ONOS-5449 Implemented skeleton of OFAgent application

Change-Id: Ie6c719872549a004471e466a43a2b531bc48b231
diff --git a/apps/ofagent/src/main/java/org/onosproject/ofagent/api/OFAgent.java b/apps/ofagent/src/main/java/org/onosproject/ofagent/api/OFAgent.java
new file mode 100644
index 0000000..b44f48e
--- /dev/null
+++ b/apps/ofagent/src/main/java/org/onosproject/ofagent/api/OFAgent.java
@@ -0,0 +1,108 @@
+/*
+ * Copyright 2017-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.ofagent.api;
+
+import io.netty.channel.nio.NioEventLoopGroup;
+import org.onosproject.incubator.net.virtual.NetworkId;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+
+/**
+ * Representation of an OF agent, which brokers virtual devices and external
+ * controllers by handling OpenFlow connections and messages between them.
+ */
+public interface OFAgent {
+
+    /**
+     * Returns the identifier of the virtual network that this agent cares for.
+     *
+     * @return id of the virtual network
+     */
+    NetworkId networkId();
+
+    /**
+     * Returns the external OpenFlow controllers of the virtual network.
+     *
+     * @return set of openflow controllers
+     */
+    Set<OFController> controllers();
+
+    /**
+     * Starts the OpenFlow agent.
+     */
+    void start();
+
+    /**
+     * Stops the OpenFlow agent.
+     */
+    void stop();
+
+    /**
+     * Builder of OF agent entities.
+     */
+    interface Builder {
+
+        /**
+         * Returns new OF agent.
+         *
+         * @return of agent
+         */
+        OFAgent build();
+
+        /**
+         * Returns OF agent builder with the supplied network ID.
+         *
+         * @param networkId id of the virtual network
+         * @return of agent builder
+         */
+        Builder networkId(NetworkId networkId);
+
+        /**
+         * Returns OF agent builder with the supplied network services for the
+         * virtual network.
+         *
+         * @param services network services for the virtual network
+         * @return of agent builder
+         */
+        Builder services(Map<Class<?>, Object> services);
+
+        /**
+         * Returns OF agent builder with the supplied controllers.
+         *
+         * @param controllers set of openflow controllers
+         * @return of agent builder
+         */
+        Builder controllers(Set<OFController> controllers);
+
+        /**
+         * Returns OF agent builder with the supplied event executor.
+         *
+         * @param eventExecutor event executor
+         * @return of agent builder
+         */
+        Builder eventExecutor(ExecutorService eventExecutor);
+
+        /**
+         * Returns OF agent builder with the supplied IO work group.
+         *
+         * @param ioWorker io worker group
+         * @return of agent builder
+         */
+        Builder ioWorker(NioEventLoopGroup ioWorker);
+    }
+}