bevy/crates/bevy_asset/src/handle.rs

use crate::{
    meta::MetaTransform, Asset, AssetId, AssetIndexAllocator, AssetPath, InternalAssetId,
    UntypedAssetId,
};
use bevy_ecs::prelude::*;
use bevy_reflect::{std_traits::ReflectDefault, Reflect, TypePath};
use bevy_utils::get_short_name;
use crossbeam_channel::{Receiver, Sender};
use std::{
    any::TypeId,
    hash::{Hash, Hasher},
    sync::Arc,
};
use thiserror::Error;
use uuid::Uuid;

/// Provides [`Handle`] and [`UntypedHandle`] _for a specific asset type_.
/// This should _only_ be used for one specific asset type.
#[derive(Clone)]
pub struct AssetHandleProvider {
    pub(crate) allocator: Arc<AssetIndexAllocator>,
    pub(crate) drop_sender: Sender<DropEvent>,
    pub(crate) drop_receiver: Receiver<DropEvent>,
    pub(crate) type_id: TypeId,
}

#[derive(Debug)]
pub(crate) struct DropEvent {
    pub(crate) id: InternalAssetId,
    pub(crate) asset_server_managed: bool,
}

impl AssetHandleProvider {
    pub(crate) fn new(type_id: TypeId, allocator: Arc<AssetIndexAllocator>) -> Self {
        let (drop_sender, drop_receiver) = crossbeam_channel::unbounded();
        Self {
            type_id,
            allocator,
            drop_sender,
            drop_receiver,
        }
    }

    /// Reserves a new strong [`UntypedHandle`] (with a new [`UntypedAssetId`]). The stored [`Asset`] [`TypeId`] in the
    /// [`UntypedHandle`] will match the [`Asset`] [`TypeId`] assigned to this [`AssetHandleProvider`].
    pub fn reserve_handle(&self) -> UntypedHandle {
        let index = self.allocator.reserve();
        UntypedHandle::Strong(self.get_handle(InternalAssetId::Index(index), false, None, None))
    }

    pub(crate) fn get_handle(
        &self,
        id: InternalAssetId,
        asset_server_managed: bool,
        path: Option<AssetPath<'static>>,
        meta_transform: Option<MetaTransform>,
    ) -> Arc<StrongHandle> {
        Arc::new(StrongHandle {
            id: id.untyped(self.type_id),
            drop_sender: self.drop_sender.clone(),
            meta_transform,
            path,
            asset_server_managed,
        })
    }

    pub(crate) fn reserve_handle_internal(
        &self,
        asset_server_managed: bool,
        path: Option<AssetPath<'static>>,
        meta_transform: Option<MetaTransform>,
    ) -> Arc<StrongHandle> {
        let index = self.allocator.reserve();
        self.get_handle(
            InternalAssetId::Index(index),
            asset_server_managed,
            path,
            meta_transform,
        )
    }
}

/// The internal "strong" [`Asset`] handle storage for [`Handle::Strong`] and [`UntypedHandle::Strong`]. When this is dropped,
/// the [`Asset`] will be freed. It also stores some asset metadata for easy access from handles.
#[derive(TypePath)]
pub struct StrongHandle {
    pub(crate) id: UntypedAssetId,
    pub(crate) asset_server_managed: bool,
    pub(crate) path: Option<AssetPath<'static>>,
    /// Modifies asset meta. This is stored on the handle because it is:
    /// 1. configuration tied to the lifetime of a specific asset load
    /// 2. configuration that must be repeatable when the asset is hot-reloaded
    pub(crate) meta_transform: Option<MetaTransform>,
    pub(crate) drop_sender: Sender<DropEvent>,
}

impl Drop for StrongHandle {
    fn drop(&mut self) {
        let _ = self.drop_sender.send(DropEvent {
            id: self.id.internal(),
            asset_server_managed: self.asset_server_managed,
        });
    }
}

impl std::fmt::Debug for StrongHandle {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("StrongHandle")
            .field("id", &self.id)
            .field("asset_server_managed", &self.asset_server_managed)
            .field("path", &self.path)
            .field("drop_sender", &self.drop_sender)
            .finish()
    }
}

/// A strong or weak handle to a specific [`Asset`]. If a [`Handle`] is [`Handle::Strong`], the [`Asset`] will be kept
/// alive until the [`Handle`] is dropped. If a [`Handle`] is [`Handle::Weak`], it does not necessarily reference a live [`Asset`],
/// nor will it keep assets alive.
///
/// [`Handle`] can be cloned. If a [`Handle::Strong`] is cloned, the referenced [`Asset`] will not be freed until _all_ instances
/// of the [`Handle`] are dropped.
///
/// [`Handle::Strong`] also provides access to useful [`Asset`] metadata, such as the [`AssetPath`] (if it exists).
#[derive(Component, Reflect)]
#[reflect(Default, Component, Debug, Hash, PartialEq)]
pub enum Handle<A: Asset> {
    /// A "strong" reference to a live (or loading) [`Asset`]. If a [`Handle`] is [`Handle::Strong`], the [`Asset`] will be kept
    /// alive until the [`Handle`] is dropped. Strong handles also provide access to additional asset metadata.
    Strong(Arc<StrongHandle>),
    /// A "weak" reference to an [`Asset`]. If a [`Handle`] is [`Handle::Weak`], it does not necessarily reference a live [`Asset`],
    /// nor will it keep assets alive.
    Weak(AssetId<A>),
}

impl<T: Asset> Clone for Handle<T> {
    fn clone(&self) -> Self {
        match self {
            Handle::Strong(handle) => Handle::Strong(handle.clone()),
            Handle::Weak(id) => Handle::Weak(*id),
        }
    }
}

impl<A: Asset> Handle<A> {
    /// Create a new [`Handle::Weak`] with the given [`u128`] encoding of a [`Uuid`].
    pub const fn weak_from_u128(value: u128) -> Self {
        Handle::Weak(AssetId::Uuid {
            uuid: Uuid::from_u128(value),
        })
    }

    /// Returns the [`AssetId`] of this [`Asset`].
    #[inline]
    pub fn id(&self) -> AssetId<A> {
        match self {
            Handle::Strong(handle) => handle.id.typed_unchecked(),
            Handle::Weak(id) => *id,
        }
    }

    /// Returns the path if this is (1) a strong handle and (2) the asset has a path
    #[inline]
    pub fn path(&self) -> Option<&AssetPath<'static>> {
        match self {
            Handle::Strong(handle) => handle.path.as_ref(),
            Handle::Weak(_) => None,
        }
    }

    /// Returns `true` if this is a weak handle.
    #[inline]
    pub fn is_weak(&self) -> bool {
        matches!(self, Handle::Weak(_))
    }

    /// Returns `true` if this is a strong handle.
    #[inline]
    pub fn is_strong(&self) -> bool {
        matches!(self, Handle::Strong(_))
    }

    /// Creates a [`Handle::Weak`] clone of this [`Handle`], which will not keep the referenced [`Asset`] alive.
    #[inline]
    pub fn clone_weak(&self) -> Self {
        match self {
            Handle::Strong(handle) => Handle::Weak(handle.id.typed_unchecked::<A>()),
            Handle::Weak(id) => Handle::Weak(*id),
        }
    }

    /// Converts this [`Handle`] to an "untyped" / "generic-less" [`UntypedHandle`], which stores the [`Asset`] type information
    /// _inside_ [`UntypedHandle`]. This will return [`UntypedHandle::Strong`] for [`Handle::Strong`] and [`UntypedHandle::Weak`] for
    /// [`Handle::Weak`].
    #[inline]
    pub fn untyped(self) -> UntypedHandle {
        self.into()
    }
}

impl<A: Asset> Default for Handle<A> {
    fn default() -> Self {
        Handle::Weak(AssetId::default())
    }
}

impl<A: Asset> std::fmt::Debug for Handle<A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let name = get_short_name(std::any::type_name::<A>());
        match self {
            Handle::Strong(handle) => {
                write!(
                    f,
                    "StrongHandle<{name}>{{ id: {:?}, path: {:?} }}",
                    handle.id.internal(),
                    handle.path
                )
            }
            Handle::Weak(id) => write!(f, "WeakHandle<{name}>({:?})", id.internal()),
        }
    }
}

impl<A: Asset> Hash for Handle<A> {
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.id().hash(state);
    }
}

impl<A: Asset> PartialOrd for Handle<A> {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl<A: Asset> Ord for Handle<A> {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.id().cmp(&other.id())
    }
}

impl<A: Asset> PartialEq for Handle<A> {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        self.id() == other.id()
    }
}

impl<A: Asset> Eq for Handle<A> {}

impl<A: Asset> From<&Handle<A>> for AssetId<A> {
    #[inline]
    fn from(value: &Handle<A>) -> Self {
        value.id()
    }
}

impl<A: Asset> From<&Handle<A>> for UntypedAssetId {
    #[inline]
    fn from(value: &Handle<A>) -> Self {
        value.id().into()
    }
}

impl<A: Asset> From<&mut Handle<A>> for AssetId<A> {
    #[inline]
    fn from(value: &mut Handle<A>) -> Self {
        value.id()
    }
}

impl<A: Asset> From<&mut Handle<A>> for UntypedAssetId {
    #[inline]
    fn from(value: &mut Handle<A>) -> Self {
        value.id().into()
    }
}

/// An untyped variant of [`Handle`], which internally stores the [`Asset`] type information at runtime
/// as a [`TypeId`] instead of encoding it in the compile-time type. This allows handles across [`Asset`] types
/// to be stored together and compared.
///
/// See [`Handle`] for more information.
#[derive(Clone)]
pub enum UntypedHandle {
    Strong(Arc<StrongHandle>),
    Weak(UntypedAssetId),
}

impl UntypedHandle {
    /// Returns the [`UntypedAssetId`] for the referenced asset.
    #[inline]
    pub fn id(&self) -> UntypedAssetId {
        match self {
            UntypedHandle::Strong(handle) => handle.id,
            UntypedHandle::Weak(id) => *id,
        }
    }

    /// Returns the path if this is (1) a strong handle and (2) the asset has a path
    #[inline]
    pub fn path(&self) -> Option<&AssetPath<'static>> {
        match self {
            UntypedHandle::Strong(handle) => handle.path.as_ref(),
            UntypedHandle::Weak(_) => None,
        }
    }

    /// Creates an [`UntypedHandle::Weak`] clone of this [`UntypedHandle`], which will not keep the referenced [`Asset`] alive.
    #[inline]
    pub fn clone_weak(&self) -> UntypedHandle {
        match self {
            UntypedHandle::Strong(handle) => UntypedHandle::Weak(handle.id),
            UntypedHandle::Weak(id) => UntypedHandle::Weak(*id),
        }
    }

    /// Returns the [`TypeId`] of the referenced [`Asset`].
    #[inline]
    pub fn type_id(&self) -> TypeId {
        match self {
            UntypedHandle::Strong(handle) => handle.id.type_id(),
            UntypedHandle::Weak(id) => id.type_id(),
        }
    }

    /// Converts to a typed Handle. This _will not check if the target Handle type matches_.
    #[inline]
    pub fn typed_unchecked<A: Asset>(self) -> Handle<A> {
        match self {
            UntypedHandle::Strong(handle) => Handle::Strong(handle),
            UntypedHandle::Weak(id) => Handle::Weak(id.typed_unchecked::<A>()),
        }
    }

    /// Converts to a typed Handle. This will check the type when compiled with debug asserts, but it
    ///  _will not check if the target Handle type matches in release builds_. Use this as an optimization
    /// when you want some degree of validation at dev-time, but you are also very certain that the type
    /// actually matches.
    #[inline]
    pub fn typed_debug_checked<A: Asset>(self) -> Handle<A> {
        debug_assert_eq!(
            self.type_id(),
            TypeId::of::<A>(),
            "The target Handle<A>'s TypeId does not match the TypeId of this UntypedHandle"
        );
        match self {
            UntypedHandle::Strong(handle) => Handle::Strong(handle),
            UntypedHandle::Weak(id) => Handle::Weak(id.typed_unchecked::<A>()),
        }
    }

    /// Converts to a typed Handle. This will panic if the internal [`TypeId`] does not match the given asset type `A`
    #[inline]
    pub fn typed<A: Asset>(self) -> Handle<A> {
        let Ok(handle) = self.try_typed() else {
            panic!(
                "The target Handle<{}>'s TypeId does not match the TypeId of this UntypedHandle",
                std::any::type_name::<A>()
            )
        };

        handle
    }

    /// Converts to a typed Handle. This will panic if the internal [`TypeId`] does not match the given asset type `A`
    #[inline]
    pub fn try_typed<A: Asset>(self) -> Result<Handle<A>, UntypedAssetConversionError> {
        Handle::try_from(self)
    }

    /// The "meta transform" for the strong handle. This will only be [`Some`] if the handle is strong and there is a meta transform
    /// associated with it.
    #[inline]
    pub fn meta_transform(&self) -> Option<&MetaTransform> {
        match self {
            UntypedHandle::Strong(handle) => handle.meta_transform.as_ref(),
            UntypedHandle::Weak(_) => None,
        }
    }
}

impl PartialEq for UntypedHandle {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        self.id() == other.id() && self.type_id() == other.type_id()
    }
}

impl Eq for UntypedHandle {}

impl Hash for UntypedHandle {
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.id().hash(state);
    }
}

impl std::fmt::Debug for UntypedHandle {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            UntypedHandle::Strong(handle) => {
                write!(
                    f,
                    "StrongHandle{{ type_id: {:?}, id: {:?}, path: {:?} }}",
                    handle.id.type_id(),
                    handle.id.internal(),
                    handle.path
                )
            }
            UntypedHandle::Weak(id) => write!(
                f,
                "WeakHandle{{ type_id: {:?}, id: {:?} }}",
                id.type_id(),
                id.internal()
            ),
        }
    }
}

impl PartialOrd for UntypedHandle {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        if self.type_id() == other.type_id() {
            self.id().partial_cmp(&other.id())
        } else {
            None
        }
    }
}

impl From<&UntypedHandle> for UntypedAssetId {
    #[inline]
    fn from(value: &UntypedHandle) -> Self {
        value.id()
    }
}

// Cross Operations

impl<A: Asset> PartialEq<UntypedHandle> for Handle<A> {
    #[inline]
    fn eq(&self, other: &UntypedHandle) -> bool {
        TypeId::of::<A>() == other.type_id() && self.id() == other.id()
    }
}

impl<A: Asset> PartialEq<Handle<A>> for UntypedHandle {
    #[inline]
    fn eq(&self, other: &Handle<A>) -> bool {
        other.eq(self)
    }
}

impl<A: Asset> PartialOrd<UntypedHandle> for Handle<A> {
    #[inline]
    fn partial_cmp(&self, other: &UntypedHandle) -> Option<std::cmp::Ordering> {
        if TypeId::of::<A>() != other.type_id() {
            None
        } else {
            self.id().partial_cmp(&other.id())
        }
    }
}

impl<A: Asset> PartialOrd<Handle<A>> for UntypedHandle {
    #[inline]
    fn partial_cmp(&self, other: &Handle<A>) -> Option<std::cmp::Ordering> {
        Some(other.partial_cmp(self)?.reverse())
    }
}

impl<A: Asset> From<Handle<A>> for UntypedHandle {
    fn from(value: Handle<A>) -> Self {
        match value {
            Handle::Strong(handle) => UntypedHandle::Strong(handle),
            Handle::Weak(id) => UntypedHandle::Weak(id.into()),
        }
    }
}

impl<A: Asset> TryFrom<UntypedHandle> for Handle<A> {
    type Error = UntypedAssetConversionError;

    fn try_from(value: UntypedHandle) -> Result<Self, Self::Error> {
        let found = value.type_id();
        let expected = TypeId::of::<A>();

        if found != expected {
            return Err(UntypedAssetConversionError::TypeIdMismatch { expected, found });
        }

        match value {
            UntypedHandle::Strong(handle) => Ok(Handle::Strong(handle)),
            UntypedHandle::Weak(id) => {
                let Ok(id) = id.try_into() else {
                    return Err(UntypedAssetConversionError::TypeIdMismatch { expected, found });
                };
                Ok(Handle::Weak(id))
            }
        }
    }
}

/// Errors preventing the conversion of to/from an [`UntypedHandle`] and a [`Handle`].
#[derive(Error, Debug, PartialEq, Clone)]
#[non_exhaustive]
pub enum UntypedAssetConversionError {
    /// Caused when trying to convert an [`UntypedHandle`] into a [`Handle`] of the wrong type.
    #[error(
        "This UntypedHandle is for {found:?} and cannot be converted into a Handle<{expected:?}>"
    )]
    TypeIdMismatch { expected: TypeId, found: TypeId },
}

#[cfg(test)]
mod tests {
    use super::*;

    type TestAsset = ();

    const UUID_1: Uuid = Uuid::from_u128(123);
    const UUID_2: Uuid = Uuid::from_u128(456);

    /// Simple utility to directly hash a value using a fixed hasher
    fn hash<T: Hash>(data: &T) -> u64 {
        let mut hasher = bevy_utils::AHasher::default();
        data.hash(&mut hasher);
        hasher.finish()
    }

    /// Typed and Untyped `Handles` should be equivalent to each other and themselves
    #[test]
    fn equality() {
        let typed = AssetId::<TestAsset>::Uuid { uuid: UUID_1 };
        let untyped = UntypedAssetId::Uuid {
            type_id: TypeId::of::<TestAsset>(),
            uuid: UUID_1,
        };

        let typed = Handle::Weak(typed);
        let untyped = UntypedHandle::Weak(untyped);

        assert_eq!(
            Ok(typed.clone()),
            Handle::<TestAsset>::try_from(untyped.clone())
        );
        assert_eq!(UntypedHandle::from(typed.clone()), untyped);
        assert_eq!(typed, untyped);
    }

    /// Typed and Untyped `Handles` should be orderable amongst each other and themselves
    #[allow(clippy::cmp_owned)]
    #[test]
    fn ordering() {
        assert!(UUID_1 < UUID_2);

        let typed_1 = AssetId::<TestAsset>::Uuid { uuid: UUID_1 };
        let typed_2 = AssetId::<TestAsset>::Uuid { uuid: UUID_2 };
        let untyped_1 = UntypedAssetId::Uuid {
            type_id: TypeId::of::<TestAsset>(),
            uuid: UUID_1,
        };
        let untyped_2 = UntypedAssetId::Uuid {
            type_id: TypeId::of::<TestAsset>(),
            uuid: UUID_2,
        };

        let typed_1 = Handle::Weak(typed_1);
        let typed_2 = Handle::Weak(typed_2);
        let untyped_1 = UntypedHandle::Weak(untyped_1);
        let untyped_2 = UntypedHandle::Weak(untyped_2);

        assert!(typed_1 < typed_2);
        assert!(untyped_1 < untyped_2);

        assert!(UntypedHandle::from(typed_1.clone()) < untyped_2);
        assert!(untyped_1 < UntypedHandle::from(typed_2.clone()));

        assert!(Handle::<TestAsset>::try_from(untyped_1.clone()).unwrap() < typed_2);
        assert!(typed_1 < Handle::<TestAsset>::try_from(untyped_2.clone()).unwrap());

        assert!(typed_1 < untyped_2);
        assert!(untyped_1 < typed_2);
    }

    /// Typed and Untyped `Handles` should be equivalently hashable to each other and themselves
    #[test]
    fn hashing() {
        let typed = AssetId::<TestAsset>::Uuid { uuid: UUID_1 };
        let untyped = UntypedAssetId::Uuid {
            type_id: TypeId::of::<TestAsset>(),
            uuid: UUID_1,
        };

        let typed = Handle::Weak(typed);
        let untyped = UntypedHandle::Weak(untyped);

        assert_eq!(
            hash(&typed),
            hash(&Handle::<TestAsset>::try_from(untyped.clone()).unwrap())
        );
        assert_eq!(hash(&UntypedHandle::from(typed.clone())), hash(&untyped));
        assert_eq!(hash(&typed), hash(&untyped));
    }

    /// Typed and Untyped `Handles` should be interchangeable
    #[test]
    fn conversion() {
        let typed = AssetId::<TestAsset>::Uuid { uuid: UUID_1 };
        let untyped = UntypedAssetId::Uuid {
            type_id: TypeId::of::<TestAsset>(),
            uuid: UUID_1,
        };

        let typed = Handle::Weak(typed);
        let untyped = UntypedHandle::Weak(untyped);

        assert_eq!(typed, Handle::try_from(untyped.clone()).unwrap());
        assert_eq!(UntypedHandle::from(typed.clone()), untyped);
    }
}