Extract start DM logic to a helper file (#8317)

* Extract start DM logic to a helper file

* Fix incorrect import

src/utils/direct-messages.ts

@@ -14,11 +14,18 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { IInvite3PID } from "matrix-js-sdk/src/@types/requests";
 import { MatrixClient } from "matrix-js-sdk/src/client";
 import { Room } from "matrix-js-sdk/src/models/room";
 
+import createRoom, { canEncryptToAllUsers } from "../createRoom";
+import { Action } from "../dispatcher/actions";
+import { ViewRoomPayload } from "../dispatcher/payloads/ViewRoomPayload";
+import { getAddressType } from "../UserAddress";
 import DMRoomMap from "./DMRoomMap";
 import { isJoinedOrNearlyJoined } from "./membership";
+import dis from "../dispatcher/dispatcher";
+import { privateShouldBeEncrypted } from "./rooms";
 
 export function findDMForUser(client: MatrixClient, userId: string): Room {
     const roomIds = DMRoomMap.shared().getDMRoomsForUserId(userId);
@@ -44,3 +51,152 @@ export function findDMForUser(client: MatrixClient, userId: string): Room {
         return suitableDMRooms[0];
     }
 }
+
+export async function startDm(client: MatrixClient, targets: Member[]): Promise<void> {
+    const targetIds = targets.map(t => t.userId);
+
+    // Check if there is already a DM with these people and reuse it if possible.
+    let existingRoom: Room;
+    if (targetIds.length === 1) {
+        existingRoom = findDMForUser(client, targetIds[0]);
+    } else {
+        existingRoom = DMRoomMap.shared().getDMRoomForIdentifiers(targetIds);
+    }
+    if (existingRoom) {
+        dis.dispatch<ViewRoomPayload>({
+            action: Action.ViewRoom,
+            room_id: existingRoom.roomId,
+            should_peek: false,
+            joining: false,
+            metricsTrigger: "MessageUser",
+        });
+        return;
+    }
+
+    const createRoomOptions = { inlineErrors: true } as any; // XXX: Type out `createRoomOptions`
+
+    if (privateShouldBeEncrypted()) {
+        // Check whether all users have uploaded device keys before.
+        // If so, enable encryption in the new room.
+        const has3PidMembers = targets.some(t => t instanceof ThreepidMember);
+        if (!has3PidMembers) {
+            const allHaveDeviceKeys = await canEncryptToAllUsers(client, targetIds);
+            if (allHaveDeviceKeys) {
+                createRoomOptions.encryption = true;
+            }
+        }
+    }
+
+    // Check if it's a traditional DM and create the room if required.
+    // TODO: [Canonical DMs] Remove this check and instead just create the multi-person DM
+    const isSelf = targetIds.length === 1 && targetIds[0] === client.getUserId();
+    if (targetIds.length === 1 && !isSelf) {
+        createRoomOptions.dmUserId = targetIds[0];
+    }
+
+    if (targetIds.length > 1) {
+        createRoomOptions.createOpts = targetIds.reduce(
+            (roomOptions, address) => {
+                const type = getAddressType(address);
+                if (type === 'email') {
+                    const invite: IInvite3PID = {
+                        id_server: client.getIdentityServerUrl(true),
+                        medium: 'email',
+                        address,
+                    };
+                    roomOptions.invite_3pid.push(invite);
+                } else if (type === 'mx-user-id') {
+                    roomOptions.invite.push(address);
+                }
+                return roomOptions;
+            },
+            { invite: [], invite_3pid: [] },
+        );
+    }
+
+    await createRoom(createRoomOptions);
+}
+
+// This is the interface that is expected by various components in the Invite Dialog and RoomInvite.
+// It is a bit awkward because it also matches the RoomMember class from the js-sdk with some extra support
+// for 3PIDs/email addresses.
+export abstract class Member {
+    /**
+     * The display name of this Member. For users this should be their profile's display
+     * name or user ID if none set. For 3PIDs this should be the 3PID address (email).
+     */
+    public abstract get name(): string;
+
+    /**
+     * The ID of this Member. For users this should be their user ID. For 3PIDs this should
+     * be the 3PID address (email).
+     */
+    public abstract get userId(): string;
+
+    /**
+     * Gets the MXC URL of this Member's avatar. For users this should be their profile's
+     * avatar MXC URL or null if none set. For 3PIDs this should always be null.
+     */
+    public abstract getMxcAvatarUrl(): string;
+}
+
+export class DirectoryMember extends Member {
+    private readonly _userId: string;
+    private readonly displayName?: string;
+    private readonly avatarUrl?: string;
+
+    // eslint-disable-next-line camelcase
+    constructor(userDirResult: { user_id: string, display_name?: string, avatar_url?: string }) {
+        super();
+        this._userId = userDirResult.user_id;
+        this.displayName = userDirResult.display_name;
+        this.avatarUrl = userDirResult.avatar_url;
+    }
+
+    // These next class members are for the Member interface
+    get name(): string {
+        return this.displayName || this._userId;
+    }
+
+    get userId(): string {
+        return this._userId;
+    }
+
+    getMxcAvatarUrl(): string {
+        return this.avatarUrl;
+    }
+}
+
+export class ThreepidMember extends Member {
+    private readonly id: string;
+
+    constructor(id: string) {
+        super();
+        this.id = id;
+    }
+
+    // This is a getter that would be falsey on all other implementations. Until we have
+    // better type support in the react-sdk we can use this trick to determine the kind
+    // of 3PID we're dealing with, if any.
+    get isEmail(): boolean {
+        return this.id.includes('@');
+    }
+
+    // These next class members are for the Member interface
+    get name(): string {
+        return this.id;
+    }
+
+    get userId(): string {
+        return this.id;
+    }
+
+    getMxcAvatarUrl(): string {
+        return null;
+    }
+}
+
+export interface IDMUserTileProps {
+    member: Member;
+    onRemove(member: Member): void;
+}