-module(stomp_worker).
-behaviour(gen_server).
%% API.
-export([start_link/0]).
%% gen_server.
-export([init/1]).
-export([handle_call/3]).
-export([handle_cast/2]).
-export([handle_info/2]).
-export([terminate/2]).
-export([code_change/3]).
-include("stomp.hrl").
%% State of a stomp_worker
-record(state, {connection :: port(),
next_sub :: sub_id(),
subscriptions :: #{ destination() => sub_id() },
subscribers :: #{ destination() => pid() }
}).
-type state() :: #state{}.
%% API implementation
-spec start_link() -> {ok, pid()}.
start_link() ->
{ok, Pid} = gen_server:start_link(?MODULE, [], []),
register(?MODULE, Pid),
{ok, Pid}.
%% gen_server implementation
-spec init(any()) -> {ok, state()}.
init(_Args) ->
%% Fetch configuration from app config
{ok, Host} = application:get_env(stomp, host),
Port = application:get_env(stomp, port, 61613),
Login = application:get_env(stomp, login),
Pass = application:get_env(stomp, passcode),
%% Catch exit signals from linked processes (subscribers dying)
process_flag(trap_exit, true),
%% Establish connection
{ok, Conn} = connect(Host, Port, Login, Pass),
{ok, #state{connection = Conn,
next_sub = 0,
subscriptions = #{},
subscribers = #{}}}.
%% Handle subscription calls
handle_call({subscribe, Dest, Ack}, From, State) ->
%% Subscribe to new destination
SubId = State#state.next_sub,
ok = subscribe(State#state.connection, SubId, Dest, Ack),
%% Add subscription and subscriber to state
Subscriptions = maps:put(SubId, Dest, State#state.subscriptions),
Subscribers = maps:put(SubId, From, State#state.subscribers),
NextSub = SubId + 1,
NewState = State#state{subscriptions = Subscriptions,
subscribers = Subscribers,
next_sub = NextSub },
{reply, {ok, SubId}, NewState};
handle_call(_Req, _From, State) ->
{reply, ignored, State}.
%% Unused gen_server callbacks
handle_info(_Msg, State) ->
{noreply, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%% Private functions
-spec connect(list(), integer(), any(), any()) -> {ok, port()}.
connect(Host, Port, Login, Pass) ->
%% STOMP CONNECT frame
Connect = connect_frame(Host, Login, Pass),
%% TODO: Configurable buffer size
%% Frames larger than the user-level buffer will be truncated, so it should
%% never be smaller than the largest expected messages.
{ok, Socket} = gen_tcp:connect(Host, Port, [binary,
{packet, line},
{line_delimiter, $\0},
{buffer, 262144}]),
ok = gen_tcp:send(Socket, Connect),
{ok, Socket}.
-spec subscribe(port(), sub_id(), destination(), ack_mode()) -> ok.
subscribe(Socket, Id, Queue, Ack) ->
{ok, SubscribeFrame} = subscribe_frame(Id, Queue, Ack),
gen_tcp:send(Socket, SubscribeFrame).
%%% Making STOMP protocol frames
%% Format a header
-spec format_header({binary(), binary()}) -> binary().
format_header({Key, Val}) ->
<<Key, ":", Val, "\n">>.
%% Build a single STOMP frame
-spec make_frame(binary(),
list({binary(), binary()}),
binary())
-> {ok, iolist()}.
make_frame(Command, HeaderMap, Body) ->
Headers = lists:map(fun format_header/1, HeaderMap),
Frame = [Command, <<"\n">>, Headers, <<"\n">>, Body, <<0>>],
{ok, Frame}.
%%% Default frames
-spec connect_frame(list(), any(), any()) -> iolist().
connect_frame(Host, {ok, Login}, {ok, Pass}) ->
make_frame(<<"CONNECT">>,
[{"accept-version", "1.2"},
{"host", Host},
{"login", Login},
{"passcode", Pass},
{"heart-beat", "0,5000"}],
[]);
connect_frame(Host, _Login, _Pass) ->
make_frame(<<"CONNECT">>,
[{"accept-version", "1.2"},
{"host", Host},
%% Expect a server heartbeat every 5 seconds, let the server
%% expect one every 10. We don't actually check this and just
%% echo server heartbeats.
%% TODO: For now the server is told not to expect replies due to
%% a weird behaviour.
{"heart-beat", "0,5000"}],
[]).
-spec subscribe_frame(sub_id(), destination(), ack_mode()) -> iolist().
subscribe_frame(Id, Queue, Ack) ->
make_frame(<<"SUBSCRIBE">>,
[{"id", integer_to_binary(Id)},
{"destination", Queue},
{"ack", ack_mode_to_binary(Ack)}],
[]).
-spec ack_mode_to_binary(ack_mode()) -> binary().
ack_mode_to_binary(AckMode) ->
case AckMode of
auto -> <<"auto">>;
client -> <<"client">>;
client_individual -> <<"client-individual">>
end.
%% -spec ack_frame(binary()) -> iolist().
%% ack_frame(MessageID) ->
%% make_frame(<<"ACK">>,
%% [{"id", MessageID}],
%% []).
