iris/core/src/widget/handle.rs

use std::{
    marker::{PhantomData, Unsize},
    mem::MaybeUninit,
    ops::CoerceUnsized,
    sync::mpsc::Sender,
};

use crate::{
    Ui, Widget,
    util::{RefCounter, SlotId},
};

pub type WidgetId = SlotId;

/// An identifier for a widget that can index a UI or event ctx to get it.
/// This is a strong handle that does not impl Clone, and when it is dropped,
/// a signal is sent to the owning UI to clean up the resources.
///
/// TODO: ergonomic clones when they get put in rust-analyzer & don't cause ICEs?
pub struct WidgetHandle<State, W: ?Sized = dyn Widget<State>> {
    pub(super) id: WidgetId,
    counter: RefCounter,
    send: Sender<WidgetId>,
    ty: *const W,
    state: PhantomData<State>,
}

/// A weak handle to a widget.
/// Will not keep it alive, but can still be used for indexing like WidgetHandle.
pub struct WidgetRef<State, W: ?Sized = dyn Widget<State>> {
    pub(super) id: WidgetId,
    #[allow(unused)]
    ty: *const W,
    state: PhantomData<State>,
}

pub struct WidgetHandles<State, W: ?Sized = dyn Widget<State>> {
    pub h: WidgetHandle<State, W>,
    pub r: WidgetRef<State, W>,
}

impl<State, W: Widget<State> + ?Sized + Unsize<dyn Widget<State>>> WidgetHandle<State, W> {
    pub fn any(self) -> WidgetHandle<State, dyn Widget<State>> {
        self
    }
}

impl<State, W: ?Sized> WidgetHandle<State, W> {
    pub(crate) fn new(id: WidgetId, send: Sender<WidgetId>) -> Self {
        Self {
            id,
            counter: RefCounter::new(),
            send,
            ty: unsafe { MaybeUninit::zeroed().assume_init() },
            state: PhantomData,
        }
    }

    pub fn id(&self) -> WidgetId {
        self.id
    }

    pub fn refs(&self) -> u32 {
        self.counter.refs()
    }

    pub fn weak(&self) -> WidgetRef<State, W> {
        let Self { ty, id, .. } = *self;
        WidgetRef {
            ty,
            id,
            state: PhantomData,
        }
    }

    pub fn handles(self) -> WidgetHandles<State, W> {
        let r = self.weak();
        WidgetHandles { h: self, r }
    }
}

impl<State, W: ?Sized> WidgetRef<State, W> {
    pub fn id(&self) -> WidgetId {
        self.id
    }
}

impl<State, W: ?Sized> Drop for WidgetHandle<State, W> {
    fn drop(&mut self) {
        if self.counter.drop() {
            let _ = self.send.send(self.id);
        }
    }
}

pub trait WidgetIdFn<State, W: ?Sized = dyn Widget<State>>:
    FnOnce(&mut Ui<State>) -> WidgetHandle<State, W>
{
}
impl<State, W: ?Sized, F: FnOnce(&mut Ui<State>) -> WidgetHandle<State, W>> WidgetIdFn<State, W>
    for F
{
}

pub trait IdLike<State> {
    type Widget: Widget<State> + ?Sized + 'static;
    fn id(&self) -> WidgetId;
}

impl<State, W: Widget<State> + ?Sized> IdLike<State> for &WidgetHandle<State, W> {
    type Widget = W;
    fn id(&self) -> WidgetId {
        self.id
    }
}

impl<State, W: Widget<State> + ?Sized> IdLike<State> for WidgetHandle<State, W> {
    type Widget = W;
    fn id(&self) -> WidgetId {
        self.id
    }
}

impl<State, W: Widget<State> + ?Sized> IdLike<State> for WidgetRef<State, W> {
    type Widget = W;
    fn id(&self) -> WidgetId {
        self.id
    }
}

impl<State: 'static> IdLike<State> for WidgetId {
    type Widget = dyn Widget<State>;
    fn id(&self) -> WidgetId {
        *self
    }
}

impl<T: ?Sized + Unsize<U>, U: ?Sized, State> CoerceUnsized<WidgetHandle<State, U>>
    for WidgetHandle<State, T>
{
}
impl<State, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<WidgetRef<State, U>>
    for WidgetRef<State, T>
{
}

impl<State, W: ?Sized> Clone for WidgetRef<State, W> {
    fn clone(&self) -> Self {
        *self
    }
}
impl<State, W: ?Sized> Copy for WidgetRef<State, W> {}
impl<State, W: ?Sized> PartialEq for WidgetRef<State, W> {
    fn eq(&self, other: &Self) -> bool {
        self.id == other.id
    }
}

impl<W> PartialEq for WidgetHandle<W> {
    fn eq(&self, other: &Self) -> bool {
        self.id == other.id
    }
}

impl<W> std::fmt::Debug for WidgetHandle<W> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.id.fmt(f)
    }
}