How to implement a hotkey to toggle background opacity

[ackerr]

I find some options to change background opacity, but it need two different hotkey to implement toggle

map super+u           set_background_opacity 1
map super+shift+u set_background_opacity default

In wezterm, i can write a lua function implement it

wezterm.on("toggle-opacity", function(window, _)
  local overrides = window:get_config_overrides() or {}
  if not overrides.window_background_opacity then
    overrides.window_background_opacity = 0.8
    overrides.text_background_opacity = 0.8
  else
    overrides.window_background_opacity = nil
    overrides.text_background_opacity = nil
  end
  window:set_config_overrides(overrides)
end)

Although I have found a way to implement custom scripts with kitten, but I am not familiar with the APIs inside and don't know where to start.

Can you give some hints?

[kovidgoyal]

Write a kitten

https://sw.kovidgoyal.net/kitty/kittens/custom/#using-kittens-to-script-kitty-without-any-terminal-ui

something like

def handle_result(args, answer, target_window_id, boss): 
    import kitty.fast_data_types as f
    os_window_id = f.current_focused_os_window_id()
    current_opacity = f.background_opacity_of(os_window_id)
    boss.set_background_opacity("default" if current_opacity == whatever else whatever)