enums+window: make GcalWindowView iterators order and length agnostic

Currently, iterators over the GcalWindowView enum relied
on knowing the first and last enum value. But we know,
without knowing which is the first, that an enum in C
will assign 0 to its first value if not otherwise
specified.

And with the trick of a new end value similar to N_PROPS,
we can determine the amount of available window views
without relying on know which it is.

Signed-off-by: Markus Göllnitz <camelcasenick@bewares.it>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/542>

src/gcal-enums.h

@@ -42,6 +42,8 @@ typedef enum
 {
   GCAL_WINDOW_VIEW_WEEK,
   GCAL_WINDOW_VIEW_MONTH,
+
+  GCAL_WINDOW_VIEW_N_VIEWS,
 } GcalWindowView;
 
 typedef enum

src/gui/gcal-window.c

@@ -261,7 +261,7 @@ update_active_date (GcalWindow *window,
 
   gcal_set_date_time (&window->active_date, new_date);
 
-  for (i = GCAL_WINDOW_VIEW_WEEK; i <= GCAL_WINDOW_VIEW_MONTH; i++)
+  for (i = 0; i < GCAL_WINDOW_VIEW_N_VIEWS; i++)
     gcal_view_set_date (GCAL_VIEW (window->views[i]), new_date);
   gcal_view_set_date (GCAL_VIEW (window->agenda_view), new_date);
   gcal_view_set_date (GCAL_VIEW (window->date_chooser), new_date);
@@ -452,7 +452,7 @@ on_view_action_activated (GSimpleAction *action,
   else if (view == -2)
     view = --(window->active_view);
 
-  window->active_view = CLAMP (view, GCAL_WINDOW_VIEW_WEEK, GCAL_WINDOW_VIEW_MONTH);
+  window->active_view = CLAMP (view, 0, GCAL_WINDOW_VIEW_N_VIEWS - 1);
   adw_view_stack_set_visible_child (window->views_stack, window->views[window->active_view]);
 
   g_object_notify_by_pspec (G_OBJECT (user_data), properties[PROP_ACTIVE_VIEW]);