bevy/crates/bevy_ecs/src/system/adapter_system.rs

use std::borrow::Cow;

use super::{ReadOnlySystem, System};
use crate::world::unsafe_world_cell::UnsafeWorldCell;

/// Customizes the behavior of an [`AdapterSystem`]
///
/// # Examples
///
/// ```
/// # use bevy_ecs::prelude::*;
/// use bevy_ecs::system::{Adapt, AdapterSystem};
///
/// // A system adapter that inverts the result of a system.
/// // NOTE: Instead of manually implementing this, you can just use `bevy_ecs::schedule::common_conditions::not`.
/// pub type NotSystem<S> = AdapterSystem<NotMarker, S>;
///
/// // This struct is used to customize the behavior of our adapter.
/// pub struct NotMarker;
///
/// impl<S> Adapt<S> for NotMarker
/// where
///     S: System,
///     S::Out: std::ops::Not,
/// {
///     type In = S::In;
///     type Out = <S::Out as std::ops::Not>::Output;
///
///     fn adapt(
///         &mut self,
///         input: Self::In,
///         run_system: impl FnOnce(S::In) -> S::Out,
///     ) -> Self::Out {
///         !run_system(input)
///     }
/// }
/// # let mut world = World::new();
/// # let mut system = NotSystem::new(NotMarker, IntoSystem::into_system(|| false), "".into());
/// # system.initialize(&mut world);
/// # assert!(system.run((), &mut world));
/// ```
pub trait Adapt<S: System>: Send + Sync + 'static {
    /// The [input](System::In) type for an [`AdapterSystem`].
    type In;
    /// The [output](System::Out) type for an [`AdapterSystem`].
    type Out;

    /// When used in an [`AdapterSystem`], this function customizes how the system
    /// is run and how its inputs/outputs are adapted.
    fn adapt(&mut self, input: Self::In, run_system: impl FnOnce(S::In) -> S::Out) -> Self::Out;
}

/// A [`System`] that takes the output of `S` and transforms it by applying `Func` to it.
#[derive(Clone)]
pub struct AdapterSystem<Func, S> {
    func: Func,
    system: S,
    name: Cow<'static, str>,
}

impl<Func, S> AdapterSystem<Func, S>
where
    Func: Adapt<S>,
    S: System,
{
    /// Creates a new [`System`] that uses `func` to adapt `system`, via the [`Adapt`] trait.
    pub const fn new(func: Func, system: S, name: Cow<'static, str>) -> Self {
        Self { func, system, name }
    }
}

impl<Func, S> System for AdapterSystem<Func, S>
where
    Func: Adapt<S>,
    S: System,
{
    type In = Func::In;
    type Out = Func::Out;

    fn name(&self) -> Cow<'static, str> {
        self.name.clone()
    }

    fn type_id(&self) -> std::any::TypeId {
        std::any::TypeId::of::<Self>()
    }

    fn component_access(&self) -> &crate::query::Access<crate::component::ComponentId> {
        self.system.component_access()
    }

    #[inline]
    fn archetype_component_access(
        &self,
    ) -> &crate::query::Access<crate::archetype::ArchetypeComponentId> {
        self.system.archetype_component_access()
    }

    fn is_send(&self) -> bool {
        self.system.is_send()
    }

    fn is_exclusive(&self) -> bool {
        self.system.is_exclusive()
    }

    #[inline]
    unsafe fn run_unsafe(&mut self, input: Self::In, world: UnsafeWorldCell) -> Self::Out {
        // SAFETY: `system.run_unsafe` has the same invariants as `self.run_unsafe`.
        self.func
            .adapt(input, |input| self.system.run_unsafe(input, world))
    }

    #[inline]
    fn run(&mut self, input: Self::In, world: &mut crate::prelude::World) -> Self::Out {
        self.func
            .adapt(input, |input| self.system.run(input, world))
    }

    #[inline]
    fn apply_deferred(&mut self, world: &mut crate::prelude::World) {
        self.system.apply_deferred(world);
    }

    fn initialize(&mut self, world: &mut crate::prelude::World) {
        self.system.initialize(world);
    }

    #[inline]
    fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
        self.system.update_archetype_component_access(world);
    }

    fn check_change_tick(&mut self, change_tick: crate::component::Tick) {
        self.system.check_change_tick(change_tick);
    }

    fn get_last_run(&self) -> crate::component::Tick {
        self.system.get_last_run()
    }

    fn set_last_run(&mut self, last_run: crate::component::Tick) {
        self.system.set_last_run(last_run);
    }

    fn default_system_sets(&self) -> Vec<Box<dyn crate::schedule::SystemSet>> {
        self.system.default_system_sets()
    }
}

// SAFETY: The inner system is read-only.
unsafe impl<Func, S> ReadOnlySystem for AdapterSystem<Func, S>
where
    Func: Adapt<S>,
    S: ReadOnlySystem,
{
}

impl<F, S, Out> Adapt<S> for F
where
    S: System,
    F: Send + Sync + 'static + FnMut(S::Out) -> Out,
{
    type In = S::In;
    type Out = Out;

    fn adapt(&mut self, input: S::In, run_system: impl FnOnce(S::In) -> S::Out) -> Out {
        self(run_system(input))
    }
}