Introduce the interface manager as a sub library.

This will want splitting out for other matrix bots to use eventually.
MatrixInterfaceCommand needs decoupling from Mjolnir and then it will
be added too.

src/commands/interface-manager/MatrixRoomReference.ts

@@ -0,0 +1,77 @@
+/**
+ * Copyright (C) 2022 Gnuxie <Gnuxie@protonmail.com>
+ * All rights reserved.
+ */
+
+import { Permalinks, MatrixClient, RoomAlias } from "matrix-bot-sdk";
+
+/**
+ * This is a universal reference for a matrix room.
+ * This is really useful because there are at least 3 ways of referring to a Matrix room,
+ * and some of them require extra steps to be useful in certain contexts (aliases, permalinks).
+ */
+ export class MatrixRoomReference {
+    private constructor(
+        private readonly reference: string,
+        private readonly viaServers: string[] = []
+    ) {
+
+    }
+
+    /**
+     * Join the room using the client provided.
+     * @param client A matrix client that should join the room.
+     * @returns The room id that was joined.
+     */
+    public async joinClient(client: MatrixClient): Promise<string> {
+        return await client.joinRoom(this.reference, this.viaServers);
+    }
+
+    public toPermalink(): string {
+        return Permalinks.forRoom(this.reference, this.viaServers);
+    }
+
+    public static fromAlias(alias: string): MatrixRoomReference {
+        return new MatrixRoomReference(alias);
+    }
+
+    public static fromRoomId(roomId: string, viaServers: string[] = []): MatrixRoomReference {
+        return new MatrixRoomReference(roomId, viaServers);
+    }
+
+    /**
+     * Create a reference from a permalink.
+     * @param permalink A permalink to a matrix room.
+     * @returns A MatrixRoomReference.
+     */
+    public static fromPermalink(permalink: string): MatrixRoomReference {
+        const parts = Permalinks.parseUrl(permalink);
+        return new MatrixRoomReference(parts.roomIdOrAlias, parts.viaServers);
+    }
+
+    /**
+     * Resolves the reference if necessary (ie it is a room alias) and return a new `MatrixRoomReference`.
+     * Maybe in the future this should return a subclass that can only be a RoomID, that will be useful for the config
+     * problems we're having...
+     * @param client A client that we can use to resolve the room alias.
+     * @returns A new MatrixRoomReference that contains the room id.
+     */
+    public async resolve(client: MatrixClient): Promise<MatrixRoomReference> {
+        if (this.reference.startsWith('!')) {
+            return this;
+        } else {
+            const alias = new RoomAlias(this.reference);
+            const roomId = await client.resolveRoom(this.reference);
+            return new MatrixRoomReference(roomId, [alias.domain]);
+        }
+    }
+
+    /**
+     * We don't include a `toRoomId` that uses `forceResolveAlias` as this would erase `viaServers`,
+     * which will be necessary to use if our homeserver hasn't joined the room yet.
+     * @returns A string representing a room id or alias.
+     */
+    public toRoomIdOrAlias(): string {
+        return this.reference;
+    }
+}