• React UI + Material UI and Apollo Client (cache)
• NestJS + Apollo GraphQL server
• MongoDB as persistence layer, aggregations and pagination

• You need MongoDB running on mongodb://127.0.0.1:27017/chatter. Alternatively, you can use MongoDB Atlas and provide the conection string to MONGODB_URI variable in ./chatter-backend/.env
• Start NestJS backend server: cd ./chatter-backend && nest start
• Start the React application: yarn start

• Feat: when user login automatically is redirected to Home -> In useLogin hook we call client.refetchQueries after a successful user login, which changes the data variable in Auth.tsx (useGetMe hook reexecutes the graphql query) and triggers the useEffect hook that redirects to the Home component

• Feat: when user signup automatically is redirected to Home: Signup.tsx component calls await login({ email, password }) after a successful signup

• Use makeVar from Apollo Client to mantain authentication state and conditionally render the Header components

• Chat.tsx:

  1. When you call the useCreateMessage hook (inside handleCreateMessage), you execute a mutation (CreateMessage) to create a new message. In your useCreateMessage hook, you have an update function that manually updates the Apollo client cache: it reads the current messages from the cache, adds the new message, and writes the updated array back to the cache.
  2. The useMessageCreated hook performs GraphQL websocket subscription and manually updates the Apollo client cache every time a new message is received.
  3. (Moved to ChatList.tsx) useGetMessages hook in your Chat component is subscribed to the messages data in the Apollo cache. It retrieves the current messages in the cache automatically when the cache is updated.
  4. React re-renders the Chat component with the new messages array, so the new message appears in the UI immediately—without a page refresh or manual fetch.

• Update the Apollo Client cache for every latestMessage send to the chat and received from the websocket connection to automatically display it in the ChatListItem as well as the user.name of the sender

• ChatList.tsx react-infinite-scroller, implement infinite scrolling with pagination to fetch more chats. Implement cache policies in apollo client to define the merge behavior of the chats cache field. When you scroll down the Box component, a new query is sent to the chats resolver to fetch the next batch of chats, its sorted in the mongodb aggregation and returned in the correct order to be consumed in the data variable.

• Chat.tsx react-infinite-scroller, implement reverse infinite scrolling with pagination to fetch more chat messages. Implement cache policies in apollo client to define the merge behavior of the messages cache field for each chatId

GraphQL users.resolver.ts forwards the query to the UsersService which calls UsersRepository that extends AbstractEntityRepository that performs CRUD on MongoDB with mongoose ORM

Create a unique index in the users collection on the email field to prevent duplicate emails using database migrations

Strategies are a concept of the passport library. Guards are called before the route is called. Guards need to be changed a bit to work with GraphQL, check gql-auth.guard.ts

auth.controller.ts operates the route /auth/login and uses the LocalAuthGuard which implements the local strategy, receives email and password, validates user in MongoDB and injects JWT as cookie

GqlAuthGuard implements the jwt strategy, which extracts the JWT from the request and validates it or throws Unauthorized 401 exception, GqlAuthGuard is applied to all routes except CreateUser in graphql resolver

GraphQL subscriptions mantain a persistent websocket connection to keep pushing updates to the UI client, when a user enters a chat it stablishes a websocket connection using the chatId

Published messages to GraphQL are filtered by chatId and not sent to the sender (userId) subscription.

ReModel the ChatDocument MongoDB schema as an aggregation of MessageDocument and execute MongoDB aggregations in the chats and messages service layers to operate these schemas

Implement /chats/count and /messages/count REST endpoints with NestJS controllers

Implement pagination with MongoDB aggregations in chats and messages service layers