%%% @doc
%%% ZX Daemon
%%%
%%% Resident execution daemon and runtime interface to Zomp.
%%% @end

-module(zx_daemon).
-export([]).


%%% App execution loop

-spec exec_wait(State) -> no_return()
    when State :: state().
%% @private
%% Execution maintenance loop.
%% Once an application is started by zompc this process will wait for a message from
%% the application if that application was written in a way to take advantage of zompc
%% facilities such as post-start upgrade checking.
%%
%% NOTE:
%% Adding clauses to this `receive' is where new functionality belongs.
%% It may make sense to add a `zompc_lib' as an available dependency authors could
%% use to interact with zompc without burying themselves under the complexity that
%% can come with naked send operations. (Would it make sense, for example, to have
%% the registered zompc process convert itself to a gen_server via zompc_lib to
%% provide more advanced functionality?)

exec_wait(State = #s{pid = none, mon = none}) ->
    receive
        {monitor, Pid} ->
            Mon = monitor(process, Pid),
            exec_wait(State#s{pid = Pid, mon = Mon});
        Unexpected ->
            ok = log(warning, "Unexpected message: ~tp", [Unexpected]),
            exec_wait(State)
    end;
exec_wait(State = #s{pid = Pid, mon = Mon}) ->
    receive
        {check_update, Requester, Ref} ->
            {Response, NewState} = check_update(State),
            Requester ! {Ref, Response},
            exec_wait(NewState);
        {exit, Reason} ->
            ok = log(info, "Exiting with: ~tp", [Reason]),
            halt(0);
        {'DOWN', Mon, process, Pid, normal} ->
            ok = log(info, "Application exited normally."),
            halt(0);
        {'DOWN', Mon, process, Pid, Reason} ->
            ok = log(warning, "Application exited with: ~tp", [Reason]),
            halt(1);
        Unexpected ->
            ok = log(warning, "Unexpected message: ~tp", [Unexpected]),
            exec_wait(State)
    end.


-spec check_update(State) -> {Response, NewState}
    when State    :: state(),
         Response :: term(),
         NewState :: state().
%% @private
%% Check for updated version availability of the current application.
%% The return value should probably provide up to three results, a Major, Minor and
%% Patch update, and allow the Requestor to determine what to do with it via some
%% interaction.

check_update(State) ->
    ok = log(info, "Would be checking for an update of the current application now..."),
    Response = "Nothing was checked, but you can imagine it to have been.",
    {Response, State}.