#[cfg(any(feature = "tree-error", not(feature = "auto-chain-error")))]
mod _impl {
    use crate::{Error, Exn};
    use std::fmt::Formatter;

    /// Utilities
    impl Error {
        /// Return the error that is most likely the root cause, based on heuristics.
        /// Note that if there is nothing but this error, i.e. no source or children, this error is returned.
        pub fn probable_cause(&self) -> &(dyn std::error::Error + 'static) {
            let root = self.inner.frame();
            root.probable_cause().unwrap_or(root).error()
        }

        /// Return an iterator over all errors in the tree in breadth-first order, starting with this one.
        pub fn sources(&self) -> impl Iterator<Item = &(dyn std::error::Error + 'static)> + '_ {
            self.inner.frame().iter_frames().map(|f| f.error() as _)
        }
    }

    pub(crate) enum Inner {
        ExnAsError(Box<crate::exn::Frame>),
        Exn(Box<crate::exn::Frame>),
    }

    impl Inner {
        fn frame(&self) -> &crate::exn::Frame {
            match self {
                Inner::ExnAsError(f) | Inner::Exn(f) => f,
            }
        }
    }

    impl Error {
        /// Create a new instance representing the given `error`.
        #[track_caller]
        pub fn from_error(error: impl std::error::Error + Send + Sync + 'static) -> Self {
            Error {
                inner: Inner::ExnAsError(Exn::new(error).into()),
            }
        }
    }

    impl std::fmt::Display for Error {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            match &self.inner {
                Inner::ExnAsError(err) => std::fmt::Display::fmt(err.error(), f),
                Inner::Exn(frame) => std::fmt::Display::fmt(frame, f),
            }
        }
    }

    impl std::fmt::Debug for Error {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            match &self.inner {
                Inner::ExnAsError(err) => std::fmt::Debug::fmt(err.error(), f),
                Inner::Exn(frame) => std::fmt::Debug::fmt(frame, f),
            }
        }
    }

    impl std::error::Error for Error {
        /// Return the first source of an [Exn] error, or the source of a boxed error.
        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
            match &self.inner {
                Inner::ExnAsError(frame) | Inner::Exn(frame) => frame.children().first().map(|f| f.error() as _),
            }
        }
    }

    impl<E> From<Exn<E>> for Error
    where
        E: std::error::Error + Send + Sync + 'static,
    {
        fn from(err: Exn<E>) -> Self {
            Error {
                inner: Inner::Exn(err.into()),
            }
        }
    }
}
#[cfg(any(feature = "tree-error", not(feature = "auto-chain-error")))]
pub(super) use _impl::Inner;

#[cfg(all(feature = "auto-chain-error", not(feature = "tree-error")))]
mod _impl {
    use crate::{Error, Exn};
    use std::fmt::Formatter;

    /// Utilities
    impl Error {
        /// Return the error that is most likely the root cause, based on heuristics.
        /// Note that if there is nothing but this error, i.e. no source or children, this error is returned.
        pub fn probable_cause(&self) -> &(dyn std::error::Error + 'static) {
            use std::error::Error;
            self.inner
                .source()
                .unwrap_or(self as &(dyn std::error::Error + 'static))
        }

        /// Return an iterator over all errors in the tree in breadth-first order, starting with this one.
        pub fn sources(&self) -> impl Iterator<Item = &(dyn std::error::Error + 'static)> + '_ {
            std::iter::successors(Some(&self.inner as &(dyn std::error::Error + 'static)), |err| {
                err.source()
            })
        }
    }

    impl Error {
        /// Create a new instance representing the given `error`.
        #[track_caller]
        pub fn from_error(error: impl std::error::Error + Send + Sync + 'static) -> Self {
            Error {
                inner: Exn::new(error).into_chain(),
            }
        }
    }

    impl std::fmt::Display for Error {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            std::fmt::Display::fmt(&self.inner, f)
        }
    }

    impl std::fmt::Debug for Error {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            std::fmt::Debug::fmt(&self.inner, f)
        }
    }

    impl std::error::Error for Error {
        /// Return the first source of an [Exn] error, or the source of a boxed error.
        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
            self.inner.source()
        }
    }

    impl<E> From<Exn<E>> for Error
    where
        E: std::error::Error + Send + Sync + 'static,
    {
        fn from(err: Exn<E>) -> Self {
            Error {
                inner: err.into_chain(),
            }
        }
    }
}