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use futures::Poll;

use actor::Actor;
use fut::chain::Chain;
use fut::{ActorFuture, IntoActorFuture};

/// Future for the `then` combinator, chaining computations on the end of
/// another future regardless of its outcome.
///
/// This is created by the `Future::then` method.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct Then<A, B, F>
where
    A: ActorFuture,
    B: IntoActorFuture<Actor = A::Actor>,
{
    state: Chain<A, B::Future, F>,
}

pub fn new<A, B, F>(future: A, f: F) -> Then<A, B, F>
where
    A: ActorFuture,
    B: IntoActorFuture<Actor = A::Actor>,
{
    Then {
        state: Chain::new(future, f),
    }
}

impl<A, B, F> ActorFuture for Then<A, B, F>
where
    A: ActorFuture,
    B: IntoActorFuture<Actor = A::Actor>,
    F: FnOnce(
        Result<A::Item, A::Error>,
        &mut A::Actor,
        &mut <A::Actor as Actor>::Context,
    ) -> B,
{
    type Item = B::Item;
    type Error = B::Error;
    type Actor = A::Actor;

    fn poll(
        &mut self, act: &mut A::Actor, ctx: &mut <A::Actor as Actor>::Context,
    ) -> Poll<B::Item, B::Error> {
        self.state.poll(act, ctx, |a, f, act, ctx| {
            Ok(Err(f(a, act, ctx).into_future()))
        })
    }
}