let of_sec s =
  Unix.gmtime s

let to_sec t =
  let sec  = t.Unix.tm_sec
  and min  = t.Unix.tm_min
  and hour = t.Unix.tm_hour
  and mday = t.Unix.tm_mday
  in
  sec +
  min  * 60 +
  hour * 60 * 60 + 
  mday * 60 * 60 * 24 

let string_of_t t = 
  let mday = t.Unix.tm_mday in
  let sec  = t.Unix.tm_sec
  and min  = t.Unix.tm_min
  and hour = t.Unix.tm_hour + 24*mday
  in
  Printf.sprintf "%2d:%2d:%2d" hour min sec

let string_of_sec s = 
  of_sec s 
  |> string_of_t