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#![no_std]

#![feature(arbitrary_self_types)]

extern crate pin_api;
extern crate futures_core;
extern crate futures_executor;

macro_rules! if_std {
    ($($i:item)*) => ($(
        #[cfg(feature = "std")]
        $i
    )*)
}

use pin_api::{PinMut, Unpin};
use futures_core::{Future, Stream, Poll, task};

if_std! {
    mod executor;
    mod unsafe_pin;

    use pin_api::PinBox;

    pub use executor::{StableExecutor, block_on_stable};
    use unsafe_pin::UnsafePin;
}

pub trait StableFuture {
    type Item;
    type Error;

    fn poll(self: PinMut<Self>, ctx: &mut task::Context) -> Poll<Self::Item, Self::Error>;

    #[cfg(feature = "std")]
    fn pin<'a>(self) -> PinBox<Future<Item = Self::Item, Error = Self::Error> + Send + 'a>
        where Self: Send + Sized + 'a
    {
        PinBox::new(unsafe { UnsafePin::new(self) })
    }

    #[cfg(feature = "std")]
    fn pin_local<'a>(self) -> PinBox<Future<Item = Self::Item, Error = Self::Error> + 'a>
        where Self: Sized + 'a
    {
        PinBox::new(unsafe { UnsafePin::new(self) })
    }
}

impl<F: Future + Unpin> StableFuture for F {
    type Item = F::Item;
    type Error = F::Error;

    fn poll(mut self: PinMut<Self>, ctx: &mut task::Context) -> Poll<Self::Item, Self::Error> {
        F::poll(&mut *self, ctx)
    }
}

pub trait StableStream {
    type Item;
    type Error;

    fn poll_next(self: PinMut<Self>, ctx: &mut task::Context) -> Poll<Option<Self::Item>, Self::Error>;

    #[cfg(feature = "std")]
    fn pin<'a>(self) -> PinBox<Stream<Item = Self::Item, Error = Self::Error> + Send + 'a>
        where Self: Send + Sized + 'a
    {
        PinBox::new(unsafe { UnsafePin::new(self) })
    }

    #[cfg(feature = "std")]
    fn pin_local<'a>(self) -> PinBox<Stream<Item = Self::Item, Error = Self::Error> + 'a>
        where Self: Sized + 'a
    {
        PinBox::new(unsafe { UnsafePin::new(self) })
    }
}

impl<S: Stream + Unpin> StableStream for S {
    type Item = S::Item;
    type Error = S::Error;

    fn poll_next(mut self: PinMut<Self>, ctx: &mut task::Context) -> Poll<Option<Self::Item>, Self::Error> {
        S::poll_next(&mut *self, ctx)
    }
}