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use std::fmt::Display;
use futures::{Async, Future};
use void::Void;
use log::LogLevel;

/// Wraps a future which returns `()` and logs its error if it fails. `LogError` itself cannot fail
/// and will always resolve to `()`.
pub struct LogError<F> {
    future: F,
    level: LogLevel,
    description: &'static str,
}

impl<F> LogError<F> {
    pub fn new(
        future: F,
        level: LogLevel,
        description: &'static str,
    ) -> LogError<F> {
        LogError {
            future,
            level,
            description,
        }
    }
}

impl<F> Future for LogError<F>
where
    F: Future<Item=()>,
    F::Error: Display,
{
    type Item = ();
    type Error= Void;

    fn poll(&mut self) -> Result<Async<()>, Void> {
        match self.future.poll() {
            Ok(x) => Ok(x),
            Err(e) => {
                log!(self.level, "{}: {}", self.description, e);
                Ok(Async::Ready(()))
            },
        }
    }
}