Refactor integration manager handling into a common place

It was already in a common place, but this is the boilerplate for supporting multiple integration managers, and multiple integration manager sources. 

For https://github.com/vector-im/riot-web/issues/4913 / https://github.com/vector-im/riot-web/issues/10161

src/integrations/IntegrationManagerInstance.js

@@ -0,0 +1,81 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+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 ScalarAuthClient from "../ScalarAuthClient";
+import sdk from "../index";
+import {dialogTermsInteractionCallback, TermsNotSignedError} from "../Terms";
+import type {Room} from "matrix-js-sdk";
+import Modal from '../Modal';
+
+export class IntegrationManagerInstance {
+    apiUrl: string;
+    uiUrl: string;
+
+    constructor(apiUrl: string, uiUrl: string) {
+        this.apiUrl = apiUrl;
+        this.uiUrl = uiUrl;
+
+        // Per the spec: UI URL is optional.
+        if (!this.uiUrl) this.uiUrl = this.apiUrl;
+    }
+
+    getScalarClient(): ScalarAuthClient {
+        return new ScalarAuthClient(this.apiUrl, this.uiUrl);
+    }
+
+    async open(room: Room = null, screen: string = null, integrationId: string = null): void {
+        const IntegrationsManager = sdk.getComponent("views.settings.IntegrationsManager");
+        const dialog = Modal.createTrackedDialog(
+            'Integration Manager', '', IntegrationsManager,
+            {loading: true}, 'mx_IntegrationsManager',
+        );
+
+        const client = this.getScalarClient();
+        client.setTermsInteractionCallback((policyInfo, agreedUrls) => {
+            // To avoid visual glitching of two modals stacking briefly, we customise the
+            // terms dialog sizing when it will appear for the integrations manager so that
+            // it gets the same basic size as the IM's own modal.
+            return dialogTermsInteractionCallback(
+                policyInfo, agreedUrls, 'mx_TermsDialog_forIntegrationsManager',
+            );
+        });
+
+        let newProps = {};
+        try {
+            await client.connect();
+            if (!client.hasCredentials()) {
+                newProps["connected"] = false;
+            } else {
+                newProps["url"] = client.getScalarInterfaceUrlForRoom(room, screen, integrationId);
+            }
+        } catch (e) {
+            if (e instanceof TermsNotSignedError) {
+                dialog.close();
+                return;
+            }
+
+            console.error(e);
+            props["connected"] = false;
+        }
+
+        // Close the old dialog and open a new one
+        dialog.close();
+        Modal.createTrackedDialog(
+            'Integration Manager', '', IntegrationsManager,
+            newProps, 'mx_IntegrationsManager',
+        );
+    }
+}