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use std::future::Future;
use std::task::{Context, Poll};
use tower_service::Service;

/// Returns a new [`ServiceFn`] with the given closure.
pub fn service_fn<T>(f: T) -> ServiceFn<T> {
    ServiceFn { f }
}

/// A [`Service`] implemented by a closure.
#[derive(Copy, Clone, Debug)]
pub struct ServiceFn<T> {
    f: T,
}

impl<T, F, Request, R, E> Service<Request> for ServiceFn<T>
where
    T: FnMut(Request) -> F,
    F: Future<Output = Result<R, E>>,
{
    type Response = R;
    type Error = E;
    type Future = F;

    fn poll_ready(&mut self, _: &mut Context<'_>) -> Poll<Result<(), E>> {
        Ok(()).into()
    }

    fn call(&mut self, req: Request) -> Self::Future {
        (self.f)(req)
    }
}