singleflight

-module(singleflight).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch, inline]).
-define(FILEPATH, "src/singleflight.gleam").
-export([config/2, fetch/3, start/2]).
-export_type([config/0, message/2, singleflight/2, state/2]).

-type config() :: {config, integer(), integer()}.

-type message(FLZ, FMA) :: {request,
        FLZ,
        fun((FLZ) -> FMA),
        gleam@erlang@process:subject(FMA)} |
    {done, FLZ, FMA}.

-opaque singleflight(FMB, FMC) :: {singleflight,
        gleam@erlang@process:subject(message(FMB, FMC)),
        integer()}.

-type state(FMD, FME) :: {state,
        gleam@dict:dict(FMD, list(gleam@erlang@process:subject(FME))),
        gleam@erlang@process:subject(message(FMD, FME))}.

-file("src/singleflight.gleam", 26).
-spec config(integer(), integer()) -> config().
config(Initialisation_timeout_ms, Fetch_timeout_ms) ->
    {config, Initialisation_timeout_ms, Fetch_timeout_ms}.

-file("src/singleflight.gleam", 52).
-spec fetch(singleflight(FMN, FMO), FMN, fun((FMN) -> FMO)) -> FMO.
fetch(Singleflight, Key, Work) ->
    {singleflight, Subject, Fetch_timeout_ms} = Singleflight,
    gleam@otp@actor:call(
        Subject,
        Fetch_timeout_ms,
        fun(Caller) -> {request, Key, Work, Caller} end
    ).

-file("src/singleflight.gleam", 60).
-spec handle_message(state(FMR, FMS), message(FMR, FMS)) -> gleam@otp@actor:next(state(FMR, FMS), message(FMR, FMS)).
handle_message(State, Message) ->
    case Message of
        {request, Key, Work, Caller} ->
            case gleam_stdlib:map_get(erlang:element(2, State), Key) of
                {ok, Waiters} ->
                    gleam@otp@actor:continue(
                        {state,
                            gleam@dict:insert(
                                erlang:element(2, State),
                                Key,
                                [Caller | Waiters]
                            ),
                            erlang:element(3, State)}
                    );

                {error, nil} ->
                    Self = erlang:element(3, State),
                    proc_lib:spawn_link(
                        fun() ->
                            Result = Work(Key),
                            gleam@otp@actor:send(Self, {done, Key, Result})
                        end
                    ),
                    gleam@otp@actor:continue(
                        {state,
                            gleam@dict:insert(
                                erlang:element(2, State),
                                Key,
                                [Caller]
                            ),
                            erlang:element(3, State)}
                    )
            end;

        {done, Key@1, Result@1} ->
            case gleam_stdlib:map_get(erlang:element(2, State), Key@1) of
                {ok, Waiters@1} ->
                    gleam@list:each(
                        Waiters@1,
                        fun(Waiter) ->
                            gleam@erlang@process:send(Waiter, Result@1)
                        end
                    );

                {error, nil} ->
                    nil
            end,
            gleam@otp@actor:continue(
                {state,
                    gleam@dict:delete(erlang:element(2, State), Key@1),
                    erlang:element(3, State)}
            )
    end.

-file("src/singleflight.gleam", 33).
-spec start(config(), gleam@erlang@process:name(message(FMF, FMG))) -> {ok,
        gleam@otp@actor:started(singleflight(FMF, FMG))} |
    {error, gleam@otp@actor:start_error()}.
start(Config, Name) ->
    {config, Initialisation_timeout_ms, Fetch_timeout_ms} = Config,
    _pipe@2 = gleam@otp@actor:new_with_initialiser(
        Initialisation_timeout_ms,
        fun(Self) ->
            _pipe = gleam@otp@actor:initialised({state, maps:new(), Self}),
            _pipe@1 = gleam@otp@actor:returning(
                _pipe,
                {singleflight, Self, Fetch_timeout_ms}
            ),
            {ok, _pipe@1}
        end
    ),
    _pipe@3 = gleam@otp@actor:on_message(_pipe@2, fun handle_message/2),
    _pipe@4 = gleam@otp@actor:named(_pipe@3, Name),
    gleam@otp@actor:start(_pipe@4).