class Nokogiri::XSLT::Stylesheet

def self.parse_stylesheet_doc(document) # :nodoc:
  LibXML.exsltRegisterAll
  generic_exception_handler = lambda do |ctx, msg|
    raise RuntimeError.new(msg) # TODO: varargs
  end
  LibXML.xsltSetGenericErrorFunc(nil, generic_exception_handler)
  ss = LibXML.xsltParseStylesheetDoc(LibXML.xmlCopyDoc(document.cstruct, 1)) # 1 => recursive
  LibXML.xsltSetGenericErrorFunc(nil, nil)
  obj = allocate
  obj.cstruct = LibXML::XsltStylesheet.new(ss)
  obj
end

def apply_to document, params = []
  serialize(transform(document, params))
end

def serialize(document) # :nodoc:
  buf_ptr = FFI::Buffer.new :pointer
  buf_len = FFI::Buffer.new :int
  LibXML.xsltSaveResultToString(buf_ptr, buf_len, document.cstruct, cstruct)
  buf = Nokogiri::LibXML::XmlAlloc.new(buf_ptr.get_pointer(0))
  buf.pointer.read_string(buf_len.get_int(0))
end

def transform(document, params=[]) # :nodoc:
  params = params.to_a.flatten if params.is_a?(Hash)
  raise(TypeError) unless params.is_a?(Array)
  param_arr = FFI::MemoryPointer.new(:pointer, params.length + 1, false)
  # Keep the MemoryPointer instances alive until after the call
  ptrs = params.map { |param | FFI::MemoryPointer.from_string(param.to_s) }
  param_arr.put_array_of_pointer(0, ptrs)
  
  # Terminate the list with a NULL pointer
  param_arr.put_pointer(LibXML.pointer_offset(params.length), nil)
  ptr = LibXML.xsltApplyStylesheet(cstruct, document.cstruct, param_arr)
  raise(RuntimeError, "could not perform xslt transform on document") if ptr.null?
  XML::Document.wrap(ptr)
end