use std::{
    future::Future,
    sync::Arc,
    task::{Context, Poll, Wake},
};

struct ThreadWaker {
    thread: std::thread::Thread,
}

impl Wake for ThreadWaker {
    fn wake(self: Arc<Self>) {
        self.thread.unpark();
    }

    fn wake_by_ref(self: &Arc<Self>) {
        self.thread.unpark();
    }
}

pub(super) fn block_on<F>(fut: F) -> F::Output
where
    F: Future,
{
    let thread_waker = Arc::new(ThreadWaker {
        thread: std::thread::current(),
    })
    .into();

    let mut ctx = Context::from_waker(&thread_waker);

    let mut fut = std::pin::pin!(fut);

    loop {
        if let Poll::Ready(out) = fut.as_mut().poll(&mut ctx) {
            return out;
        }

        // doesn't race - unpark followed by park will result in park returning immediately
        std::thread::park();
    }
}