booklet

-module(booklet_ffi).
-compiler([no_auto_import, nowarn_conflicting_behaviours, nowarn_nomatch]).

-behaviour(application).
-export([start/2, stop/1]).

-behaviour(gen_server).
% The nowarn rule doesn't work so I figured I can just disable that line
% -behaviour(supervisor).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

-export([make/1, get/1, update/2]).


% -- Public API ----------------------------------------------------------------


make(DefaultValue) ->
    Table = gen_server:call(booklet, get),
    Key = make_ref(),
    true = ets:insert_new(Table, {Key, 0, DefaultValue}),
    {Table, Key}.


get({Table, Key}) ->
    ets:lookup_element(Table, Key, 3).


update({Table, Key}, Updater) ->
    [{Key, Rev, Value}] = ets:lookup(Table, Key),
    NewValue = Updater(Value),
    Pattern = {Key, Rev, '_'},
    Replacement = {const, {Key, Rev + 1, NewValue}},
    case ets:select_replace(Table, [{Pattern, [], [Replacement]}]) of
        0 -> update({Table, Key}, Updater);
        _ -> NewValue
    end.


% -- APPLICATION ---------------------------------------------------------------

start(_StartType, _StartArgs) ->
    supervisor:start_link(?MODULE, supervisor).

stop(_State) ->
    ok.

% -- SUPERVISOR ----------------------------------------------------------------

init(supervisor) ->
    SupFlags = #{
        strategy => one_for_one,
        intensity => 6,
        period => 3600
    },
    ChildSpec = #{
        id => booklet,
        start => {gen_server, start_link, [{local, booklet}, ?MODULE, gen_server, []]},
        shutdown => brutal_kill,
        modules => [?MODULE]
    },
    {ok, {SupFlags, [ChildSpec]}};

% -- ACTOR ---------------------------------------------------------------------

init(gen_server) ->
    Table = ets:new(booklet, [set, public, {keypos, 1}, {write_concurrency, auto}, {read_concurrency, true}]),
    {ok, Table}.

handle_call(get, _From, Table) ->
    {reply, Table, Table}.

handle_cast(_Msg, Table) ->
    {noreply, Table}.

handle_info(_Info, Table) ->
    {noreply, Table}.

terminate(_Reason, _Table) ->
    ok.

code_change(_Prev, Table, _Extra) ->
    {ok, Table}.