array__ops 1.0.3

use core::{future::Future, pin::Pin, task::{Context, Poll}};

use crate::ops::ArrayMap;

use super::MaybeDone;

pub struct TryRuns<T, U, E, const N: usize>
where
    T: Future<Output = Result<U, E>>
{
    tasks: [MaybeDone<T>; N]
}

impl<T, U, E, const N: usize> TryRuns<T, U, E, N>
where
    T: Future<Output = Result<U, E>>
{
    pub(crate) fn new(tasks: [T; N]) -> Self
    {
        Self {
            tasks: ArrayMap::map(tasks, |task| MaybeDone::Future(task))
        }
    }
}

impl<T, U, E, const N: usize> Future for TryRuns<T, U, E, N>
where
    T: Future<Output = Result<U, E>>
{
    type Output = Result<[U; N], E>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>
    {
        let mut done = true;

        let mut i = 0;
        
        while i < N
        {
            let task = unsafe {
                self.as_mut()
                    .map_unchecked_mut(|join| &mut join.tasks[i])
            };
            let ready = task.poll(cx)
                .is_ready();
            if ready
            {
                let join = unsafe {
                    self.as_mut()
                        .get_unchecked_mut()
                };
                let result = join.tasks[i].take_output();
                if let Some(Err(error)) = result
                {
                    for task in join.tasks.iter_mut()
                    {
                        task.cancel()
                    }
                    return Poll::Ready(Err(error))
                }
            }
            else
            {
                done = false
            }
            i += 1;
        }

        if !done
        {
            return Poll::Pending
        }

        let join = unsafe {
            self.as_mut()
                .get_unchecked_mut()
        };

        let result = join.tasks.try_map_mut(|task| task.take_output().unwrap());

        Poll::Ready(result)
    }
}