from Attr import Attr


def objRefJoin(klassId, serialNum):
	""" Given a klass id and object serial number, returns a 64-bit obj ref value (e.g., a long). """
	return (long(klassId)<<32) | long(serialNum)

def objRefSplit(objRef):
	""" Returns a tuple with (klassId, serialNum) given the 64-bit (e.g., long type) objRef. """
	return ((objRef & 0xFFFFFFFF00000000L) >> 32, objRef & 0xFFFFFFFFL)


class ObjRefAttr(Attr):
	"""
	This is an attribute that refers to another user-defined object.
	For a list of objects, use ListAttr.
	"""

	def __init__(self, dict):
		Attr.__init__(self, dict)
		self._className = dict['Type']

	def targetClassName(self):
		""" Returns the name of the base class that this obj ref attribute points to. """
		return self._className

	def targetKlass(self):
		assert self._targetKlass, 'not yet fully initialized'
		return self._targetKlass

	def awakeFromRead(self):
		"""
		Check that the target class actually exists.
		"""
		self._targetKlass = self.model().klass(self.targetClassName(), None)
		if not self._targetKlass:
			from Model import ModelError
			raise ModelError, 'class %s: attr %s: cannot locate target class %s for this obj ref.' % (
				self.klass().name(), self.name(), self.targetClassName())

	def className(self):
		print 'DEPRECATED: ObjRefAttr.className() on 2004-02-27. Use targetClassName() instead.'
		return self.targetClassName()
