type t = int64 option
type span = t

let never = -1L
let of_uint64_us us = if us = never then None else Some us
let to_uint64_us = function None -> never | Some us -> us

let to_s us =
  if us = never then None
  else
    let s = Int64.unsigned_div us 86_400_L in
    Some s

module Span = struct
  type t = span

  let of_uint64_us = of_uint64_us
  let to_uint64_us = to_uint64_us
  let to_s = to_s
end

let compare = Int64.unsigned_compare

let now () =
  let d, ps = Ptime_clock.now () |> Ptime.to_span |> Ptime.Span.to_d_ps in
  if d < 0 then Fmt.failwith "Ptime_clock.now negative ptime"
  else
    let d = Int64.(mul (of_int d) 86_400_L) in
    let us = Int64.(div ps 1_000_000_L) in
    Int64.add d us

let add_span t span =
  let us = Int64.add t span in
  if compare t us > 0 then None else Some us

let sub_span t span =
  let us = Int64.sub t span in
  if compare t us < 0 then None else Some us

let diff a b = if compare a b < 0 then None else Some (Int64.sub a b)
(*
(* microseconds since the UNIX Epoch, or "never" if None *)
let jsont =
  let number_or_never_jsont =
    let never =
      let dec s =
        match s with
        | "never" -> None
        | _ -> Jsont.Error.msg Jsont.Meta.none "unexpected string value"
      in
      let enc = function None -> "never" | _ -> assert false in
      Jsont.map ~dec ~enc Jsont.string
    in
    let number =
      let dec n = Ptime.of_float_s n in
      let enc = function Some n -> Ptime.to_float_s n | _ -> assert false in
      Jsont.map ~dec ~enc Jsont.number
    in
    let enc = function None -> never | Some _ -> number in
    Jsont.any ~dec_string:never ~dec_number:number ~enc ()
  in
  let make t = t in
  Jsont.Object.map ~kind:"Timestamp" make
  |> Jsont.Object.mem "t_s" number_or_never_jsont ~enc:Fun.id
  |> Jsont.Object.finish

(* UINT64_MAX represents "never". *)
let bin = Bin.map Bin.neint64 decode_int64 encode_int64
let bin_nbo = Bin.map Bin.beint64 decode_int64 encode_int64

let caqti : Ptime.t option Caqti_type.t =
  let encode v = Ok (encode_int64 v) in
  let decode v = Ok (decode_int64 v) in
  Caqti_type.custom ~encode ~decode Caqti_type.int64
  *)