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use std::task::{Context, Poll};
use tower_layer::Layer;
use tower_service::Service;

/// Service returned by the [`MapRequest`] combinator.
///
/// [`MapRequest`]: crate::util::ServiceExt::map_request
#[derive(Clone, Debug)]
pub struct MapRequest<S, F> {
    inner: S,
    f: F,
}

impl<S, F> MapRequest<S, F> {
    /// Creates a new [`MapRequest`] service.
    pub fn new(inner: S, f: F) -> Self {
        MapRequest { inner, f }
    }
}

impl<S, F, R1, R2> Service<R1> for MapRequest<S, F>
where
    S: Service<R2>,
    F: FnMut(R1) -> R2,
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = S::Future;

    #[inline]
    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
        self.inner.poll_ready(cx)
    }

    #[inline]
    fn call(&mut self, request: R1) -> S::Future {
        self.inner.call((self.f)(request))
    }
}

/// A [`Layer`] that produces a [`MapRequest`] service.
///
/// [`Layer`]: tower_layer::Layer
#[derive(Debug)]
pub struct MapRequestLayer<F> {
    f: F,
}

impl<F> MapRequestLayer<F> {
    /// Creates a new [`MapRequestLayer`].
    pub fn new(f: F) -> Self {
        MapRequestLayer { f }
    }
}

impl<S, F> Layer<S> for MapRequestLayer<F>
where
    F: Clone,
{
    type Service = MapRequest<S, F>;

    fn layer(&self, inner: S) -> Self::Service {
        MapRequest {
            f: self.f.clone(),
            inner,
        }
    }
}