class Nokogiri::CSS::XPathVisitor

def accept node
  node.accept(self)
end

def is_of_type_pseudo_class? node
  if node.type==:PSEUDO_CLASS
    if node.value[0].is_a?(Nokogiri::CSS::Node) and node.value[0].type == :FUNCTION
      node.value[0].value[0]
    else
      node.value[0]
    end =~ /(nth|first|last|only)-of-type(\()?/
  end   
end

def nth node, options={}
  raise ArgumentError, "expected an+b node to contain 4 tokens, but is #{node.value.inspect}" unless node.value.size == 4
  a, b = read_a_and_positive_b node.value
  position = if options[:child]
    options[:last] ? "(count(following-sibling::*) + 1)" : "(count(preceding-sibling::*) + 1)"
  else
    options[:last] ? "(last()-position()+1)" : "position()"
  end
  if b.zero?
    "(#{position} mod #{a}) = 0"
  else
    compare = a < 0 ? "<=" : ">="
    if a.abs == 1
      "#{position} #{compare} #{b}"
    else
      "(#{position} #{compare} #{b}) and (((#{position}-#{b}) mod #{a.abs}) = 0)"
    end
  end
end

def read_a_and_positive_b values
  op = values[2]
  if op == "+"
    a = values[0].to_i
    b = values[3].to_i
  elsif op == "-"
    a = values[0].to_i
    b = a - (values[3].to_i % a)
  else
    raise ArgumentError, "expected an+b node to have either + or - as the operator, but is #{op.inspect}"
  end
  [a, b]
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(' ', normalize-space(@class), ' '), ' #{node.value.first} ')"
end

def visit_combinator node
  if is_of_type_pseudo_class?(node.value.last)
    "#{node.value.first.accept(self) if node.value.first}][#{node.value.last.accept(self)}"
  else
    "#{node.value.first.accept(self) if node.value.first} and #{node.value.last.accept(self)}"
  end
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
  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)\(/
    if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :NTH
      nth(node.value[1])
    else
      "position() = #{node.value[1]}"
    end
  when /^nth-child\(/
    if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :NTH
      nth(node.value[1], :child => true)
    else
      "count(preceding-sibling::*) = #{node.value[1].to_i-1}"
    end
  when /^nth-last-of-type\(/
    if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :NTH
      nth(node.value[1], :last => true)
    else
      index = node.value[1].to_i - 1
      index == 0 ? "position() = last()" : "position() = last() - #{index}"
    end
  when /^nth-last-child\(/
    if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :NTH
      nth(node.value[1], :last => true, :child => true)
    else
      "count(following-sibling::*) = #{node.value[1].to_i-1}"
    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" then "position() = 1"
    when "first-child" then "count(preceding-sibling::*) = 0"
    when "last" then "position() = last()"
    when "last-child" then "count(following-sibling::*) = 0"
    when "first-of-type" then "position() = 1"
    when "last-of-type" then "position() = last()"
    when "only-child" then "count(preceding-sibling::*) = 0 and count(following-sibling::*) = 0"
    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