%% plans/ra_kernel.erl — RA/TA persistent-kernel SPIKE.
%% A minimal long-lived next/ kernel: starts flow_store + registers the publish-digest flow, then
%% blocks in http:listen — keeping the er-scheduler (and flow_store's gen_server) alive across
%% requests. Two routes drive flow_store over HTTP: GET /start (start a newsletter flow → suspend)
%% and GET /resume (resume instance 1 → done). If /resume completes in a SEPARATE request from
%% /start, the gen_server persisted across requests — the persistent-kernel prerequisite for
%% RA-live + TA-live holds.
-module(ra_kernel).
-export([start/1]).

start(Port) ->
    flow_store:start_link(),
    FF = fun (_) -> [f1, f2, f3] end,
    flow_store:register_flow(bd, blog_publish_digest:build([{fetch_followers, FF}])),
    http:listen(Port, fun (Req) -> route(Req) end).

route(Req) ->
    [{status, 200}, {headers, []}, {body, respond(field(path, Req))}].

%% /start  (bytes 47,115,116,97,114,116)
respond(<<47,115,116,97,114,116>>) ->
    Env = [{activity, [{type, create}, {actor, alice}, {id, <<110,49>>},
                       {object, [{type, article}, {category, newsletter}]}]},
           {actor, alice}],
    case flow_store:start(bd, Env) of
        {ok, _Id, {flow_suspended, _}} -> <<"start:suspended">>;
        {ok, _Id, {flow_done, _}}      -> <<"start:done">>;
        _                              -> <<"start:other">>
    end;
%% /resume  (bytes 47,114,101,115,117,109,101)
respond(<<47,114,101,115,117,109,101>>) ->
    case flow_store:resume(1, morning_ts) of
        {ok, {flow_done, _}} -> <<"resume:done">>;
        {flow_done, _}       -> <<"resume:done">>;
        _                    -> <<"resume:other">>
    end;
respond(_) -> <<"path:unknown">>.

field(K, [{K, V} | _]) -> V;
field(K, [_ | Rest]) -> field(K, Rest);
field(_, []) -> nil.