class Nokogiri::CSS::Node

def accept visitor
  visitor.send(:"visit_#{type.to_s.downcase}", self)
end

def find_by_type(types)
  matches = []
  matches << self if to_type == types
  @value.each do |v|
    matches += v.find_by_type(types) if v.respond_to?(:find_by_type)
  end
  matches
end

def initialize type, value
  @type = type
  @value = value
end

def preprocess!
  ### Deal with nth-child
  matches = find_by_type(
    [:CONDITIONAL_SELECTOR,
      [:ELEMENT_NAME],
      [:PSEUDO_CLASS,
        [:FUNCTION]
      ]
    ]
  )
  matches.each do |match|
    if match.value[1].value[0].value[0] =~ /^nth-child/
      tag_name = match.value[0].value.first
      match.value[0].value = ['*']
      match.value[1] = Node.new(:COMBINATOR, [
        match.value[1].value[0],
        Node.new(:FUNCTION, ['self(', tag_name])
      ])
    end
    if match.value[1].value[0].value[0] =~ /^nth-last-child/
      tag_name = match.value[0].value.first
      match.value[0].value = ['*']
      match.value[1] = Node.new(:COMBINATOR, [
        match.value[1].value[0],
        Node.new(:FUNCTION, ['self(', tag_name])
      ])
    end
  end
  ### Deal with first-child, last-child
  matches = find_by_type(
    [:CONDITIONAL_SELECTOR,
      [:ELEMENT_NAME], [:PSEUDO_CLASS]
  ])
  matches.each do |match|
    if ['first-child', 'last-child'].include?(match.value[1].value.first)
      which = match.value[1].value.first.gsub(/-\w*$/, '')
      tag_name = match.value[0].value.first
      match.value[0].value = ['*']
      match.value[1] = Node.new(:COMBINATOR, [
        Node.new(:FUNCTION, ["#{which}("]),
        Node.new(:FUNCTION, ['self(', tag_name])
      ])
    elsif 'only-child' == match.value[1].value.first
      tag_name = match.value[0].value.first
      match.value[0].value = ['*']
      match.value[1] = Node.new(:COMBINATOR, [
        Node.new(:FUNCTION, ["#{match.value[1].value.first}("]),
        Node.new(:FUNCTION, ['self(', tag_name])
      ])                                        
    end
  end
  self
end

def to_a
  [@type] + @value.map { |n| n.respond_to?(:to_a) ? n.to_a : [n] }
end

def to_type
  [@type] + @value.map { |n|
    n.to_type if n.respond_to?(:to_type)
  }.compact
end

def to_xpath prefix = '//', visitor = XPathVisitor.new
  self.preprocess!
  prefix + visitor.accept(self)
end