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(* Open Source License                                                       *)
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open Misc

type error +=
  | Unknown of {
      oldest : Cycle_repr.t;
      cycle : Cycle_repr.t;
      latest : Cycle_repr.t;
    }

(* `Permanent *)

let () =
  register_error_kind
    `Permanent
    ~id:"seed.unknown_seed"
    ~title:"Unknown seed"
    ~description:"The requested seed is not available"
    ~pp:(fun ppf (oldest, cycle, latest) ->
      if Cycle_repr.(cycle < oldest) then
        Format.fprintf
          ppf
          "The seed for cycle %a has been cleared from the context  (oldest \
           known seed is for cycle %a)"
          Cycle_repr.pp
          cycle
          Cycle_repr.pp
          oldest
      else
        Format.fprintf
          ppf
          "The seed for cycle %a has not been computed yet  (latest known \
           seed is for cycle %a)"
          Cycle_repr.pp
          cycle
          Cycle_repr.pp
          latest)
    Data_encoding.(
      obj3
        (req "oldest" Cycle_repr.encoding)
        (req "requested" Cycle_repr.encoding)
        (req "latest" Cycle_repr.encoding))
    (function
      | Unknown {oldest; cycle; latest} ->
          Some (oldest, cycle, latest)
      | _ ->
          None)
    (fun (oldest, cycle, latest) -> Unknown {oldest; cycle; latest})

let compute_for_cycle c ~revealed cycle =
  match Cycle_repr.pred cycle with
  | None ->
      assert false (* should not happen *)
  | Some previous_cycle ->
      let levels = Level_storage.levels_with_commitments_in_cycle c revealed in
      let combine (c, random_seed, unrevealed) level =
        Storage.Seed.Nonce.get c level
        >>=? function
        | Revealed nonce ->
            Storage.Seed.Nonce.remove_existing c level
            >|=? fun c -> (c, Seed_repr.nonce random_seed nonce, unrevealed)
        | Unrevealed u ->
            Storage.Seed.Nonce.remove_existing c level
            >|=? fun c -> (c, random_seed, u :: unrevealed)
      in
      Storage.Seed.For_cycle.get c previous_cycle
      >>=? fun prev_seed ->
      let seed = Seed_repr.deterministic_seed prev_seed in
      fold_left_s combine (c, seed, []) levels
      >>=? fun (c, seed, unrevealed) ->
      Storage.Seed.For_cycle.init c cycle seed >|=? fun c -> (c, unrevealed)

let for_cycle ctxt cycle =
  let preserved = Constants_storage.preserved_cycles ctxt in
  let current_level = Level_storage.current ctxt in
  let current_cycle = current_level.cycle in
  let latest =
    if Cycle_repr.(current_cycle = root) then
      Cycle_repr.add current_cycle (preserved + 1)
    else Cycle_repr.add current_cycle preserved
  in
  let oldest =
    match Cycle_repr.sub current_cycle preserved with
    | None ->
        Cycle_repr.root
    | Some oldest ->
        oldest
  in
  error_unless
    Cycle_repr.(oldest <= cycle && cycle <= latest)
    (Unknown {oldest; cycle; latest})
  >>?= fun () -> Storage.Seed.For_cycle.get ctxt cycle

let clear_cycle c cycle = Storage.Seed.For_cycle.remove_existing c cycle

let init ctxt =
  let preserved = Constants_storage.preserved_cycles ctxt in
  List.fold_left2
    (fun ctxt c seed ->
      ctxt
      >>=? fun ctxt ->
      let cycle = Cycle_repr.of_int32_exn (Int32.of_int c) in
      Storage.Seed.For_cycle.init ctxt cycle seed)
    (return ctxt)
    (0 --> (preserved + 1))
    (Seed_repr.initial_seeds (preserved + 2))

let cycle_end ctxt last_cycle =
  let preserved = Constants_storage.preserved_cycles ctxt in
  ( match Cycle_repr.sub last_cycle preserved with
  | None ->
      return ctxt
  | Some cleared_cycle ->
      clear_cycle ctxt cleared_cycle )
  >>=? fun ctxt ->
  match Cycle_repr.pred last_cycle with
  | None ->
      return (ctxt, [])
  | Some revealed ->
      (* cycle with revelations *)
      let inited_seed_cycle = Cycle_repr.add last_cycle (preserved + 1) in
      compute_for_cycle ctxt ~revealed inited_seed_cycle