use crate::Stream;

use core::pin::Pin;

use core::task::{Context, Poll};

/// Stream for the [`iter`](fn@iter) function.

#[derive(Debug)]

#[must_use = "streams do nothing unless polled"]

pub struct Iter<I> {

    iter: I,

    #[cfg(not(feature = "rt"))]

    yield_amt: usize,

}

impl<I> Unpin for Iter<I> {}

/// Converts an `Iterator` into a `Stream` which is always ready

/// to yield the next value.

///

/// Iterators in Rust don't express the ability to block, so this adapter

/// simply always calls `iter.next()` and returns that.

///

/// ```

/// # async fn dox() {

/// use tokio_stream::{self as stream, StreamExt};

///

/// let mut stream = stream::iter(vec![17, 19]);

///

/// assert_eq!(stream.next().await, Some(17));

/// assert_eq!(stream.next().await, Some(19));

/// assert_eq!(stream.next().await, None);

/// # }

/// ```

pub fn iter<I>(i: I) -> Iter<I::IntoIter>

where

    I: IntoIterator,

{

    Iter {

        iter: i.into_iter(),

        #[cfg(not(feature = "rt"))]

        yield_amt: 0,

    }

}

impl<I> Stream for Iter<I>

where

    I: Iterator,

{

    type Item = I::Item;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<I::Item>> {

        #[cfg(feature = "rt")]

        {

            use tokio::task::coop;

            let coop = std::task::ready!(coop::poll_proceed(cx));

            let item = self.iter.next();

            coop.made_progress();

            Poll::Ready(item)

        }

        #[cfg(not(feature = "rt"))]

        {

            if self.yield_amt >= 32 {

                self.yield_amt = 0;

                cx.waker().wake_by_ref();

                Poll::Pending

            } else {

                let item = self.iter.next();

                self.yield_amt += 1;

                Poll::Ready(item)

            }

        }

    }

    fn size_hint(&self) -> (usize, Option<usize>) {

        self.iter.size_hint()

    }

}