1 files changed, 138 insertions, 0 deletions
diff --git a/framework/src/onos/core/api/src/main/java/org/onosproject/store/service/Versioned.java b/framework/src/onos/core/api/src/main/java/org/onosproject/store/service/Versioned.java
new file mode 100644
index 00000000..89bd3029
--- /dev/null
+++ b/framework/src/onos/core/api/src/main/java/org/onosproject/store/service/Versioned.java
@@ -0,0 +1,138 @@
+/*
+ * Copyright 2015 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.service;
+
+import java.util.function.Function;
+
+import org.joda.time.DateTime;
+
+import com.google.common.base.MoreObjects;
+import com.google.common.base.Objects;
+
+/**
+ * Versioned value.
+ *
+ * @param <V> value type.
+ */
+public class Versioned<V> {
+
+    private final V value;
+    private final long version;
+    private final long creationTime;
+
+    /**
+     * Constructs a new versioned value.
+     * @param value value
+     * @param version version
+     * @param creationTime milliseconds of the creation event
+     *  from the Java epoch of 1970-01-01T00:00:00Z
+     */
+    public Versioned(V value, long version, long creationTime) {
+        this.value = value;
+        this.version = version;
+        this.creationTime = creationTime;
+    }
+
+    /**
+     * Constructs a new versioned value.
+     * @param value value
+     * @param version version
+     */
+    public Versioned(V value, long version) {
+        this(value, version, System.currentTimeMillis());
+    }
+
+    /**
+     * Returns the value.
+     *
+     * @return value.
+     */
+    public V value() {
+        return value;
+    }
+
+    /**
+     * Returns the version.
+     *
+     * @return version
+     */
+    public long version() {
+        return version;
+    }
+
+    /**
+     * Returns the system time when this version was created.
+     * <p>
+     * Care should be taken when relying on creationTime to
+     * implement any behavior in a distributed setting. Due
+     * to the possibility of clock skew it is likely that
+     * even creationTimes of causally related versions can be
+     * out or order.
+     * @return creation time
+     */
+    public long creationTime() {
+        return creationTime;
+    }
+
+    /**
+     * Maps this instance into another after transforming its
+     * value while retaining the same version and creationTime.
+     * @param transformer function for mapping the value
+     * @param <U> value type of the returned instance
+     * @return mapped instance
+     */
+    public <U> Versioned<U> map(Function<V, U> transformer) {
+        return new Versioned<>(transformer.apply(value), version, creationTime);
+    }
+
+    /**
+     * Returns the value of the specified Versioned object if non-null or else returns
+     * a default value.
+     * @param versioned versioned object
+     * @param defaultValue default value to return if versioned object is null
+     * @param <U> type of the versioned value
+     * @return versioned value or default value if versioned object is null
+     */
+    public static <U> U valueOrElse(Versioned<U> versioned, U defaultValue) {
+        return versioned == null ? defaultValue : versioned.value();
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(value, version, creationTime);
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (!(other instanceof Versioned)) {
+            return false;
+        }
+        Versioned<V> that = (Versioned) other;
+        return Objects.equal(this.value, that.value) &&
+               Objects.equal(this.version, that.version) &&
+               Objects.equal(this.creationTime, that.creationTime);
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(this)
+            .add("value", value)
+            .add("version", version)
+            .add("creationTime", new DateTime(creationTime))
+            .toString();
+    }
+}