keep style info

gpx-rs/engine/src/engine/command/edit/new_track.rs

@@ -12,11 +12,22 @@ impl Apply for NewTrack {
 
 impl Editor for NewTrack {
     fn file(&mut self, file: &mut File) -> Edit {
-        file.trk.push(Track::default());
+        let mut track = Track::default();
+        track.info.color = common(file, |t| &t.info.color);
+        track.info.opacity = common(file, |t| &t.info.opacity);
+        track.info.width = common(file, |t| &t.info.width);
+        file.trk.push(track);
         Edit::Changed
     }
 }
 
+/// Returns the value of a style attribute if all existing tracks agree on it.
+fn common<T: Clone + PartialEq>(file: &File, get: impl Fn(&Track) -> &Option<T>) -> Option<T> {
+    let mut tracks = file.trk.iter();
+    let first = get(tracks.next()?);
+    tracks.all(|t| get(t) == first).then(|| first.clone())?
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{New, engine::command::fixture::Fixture};
@@ -33,4 +44,22 @@ mod tests {
         assert_eq!(file.trk.len(), 2);
         assert_ne!(file.trk[0].id, file.trk[1].id);
     }
+
+    #[test]
+    fn test_new_track_inherits_agreeing_style_only() {
+        let mut fx = Fixture::default();
+        New { name: "file" }.apply(&mut fx.state()).unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        let file = std::rc::Rc::make_mut(fx.files.values_mut().next().unwrap());
+        for (i, trk) in file.trk.iter_mut().enumerate() {
+            trk.info.color = Some("ff0000".into());
+            trk.info.opacity = Some(0.5 + i as f64 * 0.1);
+        }
+        NewTrack.apply(&mut fx.state()).unwrap();
+        let info = &fx.files.values().next().unwrap().trk[2].info;
+        assert_eq!(info.color.as_deref(), Some("ff0000"));
+        assert_eq!(info.opacity, None);
+        assert_eq!(info.width, None);
+    }
 }