support "disabled" rules for Viewer extensions

docs/extending/application-features.md

@@ -420,6 +420,22 @@ Every custom component receives the following properties at runtime:
 | url       | string                 | File content URL.           |
 | extension | string                 | File name extension.        |
 
+#### Rules
+
+You can also provide a rule for the `disabled` state.
+That allows to provide conditional availability for Viewer extensions based on external factors.
+
+```json
+{
+  "id": "app.viewer.pdf",
+  "fileExtension": "png",
+  "component": "app.components.tabs.metadata",
+  "rules": {
+    "disabled": "isViewerDisabled"
+  }
+}
+```
+
 ### Toolbar actions
 
 The default toolbar actions from the ACA viewer can be customized through extensions to be replaced, modified or disabled.

src/app/extensions/extension.service.ts

@@ -153,10 +153,11 @@ export class AppExtensionService implements AppRuleContext {
       config,
       'features.viewer.shared.toolbarActions'
     );
-    this.viewerContentExtensions = this.loader.getElements<ViewerExtensionRef>(
+
-      config,
+    this.viewerContentExtensions = this.loader
-      'features.viewer.content'
+      .getElements<ViewerExtensionRef>(config, 'features.viewer.content')
-    );
+      .filter(ref => !this.isViewerExtensionDisabled(ref));
+
     this.contextMenuActions = this.loader.getContentActions(
       config,
       'features.contextMenu'
@@ -457,6 +458,20 @@ export class AppExtensionService implements AppRuleContext {
     return true;
   }
 
+  isViewerExtensionDisabled(extension: any): boolean {
+    if (extension) {
+      if (extension.disabled) {
+        return true;
+      }
+
+      if (extension.rules && extension.rules.disabled) {
+        return this.extensions.evaluateRule(extension.rules.disabled, this);
+      }
+    }
+
+    return false;
+  }
+
   runActionById(id: string) {
     const action = this.extensions.getActionById(id);
     if (action) {