dom.rb

class Generator
  class Tag
    attr_accessort :name, :children, :level
    def initialize(name, level = 0, &block)
      @name = name
      @level = level
      @children = []
      instance_eval(&block)
    end

    def to_html
      [
        shift + "<#{name}>",
        children.map(&:to_html),
        shift + "</#{name}>",
      ].join("\n")
    end

    def shift
      "  " * level
    end

    def tag(name, &block)
      @children << Tag.new(name, level + 1, &block)
    end

    def text(string)
      @children << Text.new(string, level + 1)
    end

    def change(*names, &block)
      if names.empty?
        @children = []
        instance_eval(&block)
        return true
      else
        return @children.any? do |child|
          if child.is_a?(Tag)
            child.change(names[1..-1], &block)
          end
        end
      end
    end
  end

  class Text
    attr_accessort :string

    def to_html
      string
    end
  end

  def html(&block)
    Tag.new('html', &block).to_html
  end

end