paginateQuery :: Pagination -> Query a -> Query a
paginateQuery (Pagination p w) = limit p . offset ((p-1) * w)

paginate
  :: (CanOpaleye c e m, Default QueryRunner a b)
  => Pagination
  -> (a -> Column i)
  -> Query a
  -> m (PaginationResults b)
paginate p getId q = do
  res <- liftQuery $ paginateQuery p q
  c   <- liftQueryFirst . aggregate count . fmap getId $ q
  return $ PaginationResults
    (p^.paginationPage)
    (p^.paginationWidth)
    (fromMaybe 0 c)
    res