%%%-------------------------------------------------------------------
%%% @doc Пилотные метрики ИИ-подсказок (PRODUCT-AI, Spec#22).
%%%
%%% Front присылает счётчики shown/confirm/dismiss по паттерну подсказки;
%%% Back агрегирует их по дням (таблица ai_hint_metric) и отдаёт админам
%%% сводку для решения о старте L2 (гейты канона: hint CTR и доля
%%% активных с >=2 подтверждёнными ghost-записями за месяц).
%%%
%%% Данные привязаны к opt-in: клиент шлёт метрики только при включённых
%%% подсказках (preferences.ai_hints).
%%% @end
%%%-------------------------------------------------------------------
-module(logic_ai_metrics).

-export([record_events/2, summary/0]).

-include("records.hrl").

-define(TABLE, ai_hint_metric).
-define(MAX_BATCH, 20).
-define(MAX_PATTERN, 96).
-define(RETENTION_DAYS, 92).
-define(PRUNE_ROWS_PER_USER, 500).
-define(RL_TABLE, eventhub_ai_metrics_rl).
-define(RL_LIMIT, 30).      % запросов на пользователя
-define(RL_WINDOW_MS, 60000).

%%%===================================================================
%%% Запись событий
%%%===================================================================

-spec record_events(binary(), [map()]) ->
  {ok, non_neg_integer()} | {error, invalid_body | rate_limited}.
record_events(UserId, Events) when is_binary(UserId), is_list(Events),
    Events =/= [], length(Events) =< ?MAX_BATCH ->
  case allow(UserId) of
    false ->
      {error, rate_limited};
    true ->
      Day = today(),
      case normalize_events(Events, []) of
        {ok, Norm} ->
          {atomic, Count} = mnesia:transaction(fun() ->
            lists:foreach(fun({Kind, Pattern}) ->
              increment(UserId, Day, Pattern, Kind)
            end, Norm),
            maybe_prune(UserId, Day),
            length(Norm)
          end),
          {ok, Count};
        error ->
          {error, invalid_body}
      end
  end;
record_events(_UserId, _Events) ->
  {error, invalid_body}.

increment(UserId, Day, Pattern, Kind) ->
  Key = {UserId, Day, Pattern, Kind},
  Row = case mnesia:read(?TABLE, Key, write) of
    [Existing] -> Existing;
    [] -> #ai_hint_metric{id = Key, user_id = UserId, day = Day,
                          pattern_key = Pattern, kind = Kind, count = 0}
  end,
  mnesia:write(Row#ai_hint_metric{
    count = Row#ai_hint_metric.count + 1,
    updated_at = calendar:universal_time()
  }).

%% Ленивая чистка: если у пользователя накопилось много строк,
%% удаляем всё старше RETENTION_DAYS.
maybe_prune(UserId, Day) ->
  Rows = mnesia:index_read(?TABLE, UserId, user_id),
  case length(Rows) > ?PRUNE_ROWS_PER_USER of
    true ->
      Cutoff = shift_day(Day, -?RETENTION_DAYS),
      lists:foreach(fun(#ai_hint_metric{day = D} = R) when D < Cutoff ->
        mnesia:delete_object(R);
        (_) -> ok
      end, Rows);
    false -> ok
  end.

normalize_events([], Acc) ->
  {ok, lists:reverse(Acc)};
normalize_events([E | Rest], Acc) when is_map(E) ->
  Kind = maps:get(<<"kind">>, E, undefined),
  Pattern = maps:get(<<"pattern">>, E, <<>>),
  case valid_kind(Kind) andalso valid_pattern(Pattern) of
    true -> normalize_events(Rest, [{Kind, Pattern} | Acc]);
    false -> error
  end;
normalize_events(_, _) ->
  error.

valid_kind(<<"shown">>) -> true;
valid_kind(<<"confirm">>) -> true;
valid_kind(<<"dismiss">>) -> true;
valid_kind(_) -> false.

valid_pattern(P) when is_binary(P), byte_size(P) > 0, byte_size(P) =< ?MAX_PATTERN -> true;
valid_pattern(_) -> false.

%%%===================================================================
%%% Сводка для админов
%%%===================================================================

-spec summary() -> map().
summary() ->
  Today = today(),
  MonthAgo = shift_day(Today, -30),
  Init = #{
    by_kind => #{},
    active_30d => sets:new(),
    confirms_by_user_30d => #{},
    confirms_by_pattern => #{}
  },
  {atomic, Acc} = mnesia:transaction(fun() ->
    mnesia:foldl(fun(R, A) -> fold_row(R, MonthAgo, A) end, Init, ?TABLE)
  end),
  ByKind = maps:get(by_kind, Acc),
  Active = sets:size(maps:get(active_30d, Acc)),
  ConfirmsByUser = maps:get(confirms_by_user_30d, Acc),
  UsersGe2 = maps:size(maps:filter(fun(_, N) -> N >= 2 end, ConfirmsByUser)),
  TopPatterns = lists:sublist(
    lists:reverse(lists:sort(maps:to_list(maps:get(confirms_by_pattern, Acc)))), 10),
  #{
    <<"by_kind">> => ByKind,
    <<"active_users_30d">> => Active,
    <<"users_with_confirms_ge2_30d">> => UsersGe2,
    <<"gate_ratio_30d">> => ratio(UsersGe2, Active),
    <<"top_patterns_by_confirm">> =>
      [#{<<"pattern">> => P, <<"confirms">> => N} || {P, N} <- TopPatterns],
    <<"retention_days">> => ?RETENTION_DAYS
  }.

fold_row(#ai_hint_metric{user_id = U, day = D, pattern_key = P, kind = K, count = N},
    MonthAgo, Acc) ->
  ByKind = maps:get(by_kind, Acc),
  Acc1 = Acc#{by_kind => maps:update_with(K, fun(V) -> V + N end, N, ByKind)},
  case D >= MonthAgo of
    false -> Acc1;
    true ->
      Active = sets:add_element(U, maps:get(active_30d, Acc1)),
      Acc2 = Acc1#{active_30d => Active},
      Acc3 = case K of
        <<"confirm">> ->
          Cbu = maps:get(confirms_by_user_30d, Acc2),
          Acc2#{confirms_by_user_30d => maps:update_with(U, fun(V) -> V + N end, N, Cbu)};
        _ -> Acc2
      end,
      case K of
        <<"confirm">> ->
          Cbp = maps:get(confirms_by_pattern, Acc3),
          Acc3#{confirms_by_pattern => maps:update_with(P, fun(V) -> V + N end, N, Cbp)};
        _ -> Acc3
      end
  end.

ratio(_, 0) -> 0.0;
ratio(Part, Total) -> Part / Total.

%%%===================================================================
%%% Даты и rate-limit
%%%===================================================================

today() ->
  {{Y, M, D}, _} = calendar:universal_time(),
  iolist_to_binary(io_lib:format("~4..0B-~2..0B-~2..0B", [Y, M, D])).

shift_day(DayBin, Delta) ->
  <<Y:4/binary, "-", M:2/binary, "-", D:2/binary>> = DayBin,
  Date = {binary_to_integer(Y), binary_to_integer(M), binary_to_integer(D)},
  Sec = calendar:datetime_to_gregorian_seconds({Date, {0, 0, 0}}) + Delta * 86400,
  {{Y2, M2, D2}, _} = calendar:gregorian_seconds_to_datetime(Sec),
  iolist_to_binary(io_lib:format("~4..0B-~2..0B-~2..0B", [Y2, M2, D2])).

allow(UserId) ->
  ensure_rl(),
  Now = erlang:system_time(millisecond),
  Key = {rl, UserId},
  Result = case ets:lookup(?RL_TABLE, Key) of
    [{_, WindowStart, Count}] when Now - WindowStart < ?RL_WINDOW_MS ->
      Count < ?RL_LIMIT;
    _ ->
      true
  end,
  case Result of
    true ->
      ets:update_counter(?RL_TABLE, Key, {3, 1}, {Key, Now, 0}),
      true;
    false ->
      false
  end.

ensure_rl() ->
  case ets:info(?RL_TABLE) of
    undefined -> ets:new(?RL_TABLE, [named_table, public, set]);
    _ -> ok
  end,
  ok.