type t = Ptime.t option
type span = Ptime.Span.t option

let diff a b =
  match (a, b) with
  | None, _ | _, None -> None
  | Some a, Some b -> Some (Ptime.diff a b)

let add_span_exn t span =
  match (t, span) with
  | None, _ | _, None -> None
  | Some t, Some span -> (
      match Ptime.add_span t span with
      | None -> Fmt.failwith "add_span_exn: not in the range [min;max]"
      | Some v -> Some v)

let of_span_exn = function
  | None -> None
  | Some span -> (
      match Ptime.of_span span with
      | None -> Fmt.failwith "of_span_exn: not in the range [min;max]"
      | Some p -> Some p)

(* -- *)

(* 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

(* TODO exn *)
let ptime_to_int64 ptime = ptime |> Ptime.to_float_s |> Int64.of_float

let ptime_of_int64 i =
  match Ptime.of_float_s (Int64.to_float i) with
  | None -> Fmt.failwith "ptime_of_int64 error: `%Ld` is not a valid ptime" i
  | Some ts -> ts

let encode_int64 = function None -> Int64.max_int | Some p -> ptime_to_int64 p
let decode_int64 i = if i = Int64.max_int then None else Some (ptime_of_int64 i)

(* 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