use serde::{Deserialize, Serialize};

/// A label in a specific language (BCP-47 tag, e.g. "sv", "en").
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct LocalizedLabel {
    pub lang: String,
    pub label: String,
}

/// Pick the best label for `lang`, falling back to `fallback`, then the first.
pub fn pick_label<'a>(labels: &'a [LocalizedLabel], lang: &str, fallback: &str) -> Option<&'a str> {
    labels
        .iter()
        .find(|l| l.lang == lang)
        .or_else(|| labels.iter().find(|l| l.lang == fallback))
        .or_else(|| labels.first())
        .map(|l| l.label.as_str())
}

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

    fn sample() -> Vec<LocalizedLabel> {
        vec![
            LocalizedLabel {
                lang: "sv".into(),
                label: "trä".into(),
            },
            LocalizedLabel {
                lang: "en".into(),
                label: "wood".into(),
            },
        ]
    }

    #[test]
    fn prefers_requested_language() {
        assert_eq!(pick_label(&sample(), "sv", "en"), Some("trä"));
    }

    #[test]
    fn falls_back_then_first() {
        assert_eq!(pick_label(&sample(), "de", "en"), Some("wood"));
        assert_eq!(pick_label(&sample(), "de", "fr"), Some("trä"));
        assert_eq!(pick_label(&[], "sv", "en"), None);
    }
}