💄 Only make Undo available if there are things to undo

Author: davep

src/complexitty/providers/main.py

@@ -85,7 +85,7 @@ def commands(self) -> CommandHits:
  yield SetColourToShadesOfBlue()
  yield SetColourToShadesOfGreen()
  yield SetColourToShadesOfRed()
- yield Undo()
+ yield from self.maybe(Undo)
  yield ZeroZero()
  yield ZoomIn()
  yield ZoomInFaster()

src/complexitty/screens/main.py

@@ -167,6 +167,27 @@ def on_mount(self) -> None:
  else get_colour_map(self._arguments.colour_map),
  )
 
+ def check_action(self, action: str, parameters: tuple[object, ...]) -> bool | None:
+ """Check if an action is possible to perform right now.
+
+ Args:
+ action: The action to perform.
+ parameters: The parameters of the action.
+
+ Returns:
+ `True` if it can perform, `False` or `None` if not.
+ """
+ if not self.is_mounted:
+ # Surprisingly it seems that Textual's "dynamic bindings" can
+ # cause this method to be called before the DOM is up and
+ # running. This breaks the rule of least astonishment, I'd say,
+ # but okay let's be defensive... (when I can come up with a nice
+ # little MRE I'll report it).
+ return True
+ if action == Undo.action_name():
+ return bool(self._history) or None
+ return True
+
  @on(Mandelbrot.Plotted)
  def _update_situation(self, message: Mandelbrot.Plotted) -> None:
  """Update the current situation after the latest plot.
@@ -206,6 +227,7 @@ def _remember(self) -> None:
  plot.multibrot,
  )
  )
+ self.refresh_bindings()
 
  def action_zoom(self, change: float) -> None:
  """Change the zoom value.
@@ -321,6 +343,7 @@ def action_undo_command(self) -> None:
  situation = self._history.pop()
  except IndexError:
  return
+ self.refresh_bindings()
  self.query_one(Mandelbrot).set(
  x_position=situation.x_position,
  y_position=situation.y_position,