Avoid extracting resoure set from backing range set

This is one of fixes for ONOS-4684

Change-Id: I93cd95317b985f98fd6e72a4f96c7f7d6857f279

@@ -30,6 +30,7 @@ import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * A set of discrete resources that can be encoded as integers.
@@ -88,7 +89,16 @@ final class EncodableDiscreteResources implements DiscreteResources {
     @Override
     public DiscreteResources difference(DiscreteResources other) {
         if (other instanceof EncodableDiscreteResources) {
-            return of(parent, Sets.difference(this.values(), other.values()));
+            EncodableDiscreteResources cast = (EncodableDiscreteResources) other;
+            Map<Class<?>, EncodedDiscreteResources> newMap =
+                    Stream.concat(this.map.entrySet().stream(), cast.map.entrySet().stream())
+                            .filter(entry -> this.map.containsKey(entry.getKey()))
+                            .collect(Collectors.toMap(
+                                    Map.Entry::getKey,
+                                    Map.Entry::getValue,
+                                    EncodedDiscreteResources::difference,
+                                    LinkedHashMap::new));
+            return new EncodableDiscreteResources(parent, newMap);
         } else if (other instanceof EmptyDiscreteResources) {
             return this;
         }

@@ -32,6 +32,8 @@ import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 
+import static com.google.common.base.Preconditions.checkArgument;
+
 /**
  * Represents discrete resources encoded by a codec.
  */
@@ -82,6 +84,15 @@ final class EncodedDiscreteResources {
                 .orElse(false);
     }
 
+    EncodedDiscreteResources difference(EncodedDiscreteResources other) {
+        checkArgument(this.codec.getClass() == other.codec.getClass());
+
+        RangeSet<Integer> newRangeSet = TreeRangeSet.create(this.rangeSet);
+        newRangeSet.removeAll(other.rangeSet);
+
+        return new EncodedDiscreteResources(newRangeSet, this.codec);
+    }
+
     boolean isEmpty() {
         return rangeSet.isEmpty();
     }

@@ -50,4 +50,16 @@ public class EncodedDiscreteResourcesTest {
         assertThat(sut.contains(res3), is(false));
     }
 
+    @Test
+    public void testDifference() {
+        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.difference(other), is(EncodedDiscreteResources.of(ImmutableSet.of(res2), new VlanIdCodec())));
+    }
+
 }