First part of migrating Topo2 to GUI2

Change-Id: I316dd34cba161688e01dfb7b340bff5f2c3c57d4
diff --git a/web/gui2/src/main/webapp/app/view/topology/layer/viewcontroller.ts b/web/gui2/src/main/webapp/app/view/topology/layer/viewcontroller.ts
new file mode 100644
index 0000000..1b40195
--- /dev/null
+++ b/web/gui2/src/main/webapp/app/view/topology/layer/viewcontroller.ts
@@ -0,0 +1,82 @@
+/*
+ * 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.
+ */
+import { FnService, LogService, PrefsService } from 'gui2-fw-lib';
+
+export interface ViewControllerPrefs {
+    visible: string;
+}
+
+/*
+ ONOS GUI -- View Controller.
+ A base class for view controllers to extend from
+ */
+export abstract class ViewControllerImpl {
+    id: string;
+    displayName: string = 'View';
+    name: string;
+    prefs: ViewControllerPrefs;
+    visibility: string;
+
+    constructor(
+        protected fs: FnService,
+        protected log: LogService,
+        protected ps: PrefsService
+    ) {
+        this.log.debug('View Controller constructed');
+    }
+
+    initialize() {
+        this.name = this.displayName.toLowerCase().replace(/ /g, '_');
+        this.prefs = {
+            visible: this.name + '_visible',
+        };
+    }
+
+    enabled() {
+        return this.ps.getPrefs('topo2_prefs', null)[this.prefs.visible];
+    }
+
+    isVisible() {
+        return this.visibility;
+    }
+
+    hide() {
+        this.visibility = 'hidden';
+    }
+
+    show() {
+        this.visibility = 'visible';
+    }
+
+    toggle() {
+        if (this.visibility === 'hidden') {
+            this.visibility = 'visible';
+        } else if (this.visibility === 'visible') {
+            this.visibility = 'hidden';
+        }
+    }
+
+    lookupPrefState(key: string): number {
+        // Return 0 if not defined
+        return this.ps.getPrefs('topo2_prefs', null)[key] || 0;
+    }
+
+    updatePrefState(key: string, value: number) {
+        const state = this.ps.getPrefs('topo2_prefs', null);
+        state[key] = value ? 1 : 0;
+        this.ps.setPrefs('topo2_prefs', state);
+    }
+}