State machine ideas

pub struct PlayerFsm {
    default: Default,
    special: Special,
    current_state: PlayerStateName,
    next_state: Option<PlayerStateName>,

    pub blackboard: PlayerStateBlackboard,
}

pub struct Default {
    speed: f32,
}

pub struct Special {
    happiness: i32,
}

pub struct PlayerStateBlackboard {
    pub going_to_happiness: bool,
}

pub enum PlayerStateName {
    Default,
    Special,
}

impl PlayerFsm {
    pub fn change_state(&mut self, player_state_name: PlayerStateName) {
        self.next_state = Some(player_state_name);
    }

    pub fn tick(&mut self) -> Option<&mut dyn PlayerState> {
        if let Some(next_state) = self.next_state.take() {
            self.current_state = next_state;

            Some(self.state_mut())
        } else {
            None
        }
    }

    pub fn state_mut(&mut self) -> &mut dyn PlayerState {
        match self.current_state {
            PlayerStateName::Default => &mut self.default as &mut dyn PlayerState,
            PlayerStateName::Special => &mut self.special as &mut dyn PlayerState,
        }
    }
}

pub trait PlayerState {}

impl PlayerState for Default {}
impl PlayerState for Special {}