feat(email): send booking reminders before event start.

Job process_reminders in subscription_worker; REMINDER_LEAD_HOURS window;
CalenTIQ email + in-app event_reminder; idempotent reminder_sent.
Refs EventHub/EventHubBack#70

src/logic/logic_booking.erl

@@ -7,7 +7,7 @@
   delete_booking/2,
   list_bookings_admin/0, get_booking_admin/1,
   list_event_bookings/1, list_event_bookings/2,
-  process_timeout_bookings/0, cancel_pending_for_owner/1,
+  process_timeout_bookings/0, process_reminders/0, cancel_pending_for_owner/1,
   cancel_pending_for_calendar/1]).
 
 %%%-------------------------------------------------------------------
@@ -367,6 +367,84 @@ process_timeout_bookings() ->
   lists:foreach(fun(B) -> maybe_timeout(B, NowSec) end, Pending),
   ok.
 
+%%%-------------------------------------------------------------------
+%%% @doc Email + in-app reminder before event start (Back#70).
+%%% Confirmed bookings with reminder_sent=false whose event starts within
+%%% REMINDER_LEAD_HOURS (default 24). Flag set before send (once).
+%%% @end
+%%%-------------------------------------------------------------------
+-spec process_reminders() -> ok.
+process_reminders() ->
+  NowSec = calendar:datetime_to_gregorian_seconds(calendar:universal_time()),
+  LeadSec = reminder_lead_hours() * 3600,
+  Horizon = NowSec + LeadSec,
+  Candidates = mnesia:dirty_match_object(
+    #booking{status = confirmed, reminder_sent = false, _ = '_'}),
+  lists:foreach(fun(B) -> maybe_remind(B, NowSec, Horizon) end, Candidates),
+  ok.
+
+maybe_remind(#booking{id = Id, event_id = EventId, user_id = UserId} = Booking,
+             NowSec, Horizon) ->
+  case core_event:get_by_id(EventId) of
+    {ok, #event{status = active, start_time = Start, title = Title,
+                calendar_id = CalId} = _Event} ->
+      StartSec = calendar:datetime_to_gregorian_seconds(Start),
+      case StartSec > NowSec andalso StartSec =< Horizon of
+        true ->
+          case core_booking:update(Id, [{reminder_sent, true}]) of
+            {ok, _} ->
+              send_reminder(UserId, Title, Start, CalId, EventId),
+              ok;
+            _ ->
+              ok
+          end;
+        false ->
+          ok
+      end;
+    _ ->
+      ok
+  end,
+  Booking.
+
+send_reminder(UserId, Title, Start, CalId, EventId) ->
+  Path = <<"/c/", CalId/binary, "/e/", EventId/binary>>,
+  WhenText = format_when(Start),
+  case core_user:get_by_id(UserId) of
+    {ok, #user{email = Email}} when is_binary(Email), Email =/= <<>> ->
+      _ = logic_email:send_booking_reminder(Email, Title, Start, Path);
+    _ ->
+      ok
+  end,
+  _ = logic_notification:notify_event_reminder(UserId, #{
+    event_id => EventId,
+    calendar_id => CalId,
+    title => Title,
+    start_time => Start,
+    when_text => WhenText
+  }),
+  ok.
+
+format_when({{Y, Mo, D}, {H, Mi, _S}}) ->
+  iolist_to_binary(io_lib:format("~4..0B-~2..0B-~2..0B ~2..0B:~2..0B",
+                                 [Y, Mo, D, H, Mi])).
+
+reminder_lead_hours() ->
+  case application:get_env(eventhub, reminder_lead_hours) of
+    {ok, N} when is_integer(N), N > 0 -> N;
+    _ ->
+      case os:getenv("REMINDER_LEAD_HOURS") of
+        false -> 24;
+        "" -> 24;
+        S ->
+          try list_to_integer(S) of
+            N when N > 0 -> N;
+            _ -> 24
+          catch
+            _:_ -> 24
+          end
+      end
+  end.
+
 maybe_timeout(#booking{id = Id, event_id = EventId, created_at = Created} = Booking, NowSec) ->
   case core_event:get_by_id(EventId) of
     {ok, Event} ->