Publish cluster-wide AAA stats

Change-Id: Icbdacdae08b6235be022f85eb41ce6d0f8f35a35
diff --git a/api/src/main/java/org/opencord/aaa/AaaStatisticsSnapshot.java b/api/src/main/java/org/opencord/aaa/AaaStatisticsSnapshot.java
new file mode 100644
index 0000000..7d3cfdc
--- /dev/null
+++ b/api/src/main/java/org/opencord/aaa/AaaStatisticsSnapshot.java
@@ -0,0 +1,81 @@
+/*
+ * 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.opencord.aaa;
+
+import com.google.common.base.MoreObjects;
+import com.google.common.collect.ImmutableMap;
+
+/**
+ * Immutable snapshot of AAA statistics.
+ */
+public class AaaStatisticsSnapshot {
+
+    private final ImmutableMap<String, Long> counters;
+
+    /**
+     * Gets the value of a counter.
+     *
+     * @param counterName name of the counter
+     * @return counter value, or 0 if it doesn't exist
+     */
+    public long get(String counterName) {
+        return counters.getOrDefault(counterName, 0L);
+    }
+
+    /**
+     * Creates a new empty snapshot with all counters initialized to 0.
+     */
+    public AaaStatisticsSnapshot() {
+        ImmutableMap.Builder<String, Long> builder = ImmutableMap.builder();
+
+        for (String name : AaaStatistics.COUNTER_NAMES) {
+            builder.put(name, 0L);
+        }
+
+        counters = builder.build();
+    }
+
+    /**
+     * Creates a new snapshot with the given counter values.
+     *
+     * @param counters counter values
+     */
+    public AaaStatisticsSnapshot(ImmutableMap<String, Long> counters) {
+        this.counters = counters;
+    }
+
+    /**
+     * Adds the given snapshot to this snapshot and returns a new snapshot with the aggregate values.
+     *
+     * @param other other snapshot to add to this one
+     * @return new aggregate snapshot
+     */
+    public AaaStatisticsSnapshot add(AaaStatisticsSnapshot other) {
+        ImmutableMap.Builder<String, Long> builder = ImmutableMap.builder();
+
+        counters.forEach((name, value) -> builder.put(name, value + other.counters.get(name)));
+
+        return new AaaStatisticsSnapshot(builder.build());
+    }
+
+    public String toString() {
+        MoreObjects.ToStringHelper helper = MoreObjects.toStringHelper(this.getClass());
+        counters.forEach(helper::add);
+        return helper.toString();
+    }
+
+}