fix(recurrence): honor BYDAY for weekly RRULE expansion

Expand weekdays in the DTSTART week and advance by Interval weeks from Monday;
add unit coverage for MO/WE/FR and mid-week starts.

src/logic/logic_recurrence.erl

@@ -106,15 +106,21 @@ generate_by_freq(Current, ?FREQ_WEEKLY, Interval, ByDay, EndBoundary, MaxCount,
   case should_stop(Current, EndBoundary, MaxCount, Count) of
     true -> lists:reverse(Acc);
     false ->
-      % Если указаны дни недели, генерируем только в эти дни
-      NewOccurrences = case ByDay of
-                         [] -> [Current];
-                         Days -> filter_by_weekday(Current, Days)
-                       end,
+      {NewOccurrences, Next} =
+        case ByDay of
+          [] ->
+            {[Current], add_weeks(Current, Interval)};
+          Days ->
+            %% BYDAY: expand weekdays in Current's week (on/after Current),
+            %% then jump Interval weeks from that week's Monday.
+            Occs = [O || O <- filter_by_weekday(Current, Days), O =< EndBoundary],
+            {Occs, add_weeks(week_start_monday(Current), Interval)}
+        end,
+      %% Prepend reversed batch so final lists:reverse/1 yields chronological order.
       generate_by_freq(
-        add_weeks(Current, Interval),
+        Next,
         ?FREQ_WEEKLY, Interval, ByDay, EndBoundary, MaxCount,
-        Count + 1, NewOccurrences ++ Acc
+        Count + 1, lists:reverse(NewOccurrences) ++ Acc
       )
   end;
 
@@ -151,9 +157,56 @@ add_months({{Y, M, D}, Time}, N) ->
   NewDay = minus(D, calendar:last_day_of_the_month(NewYear, NewMonth)),
   {{NewYear, NewMonth, NewDay}, Time}.
 
-filter_by_weekday(DateTime, _Days) ->
-  % Упрощённая версия — всегда возвращаем текущую дату
-  % В полной версии нужно проверять день недели
+%% BYDAY codes (RFC 5545): MO..SU. calendar:day_of_the_week = 1=Mon .. 7=Sun.
+week_start_monday({{Y, M, D}, Time}) ->
+  Dow = calendar:day_of_the_week({Y, M, D}),
+  add_days({{Y, M, D}, Time}, -(Dow - 1)).
+
+byday_to_dow(<<"MO">>) -> 1;
+byday_to_dow(<<"TU">>) -> 2;
+byday_to_dow(<<"WE">>) -> 3;
+byday_to_dow(<<"TH">>) -> 4;
+byday_to_dow(<<"FR">>) -> 5;
+byday_to_dow(<<"SA">>) -> 6;
+byday_to_dow(<<"SU">>) -> 7;
+byday_to_dow("MO") -> 1;
+byday_to_dow("TU") -> 2;
+byday_to_dow("WE") -> 3;
+byday_to_dow("TH") -> 4;
+byday_to_dow("FR") -> 5;
+byday_to_dow("SA") -> 6;
+byday_to_dow("SU") -> 7;
+byday_to_dow(mo) -> 1;
+byday_to_dow(tu) -> 2;
+byday_to_dow(we) -> 3;
+byday_to_dow(th) -> 4;
+byday_to_dow(fr) -> 5;
+byday_to_dow(sa) -> 6;
+byday_to_dow(su) -> 7;
+byday_to_dow(_) -> undefined.
+
+%% Occurrences for BYDAY in the week of Current, same time-of-day.
+%% Only dates on or after Current (so DTSTART mid-week does not emit earlier weekdays).
+filter_by_weekday(Current, Days) when is_list(Days) ->
+  Monday = week_start_monday(Current),
+  Occs =
+    lists:foldl(
+      fun(DayCode, Acc) ->
+        case byday_to_dow(DayCode) of
+          undefined -> Acc;
+          TargetDow ->
+            Occ = add_days(Monday, TargetDow - 1),
+            case Occ >= Current of
+              true -> [Occ | Acc];
+              false -> Acc
+            end
+        end
+      end,
+      [],
+      Days
+    ),
+  lists:sort(Occs);
+filter_by_weekday(DateTime, _) ->
   [DateTime].
 
 filter_by_month_day(DateTime, _Days) ->