{stringify_attrs(attrs)}>"
    end
  end

  def stringify_attrs(attrs)
    attrs.map do |key, value|
      %Q(#{key}="#{value}")
    end.join(" ")
  end
end

doc = HTMLDoc.new do |d|
  d.el :html do
    d.el :head do
      d.el :title do
        d.el :text do
          "Hello,"
        end
        d.el :text do
          " World!"
        end
      end
    end
    d.el :body do
      d.el :h1 do
        d.el :text do
          "TITLE"
        end
      end
      d.el :p do
        d.el :text do
          "Paragraph 1"
        end
      end
      d.el :p do
        d.el :text do
          "Paragraph 2"
        end
      end
    end
  end
end

puts doc.to_s