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use futures::{Async, Poll};

use actor::Actor;
use fut::ActorFuture;

/// Future for the `map` combinator, changing the type of a future.
///
/// This is created by the `ActorFuture::map` method.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct Map<A, F>
where
    A: ActorFuture,
{
    future: A,
    f: Option<F>,
}

pub fn new<A, F>(future: A, f: F) -> Map<A, F>
where
    A: ActorFuture,
{
    Map { future, f: Some(f) }
}

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

    fn poll(
        &mut self, act: &mut Self::Actor, ctx: &mut <A::Actor as Actor>::Context,
    ) -> Poll<U, A::Error> {
        let e = match self.future.poll(act, ctx) {
            Ok(Async::NotReady) => return Ok(Async::NotReady),
            Ok(Async::Ready(e)) => Ok(e),
            Err(e) => Err(e),
        };
        match e {
            Ok(item) => Ok(Async::Ready(self.f.take().expect("cannot poll Map twice")(
                item, act, ctx,
            ))),
            Err(err) => Err(err),
        }
    }
}