%%%-------------------------------------------------------------------
%%% @author anlicheng
%%% @copyright (C) 2025, <COMPANY>
%%% @doc
%%%
%%% @end
%%% Created : 26. 9月 2025 12:19
%%%-------------------------------------------------------------------
-module(iot_event_stream_observer).
-author("anlicheng").

-behaviour(gen_server).

%% API
-export([start_link/0]).
-export([add_listener/2, stream_data/3, stream_close/1]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

-define(SERVER, ?MODULE).

-record(state, {
    listeners = #{}
}).

%%%===================================================================
%%% API
%%%===================================================================

-spec add_listener(ListenerPid :: pid(), TaskId :: integer()) -> ok.
add_listener(ListenerPid, TaskId) when is_pid(ListenerPid), is_integer(TaskId) ->
    gen_server:call(?SERVER, {add_listener, ListenerPid, TaskId}).

-spec stream_data(TaskId :: integer(), Type :: binary(), Stream :: binary()) -> no_return().
stream_data(TaskId, Type, Stream) when is_integer(TaskId), is_binary(Type), is_binary(Stream) ->
    gen_server:cast(?SERVER, {stream_data, TaskId, Type, Stream}).

-spec stream_close(TaskId :: integer()) -> no_return().
stream_close(TaskId) when is_integer(TaskId) ->
    gen_server:cast(?SERVER, {stream_close, TaskId}).

%% @doc Spawns the server and registers the local name (unique)
-spec(start_link() ->
    {ok, Pid :: pid()} | ignore | {error, Reason :: term()}).
start_link() ->
    gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================

%% @private
%% @doc Initializes the server
-spec(init(Args :: term()) ->
    {ok, State :: #state{}} | {ok, State :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term()} | ignore).
init([]) ->
    {ok, #state{}}.

%% @private
%% @doc Handling call messages
-spec(handle_call(Request :: term(), From :: {pid(), Tag :: term()},
    State :: #state{}) ->
    {reply, Reply :: term(), NewState :: #state{}} |
    {reply, Reply :: term(), NewState :: #state{}, timeout() | hibernate} |
    {noreply, NewState :: #state{}} |
    {noreply, NewState :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term(), Reply :: term(), NewState :: #state{}} |
    {stop, Reason :: term(), NewState :: #state{}}).
handle_call({add_listener, ListenerPid, TaskId}, _From, State = #state{listeners = Listeners}) ->
    erlang:monitor(process, ListenerPid),
    {reply, ok, State#state{listeners = maps:put(TaskId, ListenerPid, Listeners)}}.

%% @private
%% @doc Handling cast messages
-spec(handle_cast(Request :: term(), State :: #state{}) ->
    {noreply, NewState :: #state{}} |
    {noreply, NewState :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term(), NewState :: #state{}}).
handle_cast({stream_data, TaskId, Type, Stream}, State = #state{listeners = Listeners}) ->
    case maps:find(TaskId, Listeners) of
        error ->
            ok;
        {ok, ListenerPid} ->
            is_process_alive(ListenerPid) andalso ListenerPid ! {stream_data, TaskId, Type, Stream}
    end,
    {noreply, State};
handle_cast({stream_close, TaskId}, State = #state{listeners = Listeners}) ->
    case maps:find(TaskId, Listeners) of
        error ->
            ok;
        {ok, ListenerPid} ->
            is_process_alive(ListenerPid) andalso ListenerPid ! {stream_close, TaskId}
    end,
    {noreply, State}.

%% @private
%% @doc Handling all non call/cast messages
-spec(handle_info(Info :: timeout() | term(), State :: #state{}) ->
    {noreply, NewState :: #state{}} |
    {noreply, NewState :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term(), NewState :: #state{}}).
handle_info({'DOWN', _Ref, process, Pid, _Reason}, State = #state{listeners = Listeners}) ->
    NListeners = maps:filter(fun(_, ListenerPid) -> ListenerPid /= Pid end, Listeners),
    {noreply, State#state{listeners = NListeners}}.

%% @private
%% @doc This function is called by a gen_server when it is about to
%% terminate. It should be the opposite of Module:init/1 and do any
%% necessary cleaning up. When it returns, the gen_server terminates
%% with Reason. The return value is ignored.
-spec(terminate(Reason :: (normal | shutdown | {shutdown, term()} | term()),
    State :: #state{}) -> term()).
terminate(_Reason, _State = #state{}) ->
    ok.

%% @private
%% @doc Convert process state when code is changed
-spec(code_change(OldVsn :: term() | {down, term()}, State :: #state{},
    Extra :: term()) ->
    {ok, NewState :: #state{}} | {error, Reason :: term()}).
code_change(_OldVsn, State = #state{}, _Extra) ->
    {ok, State}.

%%%===================================================================
%%% Internal functions
%%%===================================================================