t: let
  rem = x: y: x - x / y * y;
  days = t / 86400;
  secondsInDay = rem t 86400;
  hours = secondsInDay / 3600;
  minutes = (rem secondsInDay 3600) / 60;

  # Courtesy of https://stackoverflow.com/a/32158604.
  z = days + 719468;
  era =
    (
      if z >= 0
      then z
      else z - 146096
    )
    / 146097;
  doe = z - era * 146097;
  yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
  y = yoe + era * 400;
  doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
  mp = (5 * doy + 2) / 153;
  d = doy - (153 * mp + 2) / 5 + 1;
  m =
    mp
    + (
      if mp < 10
      then 3
      else -9
    );
  y' =
    y
    + (
      if m <= 2
      then 1
      else 0
    );

  pad = s:
    if builtins.stringLength s < 2
    then "0" + s
    else s;
in "${toString y'}-${pad (toString m)}-${pad (toString d)}-${pad (toString hours)}:${pad (toString minutes)}"