from typing import TypeVar, Literal, Generic
from typing_extensions import reveal_type

TU = TypeVar('TU', Literal['ms'], Literal['us'])

class Timedelta(Generic[TU]):
  def __init__(self, epoch: int, time_unit: TU) -> None:
    self._epoch = epoch
    self._time_unit = time_unit

  def second(self) -> int:
    m = 1_000 if self._time_unit == 'ms' else 1_000_000
    return self._epoch // m % 60

def convert(nanoseconds: int, time_unit: TU) -> Timedelta[TU]:
  m = 1_000_000 if time_unit == 'ms' else 1_000
  return Timedelta[TU](nanoseconds // m, time_unit)

ns = 1_000_000_000
delta0 = Timedelta[Literal['us']](ns // 1_000, 'us')
delta1 = Timedelta(ns // 1_000, 'us')
delta2 = convert(ns, 'us')

reveal_type(delta0)
reveal_type(delta1)
reveal_type(delta2)