class Nokogiri::CSS::XPathVisitor

def accept node
  node.accept(self)
end

def an_plus_b node, options={}
  raise ArgumentError, "expected an+b node to contain 4 tokens, but is #{node.value.inspect}" unless node.value.size == 4
  a = node.value[0].to_i
  b = node.value[3].to_i
  position = options[:last] ? "(last()-position()+1)" : "position()"
  if (b == 0)
    return "(#{position} mod #{a}) = 0"
  else
    compare = (a < 0) ? "<=" : ">="
    return "(#{position} #{compare} #{b}) and (((#{position}-#{b}) mod #{a.abs}) = 0)"
  end
end

def visit_attribute_condition node
   attribute = if (node.value.first.type == :FUNCTION) or (node.value.first.value.first =~ /::/)
                 ''
               else
                 '@'
               end
  attribute += node.value.first.accept(self)
  # Support non-standard css
  attribute.gsub!(/^@@/, '@')
  return attribute unless node.value.length == 3
  value = node.value.last
  value = "'#{value}'" if value !~ /^['"]/
  case node.value[1]
  when :equal
    attribute + " = " + "#{value}"
  when :not_equal
    attribute + " != " + "#{value}"
  when :substring_match
    "contains(#{attribute}, #{value})"
  when :prefix_match
    "starts-with(#{attribute}, #{value})"
  when :dash_match
    "#{attribute} = #{value} or starts-with(#{attribute}, concat(#{value}, '-'))"
  when :includes
    "contains(concat(\" \", #{attribute}, \" \"),concat(\" \", #{value}, \" \"))"
  when :suffix_match
    "substring(#{attribute}, string-length(#{attribute}) - " +
      "string-length(#{value}) + 1, string-length(#{value})) = #{value}"
  else
    attribute + " #{node.value[1]} " + "#{value}"
  end
end

def visit_class_condition node
  "contains(concat(' ', @class, ' '), ' #{node.value.first} ')"
end

def visit_conditional_selector node
  node.value.first.accept(self) + '[' +
  node.value.last.accept(self) + ']'
end

def visit_element_name node
  node.value.first
end

def visit_function node
  #  note that nth-child and nth-last-child are preprocessed in css/node.rb.
  msg = :"visit_function_#{node.value.first.gsub(/[(]/, '')}"
  return self.send(msg, node) if self.respond_to?(msg)
  case node.value.first
  when /^text\(/
    'child::text()'
  when /^self\(/
    "self::#{node.value[1]}"
  when /^eq\(/
    "position() = #{node.value[1]}"
  when /^(nth|nth-of-type|nth-child)\(/
    if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :AN_PLUS_B
      an_plus_b(node.value[1])
    else
      "position() = #{node.value[1]}"
    end
  when /^(nth-last-child|nth-last-of-type)\(/
    if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :AN_PLUS_B
      an_plus_b(node.value[1], :last => true)
    else
      index = node.value[1].to_i - 1
      index == 0 ? "position() = last()" : "position() = last() - #{index}"
    end
  when /^(first|first-of-type)\(/
    "position() = 1"
  when /^(last|last-of-type)\(/
    "position() = last()"
  when /^contains\(/
    "contains(., #{node.value[1]})"
  when /^gt\(/
    "position() > #{node.value[1]}"
  when /^only-child\(/
    "last() = 1"
  when /^comment\(/
    "comment()"
  when /^has\(/
    node.value[1].accept(self)
  else
    args = ['.'] + node.value[1..-1]
    "#{node.value.first}#{args.join(', ')})"
  end
end

def visit_id node
  node.value.first =~ /^#(.*)$/
  "@id = '#{$1}'"
end

def visit_not node
  child = node.value.first
  if :ELEMENT_NAME == child.type
    "not(self::#{child.accept(self)})"
  else
    "not(#{child.accept(self)})"
  end
end

def visit_pseudo_class node
  if node.value.first.is_a?(Nokogiri::CSS::Node) and node.value.first.type == :FUNCTION
    node.value.first.accept(self)
  else
    msg = :"visit_pseudo_class_#{node.value.first.gsub(/[(]/, '')}"
    return self.send(msg, node) if self.respond_to?(msg)
    case node.value.first
    when "first", "first-child" then "position() = 1"
    when "last", "last-child" then "position() = last()"
    when "first-of-type" then "position() = 1"
    when "last-of-type" then "position() = last()"
    when "only-of-type" then "last() = 1"
    when "empty" then "not(node())"
    when "parent" then "node()"
    when "root" then "not(parent::*)"
    else
      node.value.first + "(.)"
    end
  end
end