Adding support for user interface extensions.

Change-Id: I1e41d16efc11be31ad4c2fb0c09e86e3dfd26706
diff --git a/web/gui/src/main/java/org/onosproject/ui/impl/UiExtensionManager.java b/web/gui/src/main/java/org/onosproject/ui/impl/UiExtensionManager.java
new file mode 100644
index 0000000..6ca1e21
--- /dev/null
+++ b/web/gui/src/main/java/org/onosproject/ui/impl/UiExtensionManager.java
@@ -0,0 +1,96 @@
+/*
+ * 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.ui.impl;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Service;
+import org.onosproject.ui.UiExtension;
+import org.onosproject.ui.UiExtensionService;
+import org.onosproject.ui.UiView;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+import java.util.Map;
+
+import static com.google.common.collect.ImmutableList.of;
+import static java.util.stream.Collectors.toSet;
+
+/**
+ * Manages the user interface extensions.
+ */
+@Component(immediate = true)
+@Service
+public class UiExtensionManager implements UiExtensionService {
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    // List of all extensions
+    private final List<UiExtension> extensions = Lists.newArrayList();
+
+    // Map of views to extensions
+    private final Map<String, UiExtension> views = Maps.newHashMap();
+
+    // Core views & core extension
+    private final List<UiView> coreViews = of(new UiView("sample", "Sample"),
+                                              new UiView("topo", "Topology View"),
+                                              new UiView("device", "Devices"));
+
+    private final UiExtension core = new UiExtension(coreViews, getClass().getClassLoader());
+
+    @Activate
+    public void activate() {
+        register(core);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        unregister(core);
+        log.info("Stopped");
+    }
+
+    @Override
+    public synchronized void register(UiExtension extension) {
+        if (!extensions.contains(extension)) {
+            extensions.add(extension);
+            for (UiView view : extension.views()) {
+                views.put(view.id(), extension);
+            }
+        }
+    }
+
+    @Override
+    public synchronized void unregister(UiExtension extension) {
+        extensions.remove(extension);
+        extension.views().stream().map(UiView::id).collect(toSet()).forEach(views::remove);
+    }
+
+    @Override
+    public synchronized List<UiExtension> getExtensions() {
+        return ImmutableList.copyOf(extensions);
+    }
+
+    @Override
+    public synchronized UiExtension getViewExtension(String viewId) {
+        return views.get(viewId);
+    }
+}