Preliminary Scopes Implementation

main/contracts/contracts.ts

@@ -61,6 +61,15 @@ export interface IMessage<T = any> {
  * Represents a messagebroker and provides access to the core features which includes publishing/subscribing to messages and RSVP.
  */
 export interface IMessageBroker<T> {
+    /**
+     * A reference to the parent scope if this is not the root node in the tree of scopes. If this is the root, it's undefined.
+     */
+    readonly parent?: IMessageBroker<T>;
+    /**
+     * A list of all child scopes that have been created on this instance of the broker.
+     */
+    readonly scopes: IMessageBroker<T>[];
+
     /**
      * Creates a new channel with the provided channelName. An optional config object can be passed that specifies how many messages to cache.
      * No caching is set by default
@@ -96,6 +105,14 @@ export interface IMessageBroker<T> {
      * This RSVP function is used by responders and is analogous to the 'Get' function. Responders when invoked must return the required response value type.
      */
     rsvp<K extends keyof RSVPOf<T>>(channelName: K, handler: RSVPHandler<T>): IResponderRef;
+
+    /**
+     * Creates a new scope with the given scopeName with this instance of the MessageBroker as its parent.
+     * If a scope with this name already exists, it returns that instance instead of creating a new one.
+     * @param scopeName The name to use for the scope to create
+     * @returns An instance of the messagebroker that matches the scopeName provided
+     */
+    createScope(scopeName: string): IMessageBroker<T>;
 }
 
 /**

main/core/messagebroker.ts

@@ -1,4 +1,4 @@
-import { get, Injectable } from '@morgan-stanley/needle';
+import { get, getRootInjector, Injectable } from '@morgan-stanley/needle';
 import { defer, Observable, Subject, Subscription } from 'rxjs';
 import { filter, shareReplay } from 'rxjs/operators';
 import { v4 as uuid } from 'uuid';
@@ -29,15 +29,18 @@ export function messagebroker<T = any>(): IMessageBroker<T> {
     return instance;
 }
 
+const rootInjector = getRootInjector();
+
 /**
  * Represents a messagebroker. Using the 'new' operator is discouraged, instead use the messagebroker() function or dependency injection.
  */
 @Injectable()
 export class MessageBroker<T = any> implements IMessageBroker<T> {
     private channelLookup: ChannelModelLookup<T> = {};
     private messagePublisher = new Subject<IMessage<any>>();
+    private _scopes: IMessageBroker<T>[] = [];
 
-    constructor(private rsvpMediator: RSVPMediator<T>) {}
+    constructor(private rsvpMediator: RSVPMediator<T>, private _parent?: IMessageBroker<T>) {}
 
     /**
      * Creates a new channel with the provided channelName. An optional config object can be passed that specifies how many messages to cache.
@@ -99,6 +102,21 @@ export class MessageBroker<T = any> implements IMessageBroker<T> {
         delete this.channelLookup[channelName];
     }
 
+    /**
+     * Creates a new scope with the given scopeName with this instance of the MessageBroker as its parent.
+     * If a scope with this name already exists, it returns that instance instead of creating a new one.
+     * @param scopeName The name to use for the scope to create
+     * @returns An instance of the messagebroker that matches the scopeName provided
+     */
+    public createScope(scopeName: string): IMessageBroker<T> {
+        const scope = rootInjector.createScope(scopeName);
+        scope.registerInstance(MessageBroker, new MessageBroker<T>(new RSVPMediator(), this));
+
+        const instance = scope.get(MessageBroker);
+        this._scopes.push(instance);
+        return instance;
+    }
+
     /**
      * Return a deferred observable as the channel config may have been updated before the subscription
      * @param channelName name of channel to subscribe to
@@ -143,6 +161,7 @@ export class MessageBroker<T = any> implements IMessageBroker<T> {
         }
 
         const publishFunction = (data?: T[K], type?: string): void => {
+            this._scopes.forEach((scope) => scope.create(channelName).publish(data), type);
             this.messagePublisher.next(this.createMessage(channelName, data, type));
         };
 
@@ -180,4 +199,12 @@ export class MessageBroker<T = any> implements IMessageBroker<T> {
     ): channel is RequiredPick<IChannelModel<T[K]>, 'config' | 'subscription'> {
         return channel != null && channel.subscription != null;
     }
+
+    public get parent(): IMessageBroker<T> | undefined {
+        return this._parent;
+    }
+
+    public get scopes(): IMessageBroker<T>[] {
+        return this._scopes;
+    }
 }

spec/core/messagebroker.spec.ts

@@ -368,6 +368,79 @@ describe('MessageBroker', () => {
         });
     });
 
+    describe('Scopes', () => {
+        it('should return a new messagebroker instance when creating a new scope', () => {
+            const instance = getInstance<IMySampleBroker>();
+            const scope = instance.createScope('scope1');
+
+            expect(scope).not.toEqual(instance);
+        });
+
+        it('should return same scope if same name is used', () => {
+            const instance = getInstance<IMySampleBroker>();
+            const scope = instance.createScope('scope1');
+            const sameScope = instance.createScope('scope1');
+
+            expect(scope).toEqual(sameScope);
+        });
+
+        it('should return itself when getting the parent of its child', () => {
+            const instance = getInstance<IMySampleBroker>();
+            const scope = instance.createScope('scope1');
+
+            expect(scope.parent).toEqual(instance);
+        });
+
+        it('should return a list of children scopes via scopes property', () => {
+            const instance = getInstance<IMySampleBroker>();
+            const scope1 = instance.createScope('scope1');
+            const scope2 = instance.createScope('scope2');
+            const scope3 = instance.createScope('scope3');
+
+            expect(instance.scopes).toEqual([scope1, scope2, scope3]);
+        });
+
+        it('should publish messages from parent to children', () => {
+            const parentMessages: Array<IMessage<string>> = [];
+            const childMessages: Array<IMessage<string>> = [];
+            const parent = getInstance();
+            const child = parent.createScope('scope1');
+
+            parent.get('channel').subscribe((message) => parentMessages.push(message));
+            child.get('channel').subscribe((message) => childMessages.push(message));
+
+            parent.create('channel').publish('both should get this');
+            child.create('channel').publish('only the child should get this');
+
+            expect(parentMessages.length).toEqual(1);
+            verifyMessage(parentMessages[0], 'both should get this');
+
+            expect(childMessages.length).toEqual(2);
+            verifyMessage(childMessages[0], 'both should get this');
+            verifyMessage(childMessages[1], 'only the child should get this');
+        });
+
+        it('should not publish messages to "sibling" scopes', () => {
+            const brotherMessages: Array<IMessage<string>> = [];
+            const sisterMessages: Array<IMessage<string>> = [];
+            const parent = getInstance();
+            const brother = parent.createScope('scope1');
+            const sister = parent.createScope('scope2');
+
+            brother.get('channel').subscribe((message) => brotherMessages.push(message));
+            sister.get('channel').subscribe((message) => sisterMessages.push(message));
+
+            brother.create('channel').publish('brother should get this');
+            sister.create('channel').publish('sister should get this');
+
+            expect(brotherMessages.length).toEqual(1);
+            verifyMessage(brotherMessages[0], 'brother should get this');
+
+            expect(sisterMessages.length).toEqual(1);
+            verifyMessage(sisterMessages[0], 'sister should get this');
+        });
+    });
+
     function verifyMessage<T>(message: IMessage<T>, expectedData: T, expectedType?: string) {
         expect(message).toBeDefined();
         expect(message.data).toEqual(expectedData);