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use bevy_utils::tracing::warn;
use crate::{
archetype::{Archetype, ArchetypeComponentId},
component::ComponentId,
query::Access,
world::World,
};
use std::borrow::Cow;
/// An ECS system that can be added to a [`Schedule`](crate::schedule::Schedule)
///
/// Systems are functions with all arguments implementing
/// [`SystemParam`](crate::system::SystemParam).
///
/// Systems are added to an application using `App::add_system(my_system)`
/// or similar methods, and will generally run once per pass of the main loop.
///
/// Systems are executed in parallel, in opportunistic order; data access is managed automatically.
/// It's possible to specify explicit execution order between specific systems,
/// see [`SystemDescriptor`](crate::schedule::SystemDescriptor).
pub trait System: Send + Sync + 'static {
/// The system's input. See [`In`](crate::system::In) for
/// [`FunctionSystem`](crate::system::FunctionSystem)s.
type In;
/// The system's output.
type Out;
/// Returns the system's name.
fn name(&self) -> Cow<'static, str>;
/// Register a new archetype for this system.
fn new_archetype(&mut self, archetype: &Archetype);
/// Returns the system's component [`Access`].
fn component_access(&self) -> &Access<ComponentId>;
/// Returns the system's archetype component [`Access`].
fn archetype_component_access(&self) -> &Access<ArchetypeComponentId>;
/// Returns true if the system is [`Send`].
fn is_send(&self) -> bool;
/// Runs the system with the given input in the world. Unlike [`System::run`], this function
/// takes a shared reference to [`World`] and may therefore break Rust's aliasing rules, making
/// it unsafe to call.
///
/// # Safety
///
/// This might access world and resources in an unsafe manner. This should only be called in one
/// of the following contexts:
/// 1. This system is the only system running on the given world across all threads.
/// 2. This system only runs in parallel with other systems that do not conflict with the
/// [`System::archetype_component_access()`].
unsafe fn run_unsafe(&mut self, input: Self::In, world: &World) -> Self::Out;
/// Runs the system with the given input in the world.
fn run(&mut self, input: Self::In, world: &mut World) -> Self::Out {
// SAFE: world and resources are exclusively borrowed
unsafe { self.run_unsafe(input, world) }
}
fn apply_buffers(&mut self, world: &mut World);
/// Initialize the system.
fn initialize(&mut self, _world: &mut World);
fn check_change_tick(&mut self, change_tick: u32);
}
/// A convenience type alias for a boxed [`System`] trait object.
pub type BoxedSystem<In = (), Out = ()> = Box<dyn System<In = In, Out = Out>>;
pub(crate) fn check_system_change_tick(
last_change_tick: &mut u32,
change_tick: u32,
system_name: &str,
) {
let tick_delta = change_tick.wrapping_sub(*last_change_tick);
const MAX_DELTA: u32 = (u32::MAX / 4) * 3;
// Clamp to max delta
if tick_delta > MAX_DELTA {
warn!(
"Too many intervening systems have run since the last time System '{}' was last run; it may fail to detect changes.",
system_name
);
*last_change_tick = change_tick.wrapping_sub(MAX_DELTA);
}
}