use core::time::Duration;

/// Backoff is an [`Iterator`] that returns [`Duration`].

///

/// - `Some(Duration)` indicates the caller should `sleep(Duration)` and retry the request.

/// - `None` indicates the limits have been reached, and the caller should return the current error instead.

pub trait Backoff: Iterator<Item = Duration> + Send + Sync + Unpin {}

impl<T> Backoff for T where T: Iterator<Item = Duration> + Send + Sync + Unpin {}

/// BackoffBuilder is utilized to construct a new backoff.

pub trait BackoffBuilder: Send + Sync + Unpin {

    /// The associated backoff returned by this builder.

    type Backoff: Backoff;

    /// Construct a new backoff using the builder.

    fn build(self) -> Self::Backoff;

}

impl<B: Backoff> BackoffBuilder for B {

    type Backoff = B;

    fn build(self) -> Self::Backoff {

        self

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    use crate::ConstantBuilder;

    use crate::ExponentialBuilder;

    use crate::FibonacciBuilder;

    fn test_fn_builder(b: impl BackoffBuilder) {

        let _ = b.build();

    }

    #[test]

    fn test_backoff_builder() {

        test_fn_builder([Duration::from_secs(1)].into_iter());

        // Just for test if user can keep using &XxxBuilder.

        #[allow(clippy::needless_borrows_for_generic_args)]

        {

            test_fn_builder(&ConstantBuilder::default());

            test_fn_builder(&FibonacciBuilder::default());

            test_fn_builder(&ExponentialBuilder::default());

        }

    }

}