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use std::ops::Deref;
use bevy_ecs::{
change_detection::DetectChangesMut,
system::{ResMut, Resource},
world::{FromWorld, World},
};
use super::{freely_mutable_state::FreelyMutableState, states::States};
#[cfg(feature = "bevy_reflect")]
use bevy_ecs::prelude::ReflectResource;
/// A finite-state machine whose transitions have associated schedules
/// ([`OnEnter(state)`](crate::state::OnEnter) and [`OnExit(state)`](crate::state::OnExit)).
///
/// The current state value can be accessed through this resource. To *change* the state,
/// queue a transition in the [`NextState<S>`] resource, and it will be applied during the
/// [`StateTransition`](crate::transition::StateTransition) schedule - which by default runs after `PreUpdate`.
///
/// You can also manually trigger the [`StateTransition`](crate::transition::StateTransition) schedule to apply the changes
/// at an arbitrary time.
///
/// The starting state is defined via the [`Default`] implementation for `S`.
///
/// ```
/// use bevy_state::prelude::*;
/// use bevy_ecs::prelude::*;
/// use bevy_state_macros::States;
///
/// #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, Default, States)]
/// enum GameState {
/// #[default]
/// MainMenu,
/// SettingsMenu,
/// InGame,
/// }
///
/// fn game_logic(game_state: Res<State<GameState>>) {
/// match game_state.get() {
/// GameState::InGame => {
/// // Run game logic here...
/// },
/// _ => {},
/// }
/// }
/// ```
#[derive(Resource, Debug)]
#[cfg_attr(
feature = "bevy_reflect",
derive(bevy_reflect::Reflect),
reflect(Resource)
)]
pub struct State<S: States>(pub(crate) S);
impl<S: States> State<S> {
/// Creates a new state with a specific value.
///
/// To change the state use [`NextState<S>`] rather than using this to modify the `State<S>`.
pub fn new(state: S) -> Self {
Self(state)
}
/// Get the current state.
pub fn get(&self) -> &S {
&self.0
}
}
impl<S: States + FromWorld> FromWorld for State<S> {
fn from_world(world: &mut World) -> Self {
Self(S::from_world(world))
}
}
impl<S: States> PartialEq<S> for State<S> {
fn eq(&self, other: &S) -> bool {
self.get() == other
}
}
impl<S: States> Deref for State<S> {
type Target = S;
fn deref(&self) -> &Self::Target {
self.get()
}
}
/// The next state of [`State<S>`].
///
/// This can be fetched as a resource and used to queue state transitions.
/// To queue a transition, call [`NextState::set`] or mutate the value to [`NextState::Pending`] directly.
///
/// Note that these transitions can be overridden by other systems:
/// only the actual value of this resource during the [`StateTransition`](crate::transition::StateTransition) schedule matters.
///
/// ```
/// use bevy_state::prelude::*;
/// use bevy_ecs::prelude::*;
///
/// #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, Default, States)]
/// enum GameState {
/// #[default]
/// MainMenu,
/// SettingsMenu,
/// InGame,
/// }
///
/// fn start_game(mut next_game_state: ResMut<NextState<GameState>>) {
/// next_game_state.set(GameState::InGame);
/// }
/// ```
#[derive(Resource, Debug, Default, Clone)]
#[cfg_attr(
feature = "bevy_reflect",
derive(bevy_reflect::Reflect),
reflect(Resource)
)]
pub enum NextState<S: FreelyMutableState> {
/// No state transition is pending
#[default]
Unchanged,
/// There is a pending transition for state `S`
Pending(S),
}
impl<S: FreelyMutableState> NextState<S> {
/// Tentatively set a pending state transition to `Some(state)`.
pub fn set(&mut self, state: S) {
*self = Self::Pending(state);
}
/// Remove any pending changes to [`State<S>`]
pub fn reset(&mut self) {
*self = Self::Unchanged;
}
}
pub(crate) fn take_next_state<S: FreelyMutableState>(
next_state: Option<ResMut<NextState<S>>>,
) -> Option<S> {
let mut next_state = next_state?;
match std::mem::take(next_state.bypass_change_detection()) {
NextState::Pending(x) => {
next_state.set_changed();
Some(x)
}
NextState::Unchanged => None,
}
}