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state.rs
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state.rs
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use crate::{Resource, Resources, Stage, System, SystemStage, World};
use bevy_utils::HashMap;
use std::{mem::Discriminant, ops::Deref};
use thiserror::Error;
pub(crate) struct StateStages {
update: Box<dyn Stage>,
enter: Box<dyn Stage>,
exit: Box<dyn Stage>,
}
impl Default for StateStages {
fn default() -> Self {
Self {
enter: Box::new(SystemStage::parallel()),
update: Box::new(SystemStage::parallel()),
exit: Box::new(SystemStage::parallel()),
}
}
}
pub struct StateStage<T> {
stages: HashMap<Discriminant<T>, StateStages>,
}
impl<T> Default for StateStage<T> {
fn default() -> Self {
Self {
stages: Default::default(),
}
}
}
#[allow(clippy::mem_discriminant_non_enum)]
impl<T> StateStage<T> {
pub fn with_enter_stage<S: Stage>(mut self, state: T, stage: S) -> Self {
self.set_enter_stage(state, stage);
self
}
pub fn with_exit_stage<S: Stage>(mut self, state: T, stage: S) -> Self {
self.set_exit_stage(state, stage);
self
}
pub fn with_update_stage<S: Stage>(mut self, state: T, stage: S) -> Self {
self.set_update_stage(state, stage);
self
}
pub fn set_enter_stage<S: Stage>(&mut self, state: T, stage: S) -> &mut Self {
let stages = self.state_stages(state);
stages.enter = Box::new(stage);
self
}
pub fn set_exit_stage<S: Stage>(&mut self, state: T, stage: S) -> &mut Self {
let stages = self.state_stages(state);
stages.exit = Box::new(stage);
self
}
pub fn set_update_stage<S: Stage>(&mut self, state: T, stage: S) -> &mut Self {
let stages = self.state_stages(state);
stages.update = Box::new(stage);
self
}
pub fn on_state_enter<S: System<In = (), Out = ()>>(
&mut self,
state: T,
system: S,
) -> &mut Self {
self.enter_stage(state, |system_stage: &mut SystemStage| {
system_stage.add_system(system)
})
}
pub fn on_state_exit<S: System<In = (), Out = ()>>(
&mut self,
state: T,
system: S,
) -> &mut Self {
self.exit_stage(state, |system_stage: &mut SystemStage| {
system_stage.add_system(system)
})
}
pub fn on_state_update<S: System<In = (), Out = ()>>(
&mut self,
state: T,
system: S,
) -> &mut Self {
self.update_stage(state, |system_stage: &mut SystemStage| {
system_stage.add_system(system)
})
}
pub fn enter_stage<S: Stage, F: FnOnce(&mut S) -> &mut S>(
&mut self,
state: T,
func: F,
) -> &mut Self {
let stages = self.state_stages(state);
func(
stages
.enter
.downcast_mut()
.expect("'Enter' stage does not match the given type"),
);
self
}
pub fn exit_stage<S: Stage, F: FnOnce(&mut S) -> &mut S>(
&mut self,
state: T,
func: F,
) -> &mut Self {
let stages = self.state_stages(state);
func(
stages
.exit
.downcast_mut()
.expect("'Exit' stage does not match the given type"),
);
self
}
pub fn update_stage<S: Stage, F: FnOnce(&mut S) -> &mut S>(
&mut self,
state: T,
func: F,
) -> &mut Self {
let stages = self.state_stages(state);
func(
stages
.update
.downcast_mut()
.expect("'Update' stage does not match the given type"),
);
self
}
fn state_stages(&mut self, state: T) -> &mut StateStages {
self.stages
.entry(std::mem::discriminant(&state))
.or_default()
}
}
#[allow(clippy::mem_discriminant_non_enum)]
impl<T: Resource + Clone> Stage for StateStage<T> {
fn initialize(&mut self, world: &mut World, resources: &mut Resources) {
for state_stages in self.stages.values_mut() {
state_stages.enter.initialize(world, resources);
state_stages.update.initialize(world, resources);
state_stages.exit.initialize(world, resources);
}
}
fn run(&mut self, world: &mut World, resources: &mut Resources) {
let current_stage = loop {
let (next_stage, current_stage) = {
let mut state = resources
.get_mut::<State<T>>()
.expect("Missing state resource");
let result = (
state.next.as_ref().map(|next| std::mem::discriminant(next)),
std::mem::discriminant(&state.current),
);
state.apply_next();
result
};
// if next_stage is Some, we just applied a new state
if let Some(next_stage) = next_stage {
if next_stage != current_stage {
if let Some(current_state_stages) = self.stages.get_mut(¤t_stage) {
current_state_stages.exit.run(world, resources);
}
}
if let Some(next_state_stages) = self.stages.get_mut(&next_stage) {
next_state_stages.enter.run(world, resources);
}
} else {
break current_stage;
}
};
if let Some(current_state_stages) = self.stages.get_mut(¤t_stage) {
current_state_stages.update.run(world, resources);
}
}
}
#[derive(Debug, Error)]
pub enum StateError {
#[error("Attempted to change the state to the current state.")]
AlreadyInState,
#[error("Attempted to queue a state change, but there was already a state queued.")]
StateAlreadyQueued,
}
#[derive(Debug)]
pub struct State<T: Clone> {
previous: Option<T>,
current: T,
next: Option<T>,
}
#[allow(clippy::mem_discriminant_non_enum)]
impl<T: Clone> State<T> {
pub fn new(state: T) -> Self {
Self {
current: state.clone(),
previous: None,
// add value to queue so that we "enter" the state
next: Some(state),
}
}
pub fn current(&self) -> &T {
&self.current
}
pub fn previous(&self) -> Option<&T> {
self.previous.as_ref()
}
pub fn next(&self) -> Option<&T> {
self.next.as_ref()
}
/// Queue a state change. This will fail if there is already a state in the queue, or if the given `state` matches the current state
pub fn set_next(&mut self, state: T) -> Result<(), StateError> {
if std::mem::discriminant(&self.current) == std::mem::discriminant(&state) {
return Err(StateError::AlreadyInState);
}
if self.next.is_some() {
return Err(StateError::StateAlreadyQueued);
}
self.next = Some(state);
Ok(())
}
/// Same as [Self::set_next], but if there is already a next state, it will be overwritten instead of failing
pub fn overwrite_next(&mut self, state: T) -> Result<(), StateError> {
if std::mem::discriminant(&self.current) == std::mem::discriminant(&state) {
return Err(StateError::AlreadyInState);
}
self.next = Some(state);
Ok(())
}
fn apply_next(&mut self) {
if let Some(next) = self.next.take() {
let previous = std::mem::replace(&mut self.current, next);
if std::mem::discriminant(&previous) != std::mem::discriminant(&self.current) {
self.previous = Some(previous)
}
}
}
}
impl<T: Clone> Deref for State<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
&self.current
}
}