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mod future_ext;

#[cfg(feature = "prometheus")]
pub mod prometheus;

pub use future_ext::{ObservedFuture, ObservedFutureExt};

/// Represents an observer, which reacts to different events happening to the
/// future.
///
/// If any of the functions is used incorrectly, implementation's behaviour
/// could be undefined but must always be safe.
#[allow(unused_variables)]
pub trait Observer<Out: ?Sized> {
    /// Called once before the first future's poll.
    fn on_first_poll(&mut self) {}

    /// Called each time before the future is polled, but *after* `on_first_poll`.
    fn on_poll(&mut self) {}

    /// Called once after the future returns `Poll::Ready`.
    fn on_poll_ready(&mut self, output: &Out) {}

    /// Called once after `on_poll_ready` or before `on_drop`, depending on
    /// whether future was cancelled or not. It isn't called if there was no
    /// call to `on_first_poll`.
    fn on_finish(&mut self, output: Option<&Out>) {}

    /// Called once before the future is dropped, therefore is never called twice
    /// and forbids calls to other trait's functions.
    fn on_drop(&mut self) {}
}

/// Represents the object that can be seen as a status in metrics system.
pub trait AsStatusLabel {
    /// Get status label of this object.
    fn as_status_label(&self) -> String;
}

impl<T, E: AsStatusLabel> AsStatusLabel for Result<T, E> {
    fn as_status_label(&self) -> String {
        match self {
            Ok(_) => "ok".to_owned(),
            Err(err) => err.as_status_label(),
        }
    }
}

impl AsStatusLabel for str {
    fn as_status_label(&self) -> String {
        self.to_string()
    }
}

#[allow(non_snake_case)]
mod macro_impl {
    use super::Observer;

    macro_rules! impl_observer_tuple {
        ($($t:tt)+) => {
            impl<Out: ?Sized, $($t),+> Observer<Out> for ($($t),+,)
            where
                $($t: Observer<Out>),+
            {
                fn on_first_poll(&mut self) {
                    let ($($t),+,) = self;
                    $($t.on_first_poll();)+
                }

                fn on_poll(&mut self) {
                    let ($($t),+,) = self;
                    $($t.on_poll();)+
                }

                fn on_poll_ready(&mut self, output: &Out) {
                    let ($($t),+,) = self;
                    $($t.on_poll_ready(output);)+
                }

                fn on_finish(&mut self, output: Option<&Out>) {
                    let ($($t),+,) = self;
                    $($t.on_finish(output);)+
                }

                fn on_drop(&mut self) {
                    let ($($t),+,) = self;
                    $($t.on_drop();)+
                }
            }
        }
    }

    impl_observer_tuple! { O1 }
    impl_observer_tuple! { O1 O2 }
    impl_observer_tuple! { O1 O2 O3 }
    impl_observer_tuple! { O1 O2 O3 O4 }
    impl_observer_tuple! { O1 O2 O3 O4 O5 }
    impl_observer_tuple! { O1 O2 O3 O4 O5 O6 }
    impl_observer_tuple! { O1 O2 O3 O4 O5 O6 O7 }
    impl_observer_tuple! { O1 O2 O3 O4 O5 O6 O7 O8 }
}