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use futures::Poll;

use actor::Actor;
use fut::ActorStream;

/// A stream combinator which will change the error type of a stream from one
/// type to another.
///
/// This is produced by the `ActorStream::map_err` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct StreamMapErr<S, F> {
    stream: S,
    f: F,
}

pub fn new<S, F, U>(s: S, f: F) -> StreamMapErr<S, F>
    where S: ActorStream,
          F: FnMut(S::Error, &mut S::Actor, &mut <S::Actor as Actor>::Context) -> U,
{
    StreamMapErr {
        stream: s,
        f: f,
    }
}

impl<S, F, U> ActorStream for StreamMapErr<S, F>
    where S: ActorStream,
          F: FnMut(S::Error, &mut S::Actor, &mut <S::Actor as Actor>::Context) -> U,
{
    type Item = S::Item;
    type Error = U;
    type Actor = S::Actor;

    fn poll(&mut self,
            act: &mut Self::Actor,
            ctx: &mut <S::Actor as Actor>::Context) -> Poll<Option<S::Item>, U>
    {
        match self.stream.poll(act, ctx) {
            Ok(ok) => Ok(ok),
            Err(e) => Err((self.f)(e, act, ctx)),
        }
    }
}