Move spec permalinks into their own class

This allows for Riot permalinks to be introduced without if-else ladders everywhere.

src/utils/permalinks/SpecPermalinkConstructor.js

@@ -0,0 +1,50 @@
+/*
+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 PermalinkConstructor from "./PermalinkConstructor";
+
+export const host = "matrix.to";
+export const baseUrl = `https://${host}`;
+
+/**
+ * Generates matrix.to permalinks
+ */
+export default class SpecPermalinkConstructor extends PermalinkConstructor {
+    constructor() {
+        super();
+    }
+
+    forEvent(roomId: string, eventId: string, serverCandidates: string[]): string {
+        return `${baseUrl}/#/${roomId}/${eventId}${this.encodeServerCandidates(serverCandidates)}`;
+    }
+
+    forRoom(roomIdOrAlias: string, serverCandidates: string[]): string {
+        return `${baseUrl}/#/${roomIdOrAlias}${this.encodeServerCandidates(serverCandidates)}`;
+    }
+
+    forUser(userId: string): string {
+        return `${baseUrl}/#/${userId}`;
+    }
+
+    forGroup(groupId: string): string {
+        return `${baseUrl}/#/${groupId}`;
+    }
+
+    encodeServerCandidates(candidates: string[]) {
+        if (!candidates || candidates.length === 0) return '';
+        return `?via=${candidates.map(c => encodeURIComponent(c)).join("&via=")}`;
+    }
+}