feat: add a shared state as a server.io property

and send it to the new connected clients

package.json

@@ -24,6 +24,7 @@
   },
   "dependencies": {
     "@hapi/joi": "^17.1.0",
+    "automerge": "^0.12.1",
     "express": "^4.17.1",
     "nanoid": "^2.1.9",
     "randomcolor": "^0.5.4",

src/domain/events/toclient/event.to.client.ts

@@ -1,6 +1,7 @@
 export class EventToClient {
   // static readonly RoomGuestsList = 'room-guests-list'
 
+  static readonly State = 'state'
   static readonly UsersList = 'users-list'
 
   static readonly InternalServerError = 'internal-server-error'

src/domain/events/toclient/index.ts

@@ -1,5 +1,6 @@
 // export * from "./room.guests.list.event";
 
+export * from './state.event'
 export * from './users.list.event'
 
 export * from './internal.server.error.event'

src/socket.io/socket.spec.ts

@@ -11,7 +11,7 @@ import {
   UpdateUserNameEvent,
   UpdateUserColorEvent,
 } from '../domain/events/toserver'
-import { UsersListEvent } from '../domain/events/toclient'
+import { StateEvent, UsersListEvent } from '../domain/events/toclient'
 import { ExportedUser } from '../domain'
 
 const socketUrl: string = 'http://localhost:5000'
@@ -92,6 +92,19 @@ describe('Server', () => {
           // after
           newClient.disconnect()
         })
+        it('should send an empty state to a new user meanwhile the state has not been changed', async () => {
+          // arrange
+          const getStateEvent = (): Promise<object> =>
+            new Promise(resolve =>
+              passiveClient.on(StateEvent.eventName, resolve)
+            )
+
+          // act
+          const state = await getStateEvent()
+
+          // assert
+          expect(state).to.deep.equal({})
+        })
       })
 
       describe('update-user-name', () => {

src/socket.io/socket.ts

@@ -1,15 +1,17 @@
+import Automerge from 'automerge'
 import { Constants } from './constants'
 import { Guard, ConsoleLogger } from '../shared/index'
 import {
   ConnectionEvent,
   UpdateUserNameEvent,
   UpdateUserColorEvent,
 } from '../domain/events/toserver'
-import { UsersListEvent } from '../domain/events/toclient'
+import { StateEvent, UsersListEvent } from '../domain/events/toclient'
 import { ExportedUser, User } from '../domain'
 
 class Socket {
   private users: Map<SocketIOClient.Socket['id'], User> = new Map()
+  private state = Automerge.init()
 
   constructor(private io: SocketIO.Server, private log = new ConsoleLogger()) {}
 
@@ -22,6 +24,7 @@ class Socket {
         // connections
         const socketUser: User = this.createUser(socket.id)
         this.emitUsersListToAll()
+        this.emitStateToUser(socket)
 
         socket.on(
           UpdateUserNameEvent.eventName,
@@ -169,6 +172,19 @@ class Socket {
     return [...this.users.values()].map(user => user.export())
   }
 
+  private emitStateToUser(socket: SocketIOClient.Socket) {
+    const stateEvent = new StateEvent(this.stateAsJson)
+    socket.emit(StateEvent.eventName, stateEvent.state)
+  }
+
+  // TODO: maybe the return type should be "any" as for the JOSN.parse function
+  // https://github.com/MazeChaZer/TypeScript/blob/master/src/lib/es5.d.ts#L966
+  private get stateAsJson(): object {
+    // No need to send the metadata, that could be heavy
+    // This means that the history is not included
+    return JSON.parse(JSON.stringify(this.state))
+  }
+
   private toException = (error: Error): Exception => {
     return {
       message: error.message,