#![feature(async_await)]

use std::{future::Future, pin::Pin, task::Poll, ptr};
use std::task::{Waker, RawWaker, RawWakerVTable, Context};

// See if we can run a basic `async fn`
pub async fn foo(x: &u32, y: u32) -> u32 {
    let y = &y;
    let z = 9;
    let z = &z;
    let y = async { *y + *z }.await;
    let a = 10;
    let a = &a;
    *x + y + *a
}

async fn add(x: u32, y: u32) -> u32 {
    async { x + y }.await
}

async fn build_aggregate(a: u32, b: u32, c: u32, d: u32) -> u32 {
    let x = (add(a, b).await, add(c, d).await);
    x.0 + x.1
}

enum Never {}
fn never() -> Never {
    panic!()
}

async fn includes_never(crash: bool, x: u32) -> u32 {
    let mut result = async { x * x }.await;
    if !crash {
        return result;
    }
    #[allow(unused)]
    let bad = never();
    result *= async { x + x }.await;
    drop(bad);
    result
}

fn raw_waker_clone(_this: *const ()) -> RawWaker {
    panic!("unimplemented");
}
fn raw_waker_wake(_this: *const ()) {
    panic!("unimplemented");
}
fn raw_waker_wake_by_ref(_this: *const ()) {
    panic!("unimplemented");
}
fn raw_waker_drop(_this: *const ()) {}

static RAW_WAKER: RawWakerVTable = RawWakerVTable::new(
    raw_waker_clone,
    raw_waker_wake,
    raw_waker_wake_by_ref,
    raw_waker_drop,
);

fn main() {
    let x = 5;
    let mut fut = foo(&x, 7);
    let waker = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &RAW_WAKER)) };
    let mut context = Context::from_waker(&waker);
    assert_eq!(unsafe { Pin::new_unchecked(&mut fut) }.poll(&mut context), Poll::Ready(31));

    let mut fut = build_aggregate(1, 2, 3, 4);
    let waker = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &RAW_WAKER)) };
    let mut context = Context::from_waker(&waker);
    assert_eq!(unsafe { Pin::new_unchecked(&mut fut) }.poll(&mut context), Poll::Ready(10));

    let mut fut = includes_never(false, 4);
    let waker = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &RAW_WAKER)) };
    let mut context = Context::from_waker(&waker);
    assert_eq!(unsafe { Pin::new_unchecked(&mut fut) }.poll(&mut context), Poll::Ready(16));
}