rustauth-i18n 0.3.2

//! Parse `Accept-Language` per Better Auth i18n (`parseAcceptLanguage`).

/// Parse `Accept-Language` and return base language tags sorted by quality (highest first).
pub fn parse_accept_language(header: Option<&str>) -> Vec<String> {
    let Some(header) = header else {
        return Vec::new();
    };
    let mut entries: Vec<(usize, String, f32)> = Vec::new();
    for part in header.split(',') {
        let part = part.trim();
        if part.is_empty() {
            continue;
        }
        let mut segments = part.split(';');
        let locale_str = segments.next().unwrap_or("").trim();
        let quality_part = segments.next().unwrap_or("q=1").trim();
        let q = quality_part
            .strip_prefix("q=")
            .and_then(|v| v.parse::<f32>().ok())
            .filter(|value| value.is_finite())
            .unwrap_or(1.0);
        let locale = locale_str.trim().to_owned();
        if !locale.is_empty() {
            let index = entries.len();
            entries.push((index, locale, q));
        }
    }
    // Stable ordering: higher `q` first, then header order (matches upstream `Array.sort`).
    entries.sort_by(|a, b| {
        b.2.partial_cmp(&a.2)
            .unwrap_or(std::cmp::Ordering::Equal)
            .then_with(|| a.0.cmp(&b.0))
    });
    entries.into_iter().map(|(_, locale, _)| locale).collect()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn empty_header() {
        assert!(parse_accept_language(None).is_empty());
        assert!(parse_accept_language(Some("")).is_empty());
    }

    #[test]
    fn quality_ordering() {
        let parsed = parse_accept_language(Some("es;q=0.9, fr;q=0.8, en;q=0.7"));
        assert_eq!(parsed, vec!["es", "fr", "en"]);
    }

    #[test]
    fn base_locale_from_region() {
        let parsed = parse_accept_language(Some("fr-CA"));
        assert_eq!(parsed, vec!["fr-CA"]);
    }

    #[test]
    fn preserves_quality_tie_order() {
        let parsed = parse_accept_language(Some("de;q=0.8, fr;q=0.8, en;q=0.7"));
        assert_eq!(parsed, vec!["de", "fr", "en"]);
    }

    #[test]
    fn handles_uppercase_and_spaces() {
        let parsed = parse_accept_language(Some(" FR-ca ; q=0.9 , en ; q=0.8 "));
        assert_eq!(parsed, vec!["FR-ca", "en"]);
    }

    #[test]
    fn defaults_quality_to_one() {
        let parsed = parse_accept_language(Some("de"));
        assert_eq!(parsed, vec!["de"]);
    }

    #[test]
    fn invalid_quality_defaults_to_one() {
        let parsed = parse_accept_language(Some("fr;q=bogus, de;q=0.5"));
        assert_eq!(parsed, vec!["fr", "de"]);
    }
}