Add a command for creating custom widgets without an integration manager

Fixes https://github.com/vector-im/riot-web/issues/4882

src/SlashCommands.js

@@ -29,6 +29,7 @@ import * as querystring from "querystring";
 import MultiInviter from './utils/MultiInviter';
 import { linkifyAndSanitizeHtml } from './HtmlUtils';
 import QuestionDialog from "./components/views/dialogs/QuestionDialog";
+import WidgetUtils from "./utils/WidgetUtils";
 
 class Command {
     constructor({name, args='', description, runFn, hideCompletionAfterSpace=false}) {
@@ -606,6 +607,26 @@ export const CommandMap = {
         },
     }),
 
+    addwidget: new Command({
+        name: 'addwidget',
+        args: '<url>',
+        description: _td('Adds a custom widget by URL to the room'),
+        runFn: function(roomId, args) {
+            if (!args || (!args.startsWith("https://") && !args.startsWith("http://"))) {
+                return reject(_t("Please supply a https:// or http:// widget URL"));
+            }
+            if (WidgetUtils.canUserModifyWidgets(roomId)) {
+                const userId = MatrixClientPeg.get().getUserId();
+                const nowMs = (new Date()).getTime();
+                const widgetId = encodeURIComponent(`${roomId}_${userId}_${nowMs}`);
+                return success(WidgetUtils.setRoomWidget(
+                    roomId, widgetId, "customwidget", args, "Custom Widget", {}));
+            } else {
+                return reject(_t("You cannot modify widgets in this room."));
+            }
+        },
+    }),
+
     // Verify a user, device, and pubkey tuple
     verify: new Command({
         name: 'verify',

src/i18n/strings/en_EN.json

@@ -161,6 +161,9 @@
     "Define the power level of a user": "Define the power level of a user",
     "Deops user with given id": "Deops user with given id",
     "Opens the Developer Tools dialog": "Opens the Developer Tools dialog",
+    "Adds a custom widget by URL to the room": "Adds a custom widget by URL to the room",
+    "Please supply a https:// or http:// widget URL": "Please supply a https:// or http:// widget URL",
+    "You cannot modify widgets in this room.": "You cannot modify widgets in this room.",
     "Verifies a user, device, and pubkey tuple": "Verifies a user, device, and pubkey tuple",
     "Unknown (user, device) pair:": "Unknown (user, device) pair:",
     "Device already verified!": "Device already verified!",