How to "split-or-other-pane"

[kyanagi]

I tried to add a key binding to following feature:

if the_tab_has_only_one_pane
  -- SplitHorizontal
else
  -- activate the "next" pane
end

There may be two problems to implement this.

(1) In an action callback, I can access to the window object and the pane object.
But I can't know how many panes are there in the tab.

(2) ActivatePaneDirection is not cyclic. (When I do ActivatePaneDirection="Right" on the rightmost pane, the active pane does not change.)

Does anyone have any good ideas?