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//! Helpers for error handling.

/// Format an error, including its chain of sources.
///
/// Always use this when displaying an error.
pub fn format(error: impl AsRef<dyn std::error::Error>) -> String {
    fn format_impl(error: &dyn std::error::Error) -> String {
        let mut string = error.to_string();
        for source in std::iter::successors(error.source(), |error| error.source()) {
            string.push_str(" -> ");
            string.push_str(&source.to_string());
        }
        string
    }

    format_impl(error.as_ref())
}

#[test]
fn test_format() {
    let err = anyhow::format_err!("root_cause")
        .context("inner_context")
        .context("outer_context");

    assert_eq!(err.to_string(), "outer_context"); // Oh no, we don't see the root cause!

    // Now we do:
    assert_eq!(format(&err), "outer_context -> inner_context -> root_cause");
}

pub trait ResultExt<T> {
    fn warn_on_err_once(self, msg: impl std::fmt::Display) -> Option<T>;
}

impl<T, E: std::fmt::Display> ResultExt<T> for Result<T, E> {
    /// Log a warning if there is an `Err`, but only log the exact same message once.
    fn warn_on_err_once(self, msg: impl std::fmt::Display) -> Option<T> {
        match self {
            Ok(value) => Some(value),
            Err(err) => {
                re_log::warn_once!("{msg}: {err}");
                None
            }
        }
    }
}