open Lwt.Syntax
open Lwt.Infix
open Lwt_react
open Stream

type step =
  | Starting_stream
  | Negotiating_feature of Feature.requirement * features
  | Logged_in of features

type state =
  | Disconnected
  | Connecting of Portal.domain
  (* TCP/WebSocket connected, not connected in XMPP-land *)
  | Connected of Portal.t * step

type t = {
    state : state signal;
    update : state -> unit;
  }

(** [create domain config] is a promise containing a signal representing the portal
    connected to the XMPP server located at [domain], and all its supported features.

    When calling the function, the portal will try to connect to the provided domain.

    Basically, it conforms to {{:
    https://datatracker.ietf.org/doc/html/rfc6120#section-4.3 }}, and gets the Portal in
    a "ready" state. *)
let create (domain : Portal.domain) (config : config) : t Lwt.t =
  let needs_restart = function
    | Feature.Mechanisms _ | STARTTLS -> true
    | _ -> false
  and features_next_state = function
    | feature :: rest -> Negotiating_feature (feature, rest)
    (* No features returned by stream start. Connection is completed. *)
    | [] -> Logged_in []
  and eq s1 s2 =  (* TODO: move this closer to the state type *)
    match s1, s2 with
    | Connected (_, step1), Connected (_, step2) -> step1 = step2
    | _ -> s1 = s2
  in
  let state, update = S.create ~eq Disconnected in
  let+ () = S.map_s
              (function
               | Connecting domain ->
                  let+ portal = Portal.connect domain
                  in update (Connected (portal, Starting_stream))
               | Connected (portal, Starting_stream) ->
                  let+ features = Stream.start domain portal
                  in let next_state = features_next_state features
                     in update (Connected (portal, next_state))
               | Connected (portal, Negotiating_feature (feature, features)) ->
                  let+ () = negotiate feature portal config
                  in let next_state = if needs_restart (Feature.unwrap feature)
                                      then Starting_stream
                                      else features_next_state features
                     in update (Connected (portal, next_state))
               | _ -> Lwt.return_unit)
              state >|= S.keep;
  in { state; update }