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//! Service that limits number of in-flight async requests to 1.
use std::{cell::Cell, future::Future, pin::Pin, task::Context, task::Poll};

use ntex_service::{IntoService, Middleware, Service, ServiceCall, ServiceCtx};

use crate::task::LocalWaker;

/// OneRequest - service factory for service that can limit number of in-flight
/// async requests to 1.
#[derive(Copy, Clone, Default, Debug)]
pub struct OneRequest;

impl<S> Middleware<S> for OneRequest {
    type Service = OneRequestService<S>;

    fn create(&self, service: S) -> Self::Service {
        OneRequestService {
            service,
            ready: Cell::new(true),
            waker: LocalWaker::new(),
        }
    }
}

#[derive(Clone, Debug)]
pub struct OneRequestService<S> {
    waker: LocalWaker,
    service: S,
    ready: Cell<bool>,
}

impl<S> OneRequestService<S> {
    pub fn new<U, R>(service: U) -> Self
    where
        S: Service<R>,
        U: IntoService<S, R>,
    {
        Self {
            service: service.into_service(),
            ready: Cell::new(true),
            waker: LocalWaker::new(),
        }
    }
}

impl<T, R> Service<R> for OneRequestService<T>
where
    T: Service<R>,
{
    type Response = T::Response;
    type Error = T::Error;
    type Future<'f> = OneRequestServiceResponse<'f, T, R> where Self: 'f, R: 'f;

    #[inline]
    fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.waker.register(cx.waker());
        if self.service.poll_ready(cx)?.is_pending() {
            Poll::Pending
        } else if self.ready.get() {
            Poll::Ready(Ok(()))
        } else {
            Poll::Pending
        }
    }

    #[inline]
    fn call<'a>(&'a self, req: R, ctx: ServiceCtx<'a, Self>) -> Self::Future<'a> {
        self.ready.set(false);

        OneRequestServiceResponse {
            fut: ctx.call(&self.service, req),
            service: self,
        }
    }

    ntex_service::forward_poll_shutdown!(service);
}

pin_project_lite::pin_project! {
    #[doc(hidden)]
    pub struct OneRequestServiceResponse<'f, T: Service<R>, R>
    where T: 'f, R: 'f
    {
        #[pin]
        fut: ServiceCall<'f, T, R>,
        service: &'f OneRequestService<T>,
    }
}

impl<'f, T: Service<R>, R> Future for OneRequestServiceResponse<'f, T, R> {
    type Output = Result<T::Response, T::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let result = self.as_mut().project().fut.poll(cx);
        if result.is_ready() {
            self.service.ready.set(true);
            self.service.waker.wake();
        }
        result
    }
}

#[cfg(test)]
mod tests {
    use ntex_service::{apply, fn_factory, Pipeline, Service, ServiceCtx, ServiceFactory};
    use std::{cell::RefCell, task::Poll, time::Duration};

    use super::*;
    use crate::{channel::oneshot, future::lazy, future::BoxFuture};

    struct SleepService(oneshot::Receiver<()>);

    impl Service<()> for SleepService {
        type Response = ();
        type Error = ();
        type Future<'f> = BoxFuture<'f, Result<(), ()>>;

        fn call<'a>(&'a self, _: (), _: ServiceCtx<'a, Self>) -> Self::Future<'a> {
            Box::pin(async move {
                let _ = self.0.recv().await;
                Ok::<_, ()>(())
            })
        }
    }

    #[ntex_macros::rt_test2]
    async fn test_oneshot() {
        let (tx, rx) = oneshot::channel();

        let srv = Pipeline::new(OneRequestService::new(SleepService(rx)));
        assert_eq!(lazy(|cx| srv.poll_ready(cx)).await, Poll::Ready(Ok(())));

        let srv2 = srv.clone();
        ntex::rt::spawn(async move {
            let _ = srv2.call(()).await;
        });
        crate::time::sleep(Duration::from_millis(25)).await;
        assert_eq!(lazy(|cx| srv.poll_ready(cx)).await, Poll::Pending);

        let _ = tx.send(());
        crate::time::sleep(Duration::from_millis(25)).await;
        assert_eq!(lazy(|cx| srv.poll_ready(cx)).await, Poll::Ready(Ok(())));
        assert!(lazy(|cx| srv.poll_shutdown(cx)).await.is_ready());
    }

    #[ntex_macros::rt_test2]
    async fn test_middleware() {
        assert_eq!(format!("{:?}", OneRequest), "OneRequest");

        let (tx, rx) = oneshot::channel();
        let rx = RefCell::new(Some(rx));
        let srv = apply(
            OneRequest,
            fn_factory(move || {
                let rx = rx.borrow_mut().take().unwrap();
                async move { Ok::<_, ()>(SleepService(rx)) }
            }),
        );

        let srv = srv.pipeline(&()).await.unwrap();
        assert_eq!(lazy(|cx| srv.poll_ready(cx)).await, Poll::Ready(Ok(())));

        let srv2 = srv.clone();
        ntex::rt::spawn(async move {
            let _ = srv2.call(()).await;
        });
        crate::time::sleep(Duration::from_millis(25)).await;
        assert_eq!(lazy(|cx| srv.poll_ready(cx)).await, Poll::Pending);

        let _ = tx.send(());
        crate::time::sleep(Duration::from_millis(25)).await;
        assert_eq!(lazy(|cx| srv.poll_ready(cx)).await, Poll::Ready(Ok(())));
    }
}