use std::future::Future;

/// Handler trait for asynchronous event callbacks.
///
/// This trait is automatically implemented for any closure matching
/// `Fn(E) -> Future<Output = ()> + Send + Sync + 'static`.
///
/// By using `Fn(E) -> <Self as AsyncHandler<E>>::Fut` as a supertrait,
/// Rust propagates the event type `E` directly into the closure's parameter,
/// enabling seamless turbofish syntax with clean field access:
///
/// ```rust,no_run
/// # use event_bus::EventBus;
/// # #[derive(Clone)] struct MessageUpdatedEvent { id: u64 }
/// # let bus = EventBus::new();
/// bus.on_async::<MessageUpdatedEvent>(|event| async move {
///     println!("Updated: {:?}", event.id);
/// });
/// ```
pub trait AsyncHandler<E>: Fn(E) -> <Self as AsyncHandler<E>>::Fut + Send + Sync + 'static {
    type Fut: Future<Output = ()> + Send + 'static;
}

impl<E, F, Fut> AsyncHandler<E> for F
where
    F: Fn(E) -> Fut + Send + Sync + 'static,
    Fut: Future<Output = ()> + Send + 'static,
{
    type Fut = Fut;
}

/// Handler trait for asynchronous event callbacks with an injected context.
///
/// Automatically implemented for closures matching
/// `Fn(C, E) -> Future<Output = ()> + Send + Sync + 'static`.
pub trait AsyncHandlerWith<E, C>: Fn(C, E) -> <Self as AsyncHandlerWith<E, C>>::Fut + Send + Sync + 'static {
    type Fut: Future<Output = ()> + Send + 'static;
}

impl<E, C, F, Fut> AsyncHandlerWith<E, C> for F
where
    C: Clone + Send + Sync + 'static,
    F: Fn(C, E) -> Fut + Send + Sync + 'static,
    Fut: Future<Output = ()> + Send + 'static,
{
    type Fut = Fut;
}