Calculate how many keystrokes were used in triggering this folder (if applicable).

def calculate_input(self, buffer):
        """
        Calculate how many keystrokes were used in triggering this folder (if applicable).
        """
        if TriggerMode.ABBREVIATION in self.modes and self.backspace:
            if self._should_trigger_abbreviation(buffer):
                if self.immediate:
                    return len(self._get_trigger_abbreviation(buffer))
                else:
                    return len(self._get_trigger_abbreviation(buffer)) + 1

        if self.parent is not None:
            return self.parent.calculate_input(buffer)

        return 0