dateSort = (date_a, date_b) ->
  if date_a
    a = if date_a.toISOString then date_a.toISOString() else date_a
  else
    a = null
  if date_b
    b = if date_b.toISOString then date_b.toISOString() else date_b
  else
    b = null
  Ember.compare a, b

create_date_sort = (attribute) ->
  (object_a, object_b) ->
    dateSort object_a.get(attribute), object_b.get(attribute)
export { create_date_sort }
export default dateSort