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use std::any::{type_name, Any, TypeId};
use std::fmt::Debug;
use std::marker::PhantomData;
use std::ops::{Deref, DerefMut};
use std::sync::{Arc, Weak};
use crate::lock::{Lock, WriteGuard};
use crate::system::{NoInitParamFlag, Param as SystemParam, System};
use crate::type_name::TypeName;
use crate::World;
/// A type which has a single instance and is shared globally.
pub trait Sole: Any + TypeName
{
fn drop_last(&self) -> bool;
fn as_any_mut(&mut self) -> &mut dyn Any;
fn as_any(&self) -> &dyn Any;
}
impl dyn Sole
{
pub fn downcast_mut<Real: 'static>(&mut self) -> Option<&mut Real>
{
self.as_any_mut().downcast_mut()
}
pub fn downcast_ref<Real: 'static>(&self) -> Option<&Real>
{
self.as_any().downcast_ref()
}
}
impl Debug for dyn Sole
{
fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
{
formatter.debug_struct("Sole").finish_non_exhaustive()
}
}
impl TypeName for Box<dyn Sole>
{
fn type_name(&self) -> &'static str
{
self.as_ref().type_name()
}
}
/// Holds a reference to a globally shared singleton value.
#[derive(Debug)]
pub struct Single<'world, SoleT: Sole>
{
sole: WriteGuard<'world, Box<dyn Sole>>,
sole_weak: Weak<Lock<Box<dyn Sole>>>,
_ph: PhantomData<SoleT>,
}
impl<'world, SoleT> Single<'world, SoleT>
where
SoleT: Sole,
{
/// Returns a struct which holds a weak reference to the [`World`] that `Single`
/// references and that can be used to aquire a new `Single` if the referenced
/// [`World`] is still alive.
#[must_use]
pub fn to_weak_ref(&self) -> SingleWeakRef<SoleT>
{
SingleWeakRef {
sole: self.sole_weak.clone(),
_ph: PhantomData,
}
}
fn new(sole: &'world Arc<Lock<Box<dyn Sole>>>) -> Self
{
Self {
sole: sole.write_nonblock().unwrap_or_else(|_| {
panic!(
"Failed to aquire read-write lock to single component {}",
type_name::<SoleT>()
)
}),
sole_weak: Arc::downgrade(sole),
_ph: PhantomData,
}
}
}
unsafe impl<'world, SoleT> SystemParam<'world> for Single<'world, SoleT>
where
SoleT: Sole,
{
type Flags = NoInitParamFlag;
type Input = ();
fn initialize<SystemImpl>(
_system: &mut impl System<'world, SystemImpl>,
_input: Self::Input,
)
{
}
fn new<SystemImpl>(
_system: &'world impl System<'world, SystemImpl>,
world: &'world World,
) -> Self
{
let sole = world.data.sole_storage.get::<SoleT>().unwrap_or_else(|| {
panic!("Sole {} was not found in world", type_name::<SoleT>())
});
Self::new(sole)
}
fn is_compatible<Other: SystemParam<'world>>() -> bool
{
let other_comparable = Other::get_comparable();
let Some(comparable) = other_comparable.downcast_ref::<Comparable>() else {
// The other system param is not Single
return true;
};
TypeId::of::<SoleT>() != comparable.sole_type_id
}
fn get_comparable() -> Box<dyn Any>
{
Box::new(Comparable { sole_type_id: TypeId::of::<SoleT>() })
}
}
impl<'world, SoleT> Deref for Single<'world, SoleT>
where
SoleT: Sole,
{
type Target = SoleT;
fn deref(&self) -> &Self::Target
{
self.sole.downcast_ref().unwrap()
}
}
impl<'world, SoleT> DerefMut for Single<'world, SoleT>
where
SoleT: Sole,
{
fn deref_mut(&mut self) -> &mut Self::Target
{
self.sole.downcast_mut().unwrap()
}
}
#[derive(Debug, Clone)]
pub struct SingleWeakRef<SoleT>
where
SoleT: Sole,
{
sole: Weak<Lock<Box<dyn Sole>>>,
_ph: PhantomData<SoleT>,
}
impl<SoleT> SingleWeakRef<SoleT>
where
SoleT: Sole,
{
/// Returns a struct which can be used to retrieve a [`Single`].
///
/// Returns [`None`] if the referenced [`World`] has been dropped.
#[must_use]
pub fn access(&self) -> Option<SingleRef<'_, SoleT>>
{
Some(SingleRef {
sole: self.sole.upgrade()?,
_pd: PhantomData,
})
}
}
/// Intermediate between [`Single`] and [`SingleWeakRef`]. Contains a strong reference to
/// a world which is not allowed direct access to.
#[derive(Debug, Clone)]
pub struct SingleRef<'weak_ref, SoleT>
where
SoleT: Sole,
{
sole: Arc<Lock<Box<dyn Sole>>>,
_pd: PhantomData<&'weak_ref SoleT>,
}
impl<'weak_ref, SoleT> SingleRef<'weak_ref, SoleT>
where
SoleT: Sole,
{
#[must_use]
pub fn to_single(&self) -> Single<'_, SoleT>
{
Single::new(&self.sole)
}
}
struct Comparable
{
sole_type_id: TypeId,
}
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