artifacts: implement merge()

src/artifacts.rs

@@ -85,9 +85,38 @@ pub enum Artifact {
     Track(Track)
 }
 
-impl Artifact {
+macro_rules! merge_fields {
-    pub fn merge(&mut self, other: &Artifact) {
+    ($this:expr, $that:expr, $field:tt) => {
+        if $this.$field.is_none() {
+            $this.$field = $that.$field;
+        }
+    };
+    ($this:tt, $that:tt, $($fields:tt),+) => {
+        $(
+            merge_fields!($this, $that, $fields);
+        )+
+    }
+}
 
+impl Artifact {
+    pub fn merge(&mut self, other: Artifact) {
+        if *self != other {
+            return;
+        }
+
+        match (self, other) {
+            (Artifact::Track(this_track), Artifact::Track(that_track)) => {
+                merge_fields!(this_track, that_track, album, label, year, artist, bpm);
+                // FIXME: genres
+            },
+            (Artifact::Album(this_album), Artifact::Album(that_album)) => {
+                merge_fields!(this_album, that_album, about, credits, release_date);
+            },
+            (Artifact::Artist(this_artist), Artifact::Artist(that_artist)) => {
+                merge_fields!(this_artist, that_artist, bio, location);
+            },
+            _ => ()
+        }
     }
 }