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(* Open Source License                                                       *)
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type error += Invalid_slot of int

let () =
  register_error_kind
    `Permanent
    ~id:"slot.invalid_slot"
    ~title:"invalid slot"
    ~description:"Invalid slot"
    ~pp:(fun ppf x -> Format.fprintf ppf "invalid slot: %d" x)
    Data_encoding.(obj1 (req "bad_slot" int31))
    (function Invalid_slot x -> Some x | _ -> None)
    (fun x -> Invalid_slot x)

include Compare.Int

type slot = t

(* TODO? should there be some assertions to verify that slots are
   never too big ? Or do that in a storage module that depends on
   constants ? *)

let encoding = Data_encoding.uint16

let pp = Format.pp_print_int

let zero = 0

let to_int x = x

(* We assume 2^16 slots is big enough.

   We could increase that, but we would need to make sure there is no big
   performance penalty first. *)
let max_value = (1 lsl 16) - 1

let of_int_do_not_use_except_for_parameters i = i

let of_int i =
  if Compare.Int.(i < 0 || i > max_value) then error (Invalid_slot i) else ok i

let succ slot = of_int (slot + 1)

module Map = Map.Make (Compare.Int)
module Set = Set.Make (Compare.Int)

module Range = struct
  (* For now, we only need full intervals. If we ever need sparse ones, we
     could switch this representation to interval trees. [hi] and [lo] bounds
     are included. *)
  type t = Interval of {lo : int; hi : int}

  let create ~min ~count =
    error_when (min < 0) (Invalid_slot min) >>? fun () ->
    error_when (min > max_value) (Invalid_slot min) >>? fun () ->
    error_when (count < 1) (Invalid_slot count) >>? fun () ->
    error_when (count > max_value) (Invalid_slot count) >>? fun () ->
    let max = min + count - 1 in
    error_when (max > max_value) (Invalid_slot max) >>? fun () ->
    ok (Interval {lo = min; hi = max})

  let fold f init (Interval {lo; hi}) =
    let rec loop ~acc ~next =
      if Compare.Int.(next > hi) then acc
      else loop ~acc:(f acc next) ~next:(next + 1)
    in
    loop ~acc:(f init lo) ~next:(lo + 1)

  let fold_es f init (Interval {lo; hi}) =
    let rec loop ~acc ~next =
      if Compare.Int.(next > hi) then return acc
      else f acc next >>=? fun acc -> loop ~acc ~next:(next + 1)
    in
    f init lo >>=? fun acc -> loop ~acc ~next:(lo + 1)

  let rev_fold_es f init (Interval {lo; hi}) =
    let rec loop ~acc ~next =
      if Compare.Int.(next < lo) then return acc
      else f acc next >>=? fun acc -> loop ~acc ~next:(next - 1)
    in
    f init hi >>=? fun acc -> loop ~acc ~next:(hi - 1)
end

module Internal_for_tests = struct
  let of_int = of_int
end