pijul 0.12.2

A patch-based distributed version control system, easy to use and fast. Command-line interface.
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use futures::{Async, Future, IntoFuture, Poll, Stream};
use std::mem;

/// A future used to collect all the results of a stream into one generic type.
///
/// This future is returned by the `Stream::fold` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct FoldWhile<S, F, G, Fut, Gut, T>
where
    Fut: IntoFuture,
    Gut: IntoFuture,
{
    stream: S,
    f: F,
    state: State<T, Fut::Future, Gut::Future>,
    g: G,
}

#[derive(Debug)]
enum State<T, F, G>
where
    F: Future,
    G: Future,
{
    /// Placeholder state when doing work
    Empty,

    /// Ready to process the next stream item; current accumulator is the `T`
    Ready(T),

    /// Working on a future the process the previous stream item
    Processing(F),

    /// Checking whether we can continue.
    Checking(G),
}

pub fn new<S, F, G, Fut, Gut, T>(s: S, t: T, f: F, g: G) -> FoldWhile<S, F, G, Fut, Gut, T>
where
    S: Stream,
    F: FnMut(T, S::Item) -> Fut,
    G: FnMut(T) -> Gut,
    Fut: IntoFuture<Item = T>,
    Gut: IntoFuture<Item = (bool, T)>,
    S::Error: From<Fut::Error> + From<Gut::Error>,
{
    FoldWhile {
        stream: s,
        f: f,
        state: State::Ready(t),
        g: g,
    }
}

impl<S, F, G, Fut, Gut, T> Future for FoldWhile<S, F, G, Fut, Gut, T>
where
    S: Stream,
    F: FnMut(T, S::Item) -> Fut,
    G: FnMut(T) -> Gut,
    Fut: IntoFuture<Item = T>,
    Gut: IntoFuture<Item = (bool, T)>,
    S::Error: From<Fut::Error> + From<Gut::Error>,
{
    type Item = T;
    type Error = S::Error;

    fn poll(&mut self) -> Poll<T, S::Error> {
        loop {
            match mem::replace(&mut self.state, State::Empty) {
                State::Empty => panic!("cannot poll Fold twice"),
                State::Ready(state) => match self.stream.poll()? {
                    Async::Ready(Some(e)) => {
                        let future = (self.f)(state, e);
                        let future = future.into_future();
                        self.state = State::Processing(future);
                    }
                    Async::Ready(None) => return Ok(Async::Ready(state)),
                    Async::NotReady => {
                        self.state = State::Ready(state);
                        return Ok(Async::NotReady);
                    }
                },
                State::Processing(mut fut) => match fut.poll()? {
                    Async::Ready(state) => {
                        self.state = State::Checking((self.g)(state).into_future())
                    }
                    Async::NotReady => {
                        self.state = State::Processing(fut);
                        return Ok(Async::NotReady);
                    }
                },
                State::Checking(mut gut) => match gut.poll()? {
                    Async::Ready((true, state)) => self.state = State::Ready(state),
                    Async::Ready((false, state)) => return Ok(Async::Ready(state)),
                    Async::NotReady => {
                        self.state = State::Checking(gut);
                        return Ok(Async::NotReady);
                    }
                },
            }
        }
    }
}