feat(domain): id macro + vocabulary/authority/label value types

crates/domain/src/label.rs

@@ -0,0 +1,48 @@
+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);
+    }
+}