nova

%%% @author Niclas Axelsson <niclas@burbas.se>
%%% @doc
%%% Callback controller for handling websockets
%%% @end

-module(nova_ws_handler).

-export([
         init/2,
         terminate/3,
         websocket_init/1,
         websocket_handle/2,
         websocket_info/2
        ]).

-include_lib("kernel/include/logger.hrl").

-type nova_ws_state() :: #{controller_data := map(),
                           mod := atom(),
                           _ := _}.

-export_type([nova_ws_state/0]).

%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Public functions      %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%
init(Req = #{method := _Method, plugins := Plugins}, State = #{module := Module}) ->
    %% Call the http-handler in order to correctly handle potential plugins for the http-request
    ControllerData = maps:get(controller_data, State, #{}),
    State0 = State#{mod => Module,
                    plugins => Plugins},
    ControllerData2 = ControllerData#{req => Req},
    upgrade_ws(Module, Req, State0, ControllerData2).


upgrade_ws(Module, Req, State, ControllerData) ->
    case Module:init(ControllerData) of
        {ok, NewControllerData} ->
            {cowboy_websocket, Req, State#{controller_data => NewControllerData}};
        Error ->
            ?LOG_ERROR(#{msg => <<"Websocket handler returned unknown result">>, handler => Module, returned => Error}),
            nova_router:render_status_page(500, Req)
    end.

websocket_init(State = #{mod := Mod}) ->
    %% Inject the websocket process into the state
    ControllerData = maps:get(controller_data, State, #{}),
    NewState = State#{controller_data => ControllerData#{ws_handler_process => self()}},

    case erlang:function_exported(Mod, websocket_init, 1) of
        true ->
            handle_ws(Mod, websocket_init, [], NewState);
        _ ->
            {ok, NewState}
    end.

websocket_handle(Frame, State = #{mod := Mod}) ->
    handle_ws(Mod, websocket_handle, [Frame], State).

websocket_info(Msg, State = #{mod := Mod}) ->
    handle_ws(Mod, websocket_info, [Msg], State).

terminate(Reason, PartialReq, State = #{controller_data := ControllerData, mod := Mod, plugins := Plugins}) ->
    case erlang:function_exported(Mod, terminate, 3) of
        true ->
            erlang:apply(Mod, terminate, [Reason, PartialReq, ControllerData]),
            %% Call post_ws_connection-plugins
            TerminatePlugins = proplists:get_value(post_ws_connection, Plugins, []),
            ControllerState = #{module => Mod,
                                function => terminate,
                                arguments => [Reason, PartialReq, State]},
            run_plugins(TerminatePlugins, post_ws_connection, ControllerState, State);
        _ ->
            ok
    end;
terminate(Reason, PartialReq, State) ->
    ?LOG_ERROR(#{msg => <<"Terminate called">>, reason => Reason, partial_req => PartialReq, state => State}),
    ok.


handle_ws(Mod, Func, Args, State = #{controller_data := _ControllerData, plugins := Plugins}) ->
    PrePlugins = proplists:get_value(pre_ws_request, Plugins, []),
    ControllerState = #{module => Mod,
                        function => Func,
                        arguments => Args},
    %% First run the pre-plugins and if everything goes alright we continue
    State0 = State#{commands => []},
    case run_plugins(PrePlugins, pre_ws_request, ControllerState, State0) of
        {ok, State1} ->
            case invoke_controller(Mod, Func, Args, State1) of
                {stop, _StopReason} = S ->
                    S;
                State2 ->
                    %% Run the post-plugins
                    PostPlugins = proplists:get_value(post_ws_request, Plugins, []),
                    {ok, State3 = #{commands := Cmds}} = run_plugins(PostPlugins, post_ws_request,
                                                                     ControllerState, State2),
                    %% Remove the commands from the map
                    State4 = maps:remove(commands, State3),

                    %% Check if we are hibernating
                    case maps:get(hibernate, State4, false) of
                        false ->
                            {Cmds, State4};
                        _ ->
                            {Cmds, maps:remove(hibernate, State4), hibernate}
                    end
            end;
        {stop, _} = Stop ->
            ?LOG_WARNING(#{msg => <<"Got stop signal">>, signal => Stop}),
            Stop
    end;
handle_ws(Mod, Func, Args, State) ->
    handle_ws(Mod, Func, Args, State#{controller_data => #{}}).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Private functions      %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%


invoke_controller(Mod, Func, Args, State = #{controller_data := ControllerData}) ->
    try erlang:apply(Mod, Func, Args ++ [ControllerData]) of
        RetObj ->
            case nova_handlers:get_handler(ws) of
                {ok, Callback} ->
                    Callback(RetObj, State);
                {error, not_found} ->
                    ?LOG_ERROR(#{msg => <<"Websocket handler not found. Check that a handler is
                                           registered on handle 'ws'">>,
                                   controller => Mod, function => Func, return => RetObj}),
                    {stop, State}
            end
    catch
        Class:Reason:Stacktrace ->
            ?LOG_ERROR(#{msg => <<"Controller crashed">>, class => Class,
                           reason => Reason, stacktrace => Stacktrace}),
            {stop, State}
    end.


run_plugins([], _Callback, #{controller_result := {stop, _} = Signal}, _State) ->
    Signal;
run_plugins([], _Callback, _ControllerState, State) ->
    {ok, State};
run_plugins([{Module, Options}|Tl], Callback, ControllerState, State) ->
    try erlang:apply(Module, Callback, [ControllerState, State, Options]) of
        {ok, ControllerState0, State0} ->
            run_plugins(Tl, Callback, ControllerState0, State0);
        %% Stop indicates that we want the entire pipe of plugins/controller to be stopped.
        {stop, State0} ->
            {stop, State0};
        %% Break is used to signal that we are stopping further executing of plugins within the same Callback
        {break, State0} ->
            {ok, State0};
        {error, Reason} ->
            ?LOG_ERROR(#{msg => <<"Plugin returned error">>, plugin => Module, function => Callback, reason => Reason}),
            {stop, State}
    catch
        Class:Reason:Stacktrace ->
            ?LOG_ERROR(#{msg => <<"Plugin crashed">>, class => Class, reason => Reason, stacktrace => Stacktrace}),
            {stop, State}
    end.



-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").

-endif.