module Nokogiri::LibXML::XmlDocumentMixin

def self.included(base)
  base.class_eval do
    layout(
      :_private,  :pointer,
      :type,      :int,
      :name,      :string,
      :children,  :pointer,
      :last,      :pointer,
      :parent,    :pointer,
      :next,      :pointer,
      :prev,      :pointer,
      :doc,       :pointer,
      :compression,       :int,
      :standalone,        :int,
      :intSubset,         :pointer,
      :extSubset,         :pointer,
      :oldNs,             :pointer,
      :version,           :string,
      :encoding,          :pointer,
      :ids,               :pointer,
      :refs,              :pointer,
      :URL,               :string
      )
  end
end

def alloc_tuple
  self[:_private] = LibXML.calloc(FFI.type_size(:pointer), 2)
  self[:_private].put_pointer(FFI.type_size(:pointer), LibXML.xmlXPathNodeSetCreate(nil))
end

def document
  p = self[:doc]
  p.null? ? nil : LibXML::XmlDocumentCast.new(p)
end

def ruby_doc
  ptr = self[:_private]
  return nil if ptr.null?
  ObjectSpace._id2ref(ptr.get_long(0))
end

def ruby_doc=(object)
  self[:_private].put_long(0, object.object_id)
end

def unlinked_nodes
  LibXML::XmlNodeSetCast.new(self[:_private].get_pointer(FFI.type_size(:pointer)))
end