freecs 3.21.1

//! System-parameter functions over [`DynWorld`]: functions whose
//! arguments are [`Res`], [`ResMut`], and [`Query`] resolve into runnable
//! systems the existing [`Schedule`] accepts, with no
//! `unsafe` and no new executor.
//!
//! A system is any function whose parameters are system parameters. Register
//! it on a [`Schedule`] over a [`DynWorld`] with
//! [`ScheduleExt::add_system`]:
//!
//! ```rust
//! use freecs::Schedule;
//! use freecs::dynamic::DynWorld;
//! use freecs::system_param::{Query, Res, ResMut, ScheduleExt};
//!
//! #[derive(Default, Clone, Debug)]
//! struct Position { x: f32, y: f32 }
//! #[derive(Default, Clone, Debug)]
//! struct Velocity { x: f32, y: f32 }
//!
//! struct DeltaTime(f32);
//! struct Score(u32);
//!
//! fn movement(dt: Res<DeltaTime>, mut score: ResMut<Score>, query: Query<(&mut Position, &Velocity)>) {
//!     query.for_each(|_entity, (position, velocity)| {
//!         position.x += velocity.x * dt.0;
//!         position.y += velocity.y * dt.0;
//!     });
//!     score.0 += 1;
//! }
//!
//! let mut world = DynWorld::new();
//! world.insert_resource(DeltaTime(0.5));
//! world.insert_resource(Score(0));
//! world.spawn((Position { x: 0.0, y: 0.0 }, Velocity { x: 2.0, y: 4.0 }));
//!
//! let mut schedule = Schedule::new();
//! schedule.add_system("movement", movement);
//! schedule.run(&mut world);
//!
//! assert_eq!(world.resource::<Score>().unwrap().0, 1);
//! ```
//!
//! Resource parameters ([`Res`], [`ResMut`]) resolve out of the world's
//! [`ResourceMap`](crate::dynamic::ResourceMap) through the same take/put
//! scope [`resources_scope`](crate::dynamic::ResourceHostExt::resources_scope)
//! uses, so they never alias a query's table borrow. Resource parameters
//! come first, query parameters after.
//!
//! A single query parameter borrows the world directly and pays nothing
//! beyond the query itself. Several query parameters in one system, such as
//! `fn(a: Query<&mut Position>, b: Query<&Velocity>)`, share the world
//! through a cell and each take it only for the span of one
//! [`for_each`](Query::for_each), so the cost is one borrow check per call
//! rather than anything per entity. Because `for_each` consumes the query,
//! two of them run in sequence, never nested. Type-level filters ([`With`],
//! [`Without`], [`Changed`], [`Added`], [`WithTag`], [`WithoutTag`], and
//! tuples of them) narrow a query as `Query<(&mut Position,), With<Player>>`.
//! [`ParamSet`] groups queries behind `p0()`/`p1()` accessors when you would
//! rather name a set than list the queries.
//!
//! ```rust
//! use freecs::dynamic::DynWorld;
//! use freecs::system_param::{Query, ScheduleExt};
//!
//! #[derive(Default, Clone, Debug)]
//! struct Position { x: f32, y: f32 }
//! #[derive(Default, Clone, Debug)]
//! struct Velocity { x: f32, y: f32 }
//!
//! fn drift(positions: Query<&mut Position>, velocities: Query<&Velocity>) {
//!     let mut total = (0.0, 0.0);
//!     velocities.for_each(|_entity, velocity| {
//!         total.0 += velocity.x;
//!         total.1 += velocity.y;
//!     });
//!     positions.for_each(|_entity, position| {
//!         position.x += total.0;
//!         position.y += total.1;
//!     });
//! }
//!
//! let mut world = DynWorld::new();
//! world.spawn((Position { x: 0.0, y: 0.0 }, Velocity { x: 1.0, y: 2.0 }));
//!
//! let mut schedule = freecs::Schedule::new();
//! schedule.add_system("drift", drift);
//! schedule.run(&mut world);
//!
//! assert_eq!(world.get::<Position>(world.query_ref::<&Position>().single().unwrap().0).unwrap().x, 1.0);
//! ```

use crate::Entity;
use crate::Schedule;
use crate::dynamic::{DynQuery, DynWorld, QueryTuple};
use std::cell::RefCell;
use std::marker::PhantomData;

/// A shared reference to a resource of type `T`, resolved for a system
/// parameter. Dereferences to `T`.
pub struct Res<'world, T> {
    value: &'world T,
}

impl<T> std::ops::Deref for Res<'_, T> {
    type Target = T;
    fn deref(&self) -> &T {
        self.value
    }
}

/// An exclusive reference to a resource of type `T`, resolved for a system
/// parameter. Dereferences to `T` and, mutably, writes through to it.
pub struct ResMut<'world, T> {
    value: &'world mut T,
}

impl<T> std::ops::Deref for ResMut<'_, T> {
    type Target = T;
    fn deref(&self) -> &T {
        self.value
    }
}

impl<T> std::ops::DerefMut for ResMut<'_, T> {
    fn deref_mut(&mut self) -> &mut T {
        self.value
    }
}

/// A resource system parameter: [`Res`] or [`ResMut`]. Each names one
/// resource type, taken out of the world's map for the system call and put
/// back afterward.
pub trait ResourceParam {
    /// The resource type this parameter reads.
    type Resource: Send + Sync + 'static;
    /// The parameter value handed to the system for a given borrow.
    type Item<'world>;
    /// Wraps the taken-out resource as the parameter value.
    fn build(resource: &mut Self::Resource) -> Self::Item<'_>;
}

impl<'a, T: Send + Sync + 'static> ResourceParam for Res<'a, T> {
    type Resource = T;
    type Item<'world> = Res<'world, T>;
    fn build(resource: &mut T) -> Res<'_, T> {
        Res { value: resource }
    }
}

impl<'a, T: Send + Sync + 'static> ResourceParam for ResMut<'a, T> {
    type Resource = T;
    type Item<'world> = ResMut<'world, T>;
    fn build(resource: &mut T) -> ResMut<'_, T> {
        ResMut { value: resource }
    }
}

/// A type-level query filter: [`With`], [`Without`], [`Changed`], [`Added`],
/// the unit type for no filter, or a tuple of filters applied in order.
pub trait QueryFilter {
    /// Applies this filter to a query builder.
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q>;
}

impl QueryFilter for () {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query
    }
}

/// Restricts a query to entities that also carry component `T`, without
/// fetching it.
pub struct With<T>(PhantomData<fn() -> T>);

impl<T: Send + Sync + Default + 'static> QueryFilter for With<T> {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query.with::<T>()
    }
}

/// Restricts a query to entities that do not carry component `T`.
pub struct Without<T>(PhantomData<fn() -> T>);

impl<T: Send + Sync + Default + 'static> QueryFilter for Without<T> {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query.without::<T>()
    }
}

/// Restricts a query to entities whose component `T` changed since the last
/// step. `T` must appear in the query tuple.
pub struct Changed<T>(PhantomData<fn() -> T>);

impl<T: Send + Sync + Default + 'static> QueryFilter for Changed<T> {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query.changed::<T>()
    }
}

/// Restricts a query to entities that gained component `T` since the last
/// step. `T` must appear in the query tuple.
pub struct Added<T>(PhantomData<fn() -> T>);

impl<T: Send + Sync + Default + 'static> QueryFilter for Added<T> {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query.added::<T>()
    }
}

/// Restricts a query to entities carrying the marker tag type `T`.
pub struct WithTag<T>(PhantomData<fn() -> T>);

impl<T: 'static> QueryFilter for WithTag<T> {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query.with_tag_type::<T>()
    }
}

/// Restricts a query to entities not carrying the marker tag type `T`.
pub struct WithoutTag<T>(PhantomData<fn() -> T>);

impl<T: 'static> QueryFilter for WithoutTag<T> {
    fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
        query.without_tag_type::<T>()
    }
}

macro_rules! impl_query_filter_tuple {
    ($($filter:ident),+) => {
        impl<$($filter: QueryFilter),+> QueryFilter for ($($filter,)+) {
            fn apply<Q: QueryTuple>(query: DynQuery<'_, Q>) -> DynQuery<'_, Q> {
                $(let query = $filter::apply(query);)+
                query
            }
        }
    };
}

impl_query_filter_tuple!(A);
impl_query_filter_tuple!(A, B);
impl_query_filter_tuple!(A, B, C);
impl_query_filter_tuple!(A, B, C, D);

enum QueryState<'world, Q: QueryTuple> {
    Eager(DynQuery<'world, Q>),
    Lazy(&'world RefCell<&'world mut DynWorld>),
}

/// A query system parameter over tuple `Q` with type-level filter `F`. The
/// filter defaults to none. A single query parameter borrows the world
/// directly; several query parameters in one system share the world through
/// a cell and take it one [`for_each`](Self::for_each) at a time.
pub struct Query<'world, Q: QueryTuple, F: QueryFilter = ()> {
    state: QueryState<'world, Q>,
    filter: PhantomData<fn() -> F>,
}

impl<'world, Q: QueryTuple, F: QueryFilter> Query<'world, Q, F> {
    /// Visits every matching entity with its fetched components.
    pub fn for_each(self, f: impl for<'item> FnMut(Entity, Q::Item<'item>)) {
        match self.state {
            QueryState::Eager(query) => F::apply(query).for_each(f),
            QueryState::Lazy(cell) => {
                let mut guard = cell.borrow_mut();
                let world: &mut DynWorld = &mut guard;
                F::apply(world.query::<Q>()).for_each(f);
            }
        }
    }

    /// The parallel form of [`for_each`](Self::for_each), table-granular.
    #[cfg(not(target_family = "wasm"))]
    pub fn par_for_each<Fun>(self, f: Fun)
    where
        Fun: for<'item> Fn(Entity, Q::Item<'item>) + Send + Sync,
    {
        match self.state {
            QueryState::Eager(query) => F::apply(query).par_for_each(f),
            QueryState::Lazy(cell) => {
                let mut guard = cell.borrow_mut();
                let world: &mut DynWorld = &mut guard;
                F::apply(world.query::<Q>()).par_for_each(f);
            }
        }
    }
}

/// A world-borrowing system parameter in the single-query slot, resolved
/// after the resource parameters are lifted out. Implemented for [`Query`]
/// and [`ParamSet`].
pub trait WorldParam {
    /// The parameter value handed to the system for a given borrow.
    type Item<'world>;
    /// Resolves the parameter against the world.
    fn build(world: &mut DynWorld) -> Self::Item<'_>;
}

impl<'a, Q: QueryTuple, F: QueryFilter> WorldParam for Query<'a, Q, F> {
    type Item<'world> = Query<'world, Q, F>;
    fn build(world: &mut DynWorld) -> Query<'_, Q, F> {
        Query {
            state: QueryState::Eager(world.query::<Q>()),
            filter: PhantomData,
        }
    }
}

/// A query parameter that shares the world with sibling query parameters
/// through a cell, so a system can take several [`Query`] arguments. Each
/// query borrows the world only for the span of one
/// [`for_each`](Query::for_each), so two queries never iterate at once.
pub trait MultiQueryParam {
    /// The parameter value handed to the system for a given borrow.
    type Item<'world>;
    /// Resolves the parameter against the shared world cell.
    fn build_lazy<'world>(cell: &'world RefCell<&'world mut DynWorld>) -> Self::Item<'world>;
}

impl<'a, Q: QueryTuple, F: QueryFilter> MultiQueryParam for Query<'a, Q, F> {
    type Item<'world> = Query<'world, Q, F>;
    fn build_lazy<'world>(cell: &'world RefCell<&'world mut DynWorld>) -> Query<'world, Q, F> {
        Query {
            state: QueryState::Lazy(cell),
            filter: PhantomData,
        }
    }
}

/// A set of conflicting query parameters accessed one at a time. Holds the
/// world and lends each member query through [`p0`](Self::p0),
/// [`p1`](Self::p1), and so on, so two mutable queries never live at once.
pub struct ParamSet<'world, T> {
    world: &'world mut DynWorld,
    marker: PhantomData<fn() -> T>,
}

impl<'a, T: 'static> WorldParam for ParamSet<'a, T>
where
    ParamSet<'a, T>: ParamSetAccess,
{
    type Item<'world> = ParamSet<'world, T>;
    fn build(world: &mut DynWorld) -> ParamSet<'_, T> {
        ParamSet {
            world,
            marker: PhantomData,
        }
    }
}

/// Marks the [`ParamSet`] tuples that expose member accessors.
pub trait ParamSetAccess {}

impl<P0: WorldParam, P1: WorldParam> ParamSetAccess for ParamSet<'_, (P0, P1)> {}

impl<'world, P0: WorldParam, P1: WorldParam> ParamSet<'world, (P0, P1)> {
    /// Borrows the world for the first member query.
    pub fn p0(&mut self) -> P0::Item<'_> {
        P0::build(self.world)
    }

    /// Borrows the world for the second member query.
    pub fn p1(&mut self) -> P1::Item<'_> {
        P1::build(self.world)
    }
}

impl<P0: WorldParam, P1: WorldParam, P2: WorldParam> ParamSetAccess for ParamSet<'_, (P0, P1, P2)> {}

impl<'world, P0: WorldParam, P1: WorldParam, P2: WorldParam> ParamSet<'world, (P0, P1, P2)> {
    /// Borrows the world for the first member query.
    pub fn p0(&mut self) -> P0::Item<'_> {
        P0::build(self.world)
    }

    /// Borrows the world for the second member query.
    pub fn p1(&mut self) -> P1::Item<'_> {
        P1::build(self.world)
    }

    /// Borrows the world for the third member query.
    pub fn p2(&mut self) -> P2::Item<'_> {
        P2::build(self.world)
    }
}

/// Converts a system-parameter function into a runner the
/// [`Schedule`] accepts. `Marker` is inferred from the
/// function's parameter types, so a plain `fn(Res<A>, ResMut<B>, Query<C>)`
/// registers directly. Register through [`ScheduleExt::add_system`].
pub trait IntoSystem<Marker>: Sized {
    /// Wraps the function into a closure that resolves its parameters from
    /// the world on each call.
    fn into_runner(self) -> impl FnMut(&mut DynWorld) + Send + 'static;
}

/// Registers system-parameter functions on a [`Schedule`]
/// over a [`DynWorld`], resolving [`Res`]/[`ResMut`]/[`Query`] parameters
/// per run.
pub trait ScheduleExt {
    /// Adds a system-parameter function under `name`, like
    /// [`Schedule::push`](crate::Schedule::push) for plain systems.
    fn add_system<Marker>(
        &mut self,
        name: &'static str,
        system: impl IntoSystem<Marker>,
    ) -> &mut Self;
}

impl ScheduleExt for Schedule<DynWorld> {
    fn add_system<Marker>(
        &mut self,
        name: &'static str,
        system: impl IntoSystem<Marker>,
    ) -> &mut Self {
        self.push(name, system.into_runner())
    }
}

/// The marker for a system whose parameters are all resources.
pub struct ResourceSystemMarker<R>(PhantomData<fn() -> R>);

/// The marker for a system with resource parameters and one trailing
/// world-borrowing parameter.
pub struct QuerySystemMarker<R, Q>(PhantomData<fn() -> (R, Q)>);

impl<Func, Q> IntoSystem<QuerySystemMarker<(), Q>> for Func
where
    Q: WorldParam,
    Func: FnMut(Q) + for<'world> FnMut(Q::Item<'world>) + Send + 'static,
{
    fn into_runner(mut self) -> impl FnMut(&mut DynWorld) + Send + 'static {
        move |world: &mut DynWorld| {
            let query = Q::build(world);
            self(query);
        }
    }
}

macro_rules! impl_resource_system {
    ($($resource:ident $binding:ident),+) => {
        impl<Func, $($resource,)+> IntoSystem<ResourceSystemMarker<($($resource,)+)>>
            for Func
        where
            $($resource: ResourceParam,)+
            Func: FnMut($($resource,)+)
                + for<'world> FnMut($($resource::Item<'world>,)+)
                + Send
                + 'static,
        {
            #[allow(non_snake_case)]
            fn into_runner(mut self) -> impl FnMut(&mut DynWorld) + Send + 'static {
                move |world: &mut DynWorld| {
                    world.resources_scope::<($($resource::Resource,)+), _>(|_world, bundle| {
                        let ($($binding,)+) = bundle;
                        self($($resource::build($binding),)+);
                    });
                }
            }
        }
    };
}

macro_rules! impl_query_system {
    ($($resource:ident $binding:ident),+) => {
        impl<Func, $($resource,)+ Q>
            IntoSystem<QuerySystemMarker<($($resource,)+), Q>> for Func
        where
            $($resource: ResourceParam,)+
            Q: WorldParam,
            Func: FnMut($($resource,)+ Q)
                + for<'world> FnMut($($resource::Item<'world>,)+ Q::Item<'world>)
                + Send
                + 'static,
        {
            #[allow(non_snake_case)]
            fn into_runner(mut self) -> impl FnMut(&mut DynWorld) + Send + 'static {
                move |world: &mut DynWorld| {
                    world.resources_scope::<($($resource::Resource,)+), _>(|world, bundle| {
                        let ($($binding,)+) = bundle;
                        let query = Q::build(world);
                        self($($resource::build($binding),)+ query);
                    });
                }
            }
        }
    };
}

impl_resource_system!(R0 r0);
impl_resource_system!(R0 r0, R1 r1);
impl_resource_system!(R0 r0, R1 r1, R2 r2);
impl_resource_system!(R0 r0, R1 r1, R2 r2, R3 r3);
impl_resource_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4);
impl_resource_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4, R5 r5);
impl_resource_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4, R5 r5, R6 r6);
impl_resource_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4, R5 r5, R6 r6, R7 r7);

impl_query_system!(R0 r0);
impl_query_system!(R0 r0, R1 r1);
impl_query_system!(R0 r0, R1 r1, R2 r2);
impl_query_system!(R0 r0, R1 r1, R2 r2, R3 r3);
impl_query_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4);
impl_query_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4, R5 r5);
impl_query_system!(R0 r0, R1 r1, R2 r2, R3 r3, R4 r4, R5 r5, R6 r6);

/// The marker for a system with resource parameters and two or more
/// world-borrowing query parameters resolved through a shared world cell.
pub struct MultiQuerySystemMarker<R, Q>(PhantomData<fn() -> (R, Q)>);

macro_rules! impl_multi_query_bare {
    ($($query:ident $qbind:ident),+) => {
        impl<Func, $($query,)+> IntoSystem<MultiQuerySystemMarker<(), ($($query,)+)>> for Func
        where
            $($query: MultiQueryParam,)+
            Func: FnMut($($query,)+)
                + for<'world> FnMut($($query::Item<'world>,)+)
                + Send
                + 'static,
        {
            #[allow(non_snake_case)]
            fn into_runner(mut self) -> impl FnMut(&mut DynWorld) + Send + 'static {
                move |world: &mut DynWorld| {
                    let cell = RefCell::new(world);
                    $(let $qbind = $query::build_lazy(&cell);)+
                    self($($qbind,)+);
                }
            }
        }
    };
}

macro_rules! impl_multi_query_resourced {
    (($($resource:ident $rbind:ident),+), ($($query:ident $qbind:ident),+)) => {
        impl<Func, $($resource,)+ $($query,)+>
            IntoSystem<MultiQuerySystemMarker<($($resource,)+), ($($query,)+)>> for Func
        where
            $($resource: ResourceParam,)+
            $($query: MultiQueryParam,)+
            Func: FnMut($($resource,)+ $($query,)+)
                + for<'world> FnMut($($resource::Item<'world>,)+ $($query::Item<'world>,)+)
                + Send
                + 'static,
        {
            #[allow(non_snake_case)]
            fn into_runner(mut self) -> impl FnMut(&mut DynWorld) + Send + 'static {
                move |world: &mut DynWorld| {
                    world.resources_scope::<($($resource::Resource,)+), _>(|world, bundle| {
                        let ($($rbind,)+) = bundle;
                        let cell = RefCell::new(world);
                        $(let $qbind = $query::build_lazy(&cell);)+
                        self($($resource::build($rbind),)+ $($qbind,)+);
                    });
                }
            }
        }
    };
}

impl_multi_query_bare!(Q0 q0, Q1 q1);
impl_multi_query_bare!(Q0 q0, Q1 q1, Q2 q2);
impl_multi_query_bare!(Q0 q0, Q1 q1, Q2 q2, Q3 q3);

impl_multi_query_resourced!((R0 r0), (Q0 q0, Q1 q1));
impl_multi_query_resourced!((R0 r0), (Q0 q0, Q1 q1, Q2 q2));
impl_multi_query_resourced!((R0 r0, R1 r1), (Q0 q0, Q1 q1));
impl_multi_query_resourced!((R0 r0, R1 r1), (Q0 q0, Q1 q1, Q2 q2));
impl_multi_query_resourced!((R0 r0, R1 r1, R2 r2), (Q0 q0, Q1 q1));
impl_multi_query_resourced!((R0 r0, R1 r1, R2 r2), (Q0 q0, Q1 q1, Q2 q2));

#[cfg(test)]
mod tests {
    use super::*;
    use crate::Schedule;
    use crate::dynamic::DynWorld;

    #[derive(Default, Clone, Debug, PartialEq)]
    struct Position {
        x: f32,
        y: f32,
    }

    #[derive(Default, Clone, Debug, PartialEq)]
    struct Velocity {
        x: f32,
        y: f32,
    }

    #[derive(Default, Clone, Debug, PartialEq)]
    struct Health {
        value: f32,
    }

    struct DeltaTime(f32);
    struct Score(u32);
    struct Frozen;

    fn run<Marker>(world: &mut DynWorld, system: impl IntoSystem<Marker>) {
        let mut runner = system.into_runner();
        runner(world);
    }

    #[test]
    fn single_resource_param() {
        let mut world = DynWorld::new();
        world.insert_resource(Score(0));
        run(&mut world, |mut score: ResMut<Score>| score.0 += 5);
        assert_eq!(world.resource::<Score>().unwrap().0, 5);
    }

    #[test]
    fn multiple_resource_params() {
        let mut world = DynWorld::new();
        world.insert_resource(DeltaTime(2.0));
        world.insert_resource(Score(1));
        run(
            &mut world,
            |delta: Res<DeltaTime>, mut score: ResMut<Score>| {
                score.0 += delta.0 as u32;
            },
        );
        assert_eq!(world.resource::<Score>().unwrap().0, 3);
    }

    #[test]
    fn query_only_param() {
        let mut world = DynWorld::new();
        world.spawn((Position { x: 1.0, y: 2.0 },));
        run(&mut world, |query: Query<&mut Position>| {
            query.for_each(|_entity, position| position.x += 10.0);
        });
        let position = world.query_ref::<&Position>().single().unwrap().1.clone();
        assert_eq!(position, Position { x: 11.0, y: 2.0 });
    }

    #[test]
    fn resources_and_query_together() {
        let mut world = DynWorld::new();
        world.insert_resource(DeltaTime(0.5));
        world.insert_resource(Score(0));
        world.spawn((
            Position { x: 0.0, y: 0.0 },
            Velocity { x: 2.0, y: 4.0 },
            Health { value: 100.0 },
        ));
        world.spawn((Position { x: 5.0, y: 5.0 }, Velocity { x: 1.0, y: 1.0 }));

        run(
            &mut world,
            |delta: Res<DeltaTime>,
             mut score: ResMut<Score>,
             query: Query<(&mut Position, &Velocity, Option<&mut Health>)>| {
                query.for_each(|_entity, (position, velocity, health)| {
                    position.x += velocity.x * delta.0;
                    position.y += velocity.y * delta.0;
                    if let Some(health) = health {
                        health.value *= 0.9;
                    }
                });
                score.0 += 1;
            },
        );

        assert_eq!(world.resource::<Score>().unwrap().0, 1);
        let mut positions: Vec<(f32, f32)> = world
            .query_ref::<&Position>()
            .iter()
            .map(|(_entity, position)| (position.x, position.y))
            .collect();
        positions.sort_by(|a, b| a.0.partial_cmp(&b.0).unwrap());
        assert_eq!(positions, vec![(1.0, 2.0), (5.5, 5.5)]);
    }

    #[test]
    fn with_filter_narrows_match() {
        let mut world = DynWorld::new();
        let frozen = world.spawn((Position { x: 0.0, y: 0.0 },));
        world.add_tag_type::<Frozen>(frozen);
        world.spawn((Position { x: 0.0, y: 0.0 },));

        run(&mut world, |query: Query<&mut Position, With<Health>>| {
            query.for_each(|_entity, position| position.x = 1.0);
        });
        assert!(
            world
                .query_ref::<&Position>()
                .iter()
                .all(|(_entity, position)| position.x == 0.0)
        );

        run(
            &mut world,
            |query: Query<&mut Position, WithoutTag<Frozen>>| {
                query.for_each(|_entity, position| position.x = 2.0);
            },
        );
        let moved = world
            .query_ref::<&Position>()
            .iter()
            .filter(|(_entity, position)| position.x == 2.0)
            .count();
        assert_eq!(moved, 1);
    }

    #[test]
    fn changed_filter_visits_only_mutated() {
        let mut world = DynWorld::new();
        let entity = world.spawn((Position { x: 0.0, y: 0.0 },));
        world.spawn((Position { x: 0.0, y: 0.0 },));
        world.step();
        world.get_mut::<Position>(entity).unwrap().x = 1.0;

        let mut visited = 0;
        run(&mut world, |query: Query<&Position, Changed<Position>>| {
            query.for_each(|_entity, _position| {});
        });
        world
            .query_ref::<&Position>()
            .changed::<Position>()
            .iter()
            .for_each(|_| visited += 1);
        assert_eq!(visited, 1);
    }

    #[test]
    fn param_set_lends_conflicting_queries() {
        let mut world = DynWorld::new();
        world.spawn((Position { x: 1.0, y: 1.0 }, Velocity { x: 3.0, y: 3.0 }));

        run(
            &mut world,
            |mut set: ParamSet<(Query<&mut Position>, Query<&Velocity>)>| {
                let mut velocity = (0.0, 0.0);
                set.p1()
                    .for_each(|_entity, value| velocity = (value.x, value.y));
                set.p0().for_each(|_entity, position| {
                    position.x += velocity.0;
                    position.y += velocity.1;
                });
            },
        );

        let position = world.query_ref::<&Position>().single().unwrap().1.clone();
        assert_eq!(position, Position { x: 4.0, y: 4.0 });
    }

    #[test]
    fn two_direct_queries_disjoint_components() {
        let mut world = DynWorld::new();
        world.spawn((Position { x: 1.0, y: 1.0 }, Velocity { x: 3.0, y: 4.0 }));

        run(
            &mut world,
            |positions: Query<&mut Position>, velocities: Query<&Velocity>| {
                let mut sample = (0.0, 0.0);
                velocities.for_each(|_entity, velocity| sample = (velocity.x, velocity.y));
                positions.for_each(|_entity, position| {
                    position.x += sample.0;
                    position.y += sample.1;
                });
            },
        );

        let position = world.query_ref::<&Position>().single().unwrap().1.clone();
        assert_eq!(position, Position { x: 4.0, y: 5.0 });
    }

    #[test]
    fn two_direct_queries_same_component_run_sequentially() {
        let mut world = DynWorld::new();
        world.spawn((Position { x: 0.0, y: 0.0 },));

        run(
            &mut world,
            |first: Query<&mut Position>, second: Query<&mut Position>| {
                first.for_each(|_entity, position| position.x += 1.0);
                second.for_each(|_entity, position| position.x += 10.0);
            },
        );

        assert_eq!(world.query_ref::<&Position>().single().unwrap().1.x, 11.0);
    }

    #[test]
    fn resource_with_two_direct_queries() {
        let mut world = DynWorld::new();
        world.insert_resource(Score(0));
        world.spawn((Position { x: 0.0, y: 0.0 }, Velocity { x: 2.0, y: 0.0 }));

        run(
            &mut world,
            |mut score: ResMut<Score>,
             positions: Query<&mut Position>,
             velocities: Query<&Velocity>| {
                let mut velocity_x = 0.0;
                velocities.for_each(|_entity, velocity| velocity_x = velocity.x);
                positions.for_each(|_entity, position| position.x += velocity_x);
                score.0 += 1;
            },
        );

        assert_eq!(world.resource::<Score>().unwrap().0, 1);
        assert_eq!(world.query_ref::<&Position>().single().unwrap().1.x, 2.0);
    }

    #[test]
    fn schedule_add_system_runs_param_systems() {
        let mut world = DynWorld::new();
        world.insert_resource(Score(0));
        world.spawn((Position { x: 0.0, y: 0.0 }, Velocity { x: 1.0, y: 0.0 }));

        fn movement(query: Query<(&mut Position, &Velocity)>) {
            query.for_each(|_entity, (position, velocity)| position.x += velocity.x);
        }
        fn scoring(mut score: ResMut<Score>) {
            score.0 += 1;
        }

        let mut schedule = Schedule::new();
        schedule.add_system("movement", movement);
        schedule.add_system("scoring", scoring);
        schedule.run(&mut world);
        schedule.run(&mut world);

        assert_eq!(world.resource::<Score>().unwrap().0, 2);
        let position = world.query_ref::<&Position>().single().unwrap().1.clone();
        assert_eq!(position, Position { x: 2.0, y: 0.0 });
    }

    #[test]
    fn added_filter_visits_only_new() {
        let mut world = DynWorld::new();
        world.spawn((Position { x: 0.0, y: 0.0 },));
        world.step();
        world.spawn((Position { x: 9.0, y: 9.0 },));

        run(
            &mut world,
            |query: Query<&mut Position, Added<Position>>| {
                query.for_each(|_entity, position| position.y = 100.0);
            },
        );
        let marked = world
            .query_ref::<&Position>()
            .iter()
            .filter(|(_entity, position)| position.y == 100.0)
            .map(|(_entity, position)| position.x)
            .collect::<Vec<_>>();
        assert_eq!(marked, vec![9.0]);
    }

    #[test]
    fn tuple_filter_combines_constraints() {
        let mut world = DynWorld::new();
        world.spawn((Position { x: 0.0, y: 0.0 }, Health { value: 1.0 }));
        world.spawn((
            Position { x: 0.0, y: 0.0 },
            Health { value: 1.0 },
            Velocity { x: 0.0, y: 0.0 },
        ));

        run(
            &mut world,
            |query: Query<&mut Position, (With<Health>, Without<Velocity>)>| {
                query.for_each(|_entity, position| position.x = 1.0);
            },
        );
        let moved = world
            .query_ref::<&Position>()
            .iter()
            .filter(|(_entity, position)| position.x == 1.0)
            .count();
        assert_eq!(moved, 1);
    }

    #[test]
    fn par_for_each_runs_over_query() {
        let mut world = DynWorld::new();
        for index in 0..64 {
            world.spawn((
                Position {
                    x: index as f32,
                    y: 0.0,
                },
                Velocity { x: 1.0, y: 0.0 },
            ));
        }
        run(&mut world, |query: Query<(&mut Position, &Velocity)>| {
            query.par_for_each(|_entity, (position, velocity)| position.x += velocity.x);
        });
        let total: f32 = world
            .query_ref::<&Position>()
            .iter()
            .map(|(_entity, position)| position.x)
            .sum();
        assert_eq!(total, (0..64).map(|index| index as f32 + 1.0).sum());
    }

    #[test]
    #[should_panic(expected = "DeltaTime")]
    fn missing_resource_panics() {
        let mut world = DynWorld::new();
        run(&mut world, |_delta: Res<DeltaTime>| {});
    }
}