Separate ResourceStore into stores for discrete and continuous type

This is a preliminary work for ONOS-4281.

Change-Id: Ifed9c761eb16f6a249a9d069948edc7421301617
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/ResourceStoreUtil.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/ResourceStoreUtil.java
new file mode 100644
index 0000000..3b2c324
--- /dev/null
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/ResourceStoreUtil.java
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.store.resource.impl;
+
+import org.onosproject.net.resource.ContinuousResource;
+
+final class ResourceStoreUtil {
+    // prohibit construction
+    private ResourceStoreUtil() {}
+
+    /**
+     * Checks if there is enough resource volume to allocated the requested resource
+     * against the specified resource.
+     *
+     * @param original   original resource
+     * @param request    requested resource
+     * @param allocation current allocation of the resource
+     * @return true if there is enough resource volume. Otherwise, false.
+     */
+    // computational complexity: O(n) where n is the number of allocations
+    static boolean hasEnoughResource(ContinuousResource original,
+                                     ContinuousResource request,
+                                     ConsistentResourceStore.ContinuousResourceAllocation allocation) {
+        if (allocation == null) {
+            return request.value() <= original.value();
+        }
+
+        double allocated = allocation.allocations().stream()
+                .filter(x -> x.resource() instanceof ContinuousResource)
+                .map(x -> (ContinuousResource) x.resource())
+                .mapToDouble(ContinuousResource::value)
+                .sum();
+        double left = original.value() - allocated;
+        return request.value() <= left;
+    }
+}