Add atomic mastership/term/backups method to MastershipService

Change-Id: I18c3aeaa5101c9ce08ff38fffd70eaec903a0f3e
diff --git a/core/api/src/main/java/org/onosproject/mastership/MastershipInfo.java b/core/api/src/main/java/org/onosproject/mastership/MastershipInfo.java
new file mode 100644
index 0000000..c9a4f0e
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/mastership/MastershipInfo.java
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.mastership;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import org.onosproject.cluster.NodeId;
+import org.onosproject.net.MastershipRole;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
+
+/**
+ * Mastership info.
+ */
+public final class MastershipInfo {
+    private final long term;
+    private final Optional<NodeId> master;
+    private final ImmutableMap<NodeId, MastershipRole> roles;
+
+    public MastershipInfo() {
+        this(0, Optional.empty(), ImmutableMap.of());
+    }
+
+    public MastershipInfo(long term, Optional<NodeId> master, ImmutableMap<NodeId, MastershipRole> roles) {
+        this.term = term;
+        this.master = master;
+        this.roles = roles;
+    }
+
+    /**
+     * Returns the mastership term.
+     *
+     * @return the mastership term
+     */
+    public long term() {
+        return term;
+    }
+
+    /**
+     * Returns the current master.
+     *
+     * @return the current master
+     */
+    public Optional<NodeId> master() {
+        return master;
+    }
+
+    /**
+     * Returns a sorted list of standby nodes.
+     *
+     * @return a sorted list of standby nodes
+     */
+    public List<NodeId> backups() {
+        return getRoles(MastershipRole.STANDBY);
+    }
+
+    /**
+     * Returns the list of nodes with the given role.
+     *
+     * @param role the role by which to filter nodes
+     * @return an immutable list of nodes with the given role sorted in priority order
+     */
+    public List<NodeId> getRoles(MastershipRole role) {
+        return ImmutableList.copyOf(roles.entrySet()
+            .stream()
+            .filter(entry -> entry.getValue() == role)
+            .map(Map.Entry::getKey)
+            .collect(Collectors.toList()));
+    }
+
+    /**
+     * Returns the current role for the given node.
+     *
+     * @param nodeId the node for which to return the current role
+     * @return the current role for the given node
+     */
+    public MastershipRole getRole(NodeId nodeId) {
+        return roles.get(nodeId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(term, master, roles);
+    }
+
+    @Override
+    public boolean equals(Object object) {
+        if (object instanceof MastershipInfo) {
+            MastershipInfo that = (MastershipInfo) object;
+            return this.term == that.term
+                && Objects.equals(this.master, that.master)
+                && Objects.equals(this.roles, that.roles);
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return toStringHelper(this)
+            .add("term", term)
+            .add("master", master)
+            .add("roles", roles)
+            .toString();
+    }
+}