improve mycelium argument

Listings/mycelium_find_best_route.rs

@@ -0,0 +1,29 @@
+fn find_best_route<'a>(&self, routes: &'a RouteList)
+    -> Option<&'a RouteEntry>
+{
+    let source_table = self.source_table.read().unwrap();
+    let current = routes.selected();
+    let best = routes
+        .iter()
+        .filter(|re| !re.metric().is_infinite()
+                   && source_table.route_feasible(re))
+        .min_by_key(|re|
+            re.metric() + Metric::from(re.neighbour().link_cost()));
+
+    if let (Some(best), Some(current)) = (best, current) {
+        // Only switch if the metric is significantly better
+        // OR if the route is directly connected (metric 0).
+        if (best.source() != current.source()
+         || best.neighbour() != current.neighbour())
+        && !(best.metric()
+               + Metric::from(best.neighbour().link_cost())
+             < current.metric()
+               + Metric::from(current.neighbour().link_cost())
+               - SIGNIFICANT_METRIC_IMPROVEMENT
+            || best.metric().is_direct())
+        {
+            return Some(current); // keep existing route
+        }
+    }
+    best
+}