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(* Open Source License                                                       *)
(* Copyright (c) 2018 Dynamic Ledger Solutions, Inc. <contact@tezos.com>     *)
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open Lwt.Syntax

module Inttbl = Hashtbl.Make (struct
  type t = int

  let equal (x : int) (y : int) = x = y

  let hash = Hashtbl.hash
end)

type t = {
  id : int;
  alpha : int;
  mutable total : int64;
  mutable current : int;
  mutable average : int;
}

type state = {
  refresh_interval : float;
  counters : t Inttbl.t;
  updated : unit Lwt_condition.t;
  mutable update_hook : (unit -> unit) list;
}

let worker_loop state () =
  let rec inner sleep time_at_entry =
    let* () = sleep in
    let sleep = Lwt_unix.sleep state.refresh_interval in
    let now = Mtime_clock.elapsed () in
    let elapsed = int_of_float Mtime.Span.(to_ms now -. to_ms time_at_entry) in
    Inttbl.iter
      (fun _ c ->
        c.average <-
          (c.alpha * c.current / elapsed) + ((1000 - c.alpha) * c.average / 1000) ;
        c.current <- 0)
      state.counters ;
    List.iter (fun f -> f ()) state.update_hook ;
    Lwt_condition.broadcast state.updated () ;
    inner sleep now
  in
  inner (Lwt_unix.sleep state.refresh_interval) (Mtime_clock.elapsed ())

let fresh_state ~id ~refresh_interval =
  if refresh_interval <= 0.0 then
    raise (Invalid_argument "Moving_average.fresh_state") ;
  let state =
    {
      refresh_interval;
      counters = Inttbl.create 41;
      updated = Lwt_condition.create ();
      update_hook = [];
    }
  in
  Lwt.ignore_result
    (Lwt_utils.worker
       (Format.asprintf "counter(%s)" id)
       ~on_event:Internal_event.Lwt_worker_event.on_event
       ~run:(worker_loop state)
       ~cancel:(fun _ -> Lwt.return_unit)) ;
  state

let on_update state f = state.update_hook <- f :: state.update_hook

let create =
  let cpt = ref 0 in
  fun state ~init ~alpha ->
    if not (0. < alpha && alpha <= 1.) then
      raise (Invalid_argument "Moving_average.create") ;
    let id = !cpt in
    incr cpt ;
    let alpha = int_of_float (1000. *. alpha) in
    let c = {id; alpha; total = 0L; current = 0; average = init} in
    Inttbl.add state.counters id c ;
    c

let add c x =
  c.total <- Int64.(add c.total (of_int x)) ;
  c.current <- c.current + x

let destroy state c = Inttbl.remove state.counters c.id

let updated {updated; _} = updated

type stat = {total : int64; average : int}

let stat ({total; average; _} : t) : stat = {total; average}