Avoid extracting resoure set from backing range set

This is one of fixes for ONOS-4684

Change-Id: I5192df366d16b8aad5f8987abbf539897ca0e51c

@@ -122,7 +122,16 @@ final class EncodableDiscreteResources implements DiscreteResources {
     @Override
     public DiscreteResources add(DiscreteResources other) {
         if (other instanceof EncodableDiscreteResources) {
-            return of(parent, Sets.union(this.values(), other.values()));
+            EncodableDiscreteResources cast = (EncodableDiscreteResources) other;
+            LinkedHashMap<Class<?>, EncodedDiscreteResources> newMap =
+                    Stream.concat(this.map.entrySet().stream(), cast.map.entrySet().stream())
+                            .collect(Collectors.toMap(
+                                    Map.Entry::getKey,
+                                    Map.Entry::getValue,
+                                    EncodedDiscreteResources::add,
+                                    LinkedHashMap::new
+                            ));
+            return new EncodableDiscreteResources(parent, newMap);
         } else if (other instanceof EmptyDiscreteResources) {
             return this;
         }

@@ -93,6 +93,15 @@ final class EncodedDiscreteResources {
         return new EncodedDiscreteResources(newRangeSet, this.codec);
     }
 
+    EncodedDiscreteResources add(EncodedDiscreteResources other) {
+        checkArgument(this.codec.getClass() == other.codec.getClass());
+
+        RangeSet<Integer> newRangeSet = TreeRangeSet.create(this.rangeSet);
+        newRangeSet.addAll(other.rangeSet);
+
+        return new EncodedDiscreteResources(newRangeSet, this.codec);
+    }
+
     boolean isEmpty() {
         return rangeSet.isEmpty();
     }

@@ -62,4 +62,17 @@ public class EncodedDiscreteResourcesTest {
         assertThat(sut.difference(other), is(EncodedDiscreteResources.of(ImmutableSet.of(res2), new VlanIdCodec())));
     }
 
+    @Test
+    public void testAdd() {
+        DiscreteResource res1 = Resources.discrete(DID, PN, VID1).resource();
+        DiscreteResource res2 = Resources.discrete(DID, PN, VID2).resource();
+        DiscreteResource res3 = Resources.discrete(DID, PN, VID3).resource();
+
+        EncodedDiscreteResources sut = EncodedDiscreteResources.of(ImmutableSet.of(res1, res2), new VlanIdCodec());
+        EncodedDiscreteResources other = EncodedDiscreteResources.of(ImmutableSet.of(res1, res3), new VlanIdCodec());
+
+        assertThat(sut.add(other),
+                is(EncodedDiscreteResources.of(ImmutableSet.of(res1, res2, res3), new VlanIdCodec())));
+    }
+
 }