//! Middleware which instruments a service with a span entered when that service
//! is called.
use crate::GetSpan;
use std::future::Future;
use std::marker::PhantomData;
use std::pin::Pin;
use std::task::{Context, Poll};

#[derive(Debug)]
pub struct Service<S> {
    inner: S,
    span: tracing::Span,
}

#[cfg(feature = "tower-layer")]
#[cfg_attr(docsrs, doc(cfg(feature = "tower-layer")))]
pub use self::layer::*;

#[cfg(feature = "tower-util")]
#[cfg_attr(docsrs, doc(cfg(feature = "tower-util")))]
pub use self::make::MakeService;

#[cfg(feature = "tower-layer")]
#[cfg_attr(docsrs, doc(cfg(feature = "tower-layer")))]
mod layer {
    use super::*;

    #[derive(Debug)]
    pub struct Layer<S, R, G = fn(&S) -> tracing::Span>
    where
        G: GetSpan<S>,
        S: tower_service::Service<R>,
    {
        get_span: G,
        _p: PhantomData<fn(S, R)>,
    }

    pub fn layer<S, R, G>(get_span: G) -> Layer<S, R, G>
    where
        G: GetSpan<S>,
        S: tower_service::Service<R>,
    {
        Layer {
            get_span,
            _p: PhantomData,
        }
    }

    // === impl Layer ===

    impl<S, R, G> tower_layer::Layer<S> for Layer<S, R, G>
    where
        G: GetSpan<S>,
        S: tower_service::Service<R>,
    {
        type Service = Service<S>;

        fn layer(&self, inner: S) -> Self::Service {
            let span = self.get_span.span_for(&inner);
            Service { inner, span }
        }
    }

    impl<S, R, G> Clone for Layer<S, R, G>
    where
        G: GetSpan<S> + Clone,
        S: tower_service::Service<R>,
    {
        fn clone(&self) -> Self {
            Self {
                get_span: self.get_span.clone(),
                _p: PhantomData,
            }
        }
    }
}

#[cfg(feature = "tower-layer")]
#[cfg_attr(docsrs, doc(cfg(feature = "tower-layer")))]
pub mod make {
    use super::*;
    use pin_project_lite::pin_project;

    #[derive(Debug)]
    pub struct MakeService<M, T, R, G = fn(&T) -> tracing::Span>
    where
        G: GetSpan<T>,
    {
        get_span: G,
        inner: M,
        _p: PhantomData<fn(T, R)>,
    }

    pin_project! {
        #[derive(Debug)]
        pub struct MakeFuture<F> {
            #[pin]
            inner: F,
            span: Option<tracing::Span>,
        }
    }

    #[derive(Debug)]
    pub struct MakeLayer<T, R, G = fn(&T) -> tracing::Span>
    where
        G: GetSpan<T> + Clone,
    {
        get_span: G,
        _p: PhantomData<fn(T, R)>,
    }

    #[cfg(feature = "tower-layer")]
    #[cfg_attr(docsrs, doc(cfg(feature = "tower-layer")))]
    pub fn layer<T, R, G>(get_span: G) -> MakeLayer<T, R, G>
    where
        G: GetSpan<T> + Clone,
    {
        MakeLayer {
            get_span,
            _p: PhantomData,
        }
    }

    // === impl MakeLayer ===

    #[cfg(feature = "tower-layer")]
    #[cfg_attr(docsrs, doc(cfg(feature = "tower-layer")))]
    impl<M, T, R, G> tower_layer::Layer<M> for MakeLayer<T, R, G>
    where
        M: tower_make::MakeService<T, R>,
        G: GetSpan<T> + Clone,
    {
        type Service = MakeService<M, T, R, G>;

        fn layer(&self, inner: M) -> Self::Service {
            MakeService::new(inner, self.get_span.clone())
        }
    }

    #[cfg(feature = "tower-layer")]
    #[cfg_attr(docsrs, doc(cfg(feature = "tower-layer")))]
    impl<T, R, G> Clone for MakeLayer<T, R, G>
    where
        G: GetSpan<T> + Clone,
    {
        fn clone(&self) -> Self {
            Self {
                get_span: self.get_span.clone(),
                _p: PhantomData,
            }
        }
    }

    // === impl MakeService ===

    impl<M, T, R, G> tower_service::Service<T> for MakeService<M, T, R, G>
    where
        M: tower_make::MakeService<T, R>,
        G: GetSpan<T>,
    {
        type Response = Service<M::Service>;
        type Error = M::MakeError;
        type Future = MakeFuture<M::Future>;

        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            self.inner.poll_ready(cx)
        }

        fn call(&mut self, target: T) -> Self::Future {
            let span = self.get_span.span_for(&target);
            let inner = self.inner.make_service(target);
            MakeFuture {
                span: Some(span),
                inner,
            }
        }
    }

    impl<F, T, E> Future for MakeFuture<F>
    where
        F: Future<Output = Result<T, E>>,
    {
        type Output = Result<Service<T>, E>;

        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            let this = self.project();
            let inner = {
                let _guard = this.span.as_ref().map(tracing::Span::enter);
                futures::ready!(this.inner.poll(cx))
            };

            let span = this.span.take().expect("polled after ready");
            Poll::Ready(inner.map(|svc| Service::new(svc, span)))
        }
    }

    impl<M, T, R, G> MakeService<M, T, R, G>
    where
        G: GetSpan<T>,
    {
        pub fn new(inner: M, get_span: G) -> Self {
            MakeService {
                get_span,
                inner,
                _p: PhantomData,
            }
        }
    }

    impl<M, T, R, G> Clone for MakeService<M, T, R, G>
    where
        M: Clone,
        G: GetSpan<T> + Clone,
    {
        fn clone(&self) -> Self {
            Self::new(self.inner.clone(), self.get_span.clone())
        }
    }
}

// === impl Service ===

impl<S> Service<S> {
    pub fn new(inner: S, span: tracing::Span) -> Self {
        Self { inner, span }
    }
}

impl<S, R> tower_service::Service<R> for Service<S>
where
    S: tower_service::Service<R>,
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = S::Future;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        let _enter = self.span.enter();
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, request: R) -> Self::Future {
        let _enter = self.span.enter();
        self.inner.call(request)
    }
}

impl<S> Clone for Service<S>
where
    S: Clone,
{
    fn clone(&self) -> Self {
        Service {
            span: self.span.clone(),
            inner: self.inner.clone(),
        }
    }
}