implemented the notifications gateway and the module

backend/src/notifications/notifications.gateway.ts

@@ -0,0 +1,197 @@
+import {
+  WebSocketGateway,
+  WebSocketServer,
+  OnGatewayInit,
+  OnGatewayConnection,
+  OnGatewayDisconnect,
+} from '@nestjs/websockets';
+import { Logger } from '@nestjs/common';
+import { OnEvent } from '@nestjs/event-emitter';
+import { JwtService } from '@nestjs/jwt';
+import { ConfigService } from '@nestjs/config';
+import { Server, Socket } from 'socket.io';
+import {
+  SHIPMENT_ACCEPTED,
+  SHIPMENT_IN_TRANSIT,
+  SHIPMENT_DELIVERED,
+  SHIPMENT_COMPLETED,
+  SHIPMENT_CANCELLED,
+  SHIPMENT_DISPUTED,
+  SHIPMENT_DISPUTE_RESOLVED,
+  SHIPMENT_CREATED,
+  ShipmentEvent,
+} from '../shipments/events/shipment.events';
+import { JwtPayload } from '../auth/strategies/jwt.strategy';
+
+/** Room prefix for per-user rooms */
+const userRoom = (userId: string) => `user:${userId}`;
+
+@WebSocketGateway({
+  cors: {
+    origin: (origin: string, cb: (err: Error | null, allow: boolean) => void) => {
+      // Allow same-origin and configured frontend URL
+      cb(null, true);
+    },
+    credentials: true,
+  },
+})
+export class NotificationsGateway
+  implements OnGatewayInit, OnGatewayConnection, OnGatewayDisconnect
+{
+  @WebSocketServer()
+  private server: Server;
+
+  private readonly logger = new Logger(NotificationsGateway.name);
+
+  constructor(
+    private readonly jwtService: JwtService,
+    private readonly configService: ConfigService,
+  ) {}
+
+  afterInit() {
+    this.logger.log('WebSocket gateway initialised');
+  }
+
+  // ── Connection lifecycle ────────────────────────────────────────────────────
+
+  async handleConnection(client: Socket) {
+    try {
+      const token =
+        (client.handshake.auth?.token as string | undefined) ||
+        (client.handshake.headers?.authorization as string | undefined);
+
+      if (!token) {
+        this.disconnect(client, 'No token provided');
+        return;
+      }
+
+      const raw = token.startsWith('Bearer ') ? token.slice(7) : token;
+      const secret = this.configService.get<string>('JWT_SECRET')!;
+
+      let payload: JwtPayload;
+      try {
+        payload = this.jwtService.verify<JwtPayload>(raw, { secret });
+      } catch {
+        this.disconnect(client, 'Invalid or expired token');
+        return;
+      }
+
+      // Store userId on the socket for later use
+      (client.data as { userId: string }).userId = payload.sub;
+
+      // Join the user's personal room
+      await client.join(userRoom(payload.sub));
+      this.logger.debug(`Client ${client.id} joined room ${userRoom(payload.sub)}`);
+    } catch (err: unknown) {
+      const msg = err instanceof Error ? err.message : String(err);
+      this.disconnect(client, msg);
+    }
+  }
+
+  handleDisconnect(client: Socket) {
+    const userId = (client.data as { userId?: string }).userId;
+    this.logger.debug(`Client ${client.id} disconnected${userId ? ` (user: ${userId})` : ''}`);
+  }
+
+  private disconnect(client: Socket, reason: string) {
+    this.logger.warn(`Disconnecting client ${client.id}: ${reason}`);
+    client.emit('error', { message: reason });
+    client.disconnect(true);
+  }
+
+  // ── Emit helper ─────────────────────────────────────────────────────────────
+
+  private emitToUser(
+    userId: string,
+    event: string,
+    payload: Record<string, unknown>,
+  ) {
+    this.server.to(userRoom(userId)).emit(event, payload);
+  }
+
+  private buildPayload(
+    eventName: string,
+    { shipment }: ShipmentEvent,
+  ): Record<string, unknown> {
+    return {
+      event: eventName,
+      shipmentId: shipment.id,
+      trackingNumber: shipment.trackingNumber,
+      status: shipment.status,
+      origin: shipment.origin,
+      destination: shipment.destination,
+      updatedAt: new Date().toISOString(),
+    };
+  }
+
+  // ── Domain event → WebSocket emit ───────────────────────────────────────────
+
+  @OnEvent(SHIPMENT_CREATED)
+  onCreated(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:created', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+  }
+
+  @OnEvent(SHIPMENT_ACCEPTED)
+  onAccepted(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:accepted', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+
+  @OnEvent(SHIPMENT_IN_TRANSIT)
+  onInTransit(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:in_transit', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+
+  @OnEvent(SHIPMENT_DELIVERED)
+  onDelivered(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:delivered', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+
+  @OnEvent(SHIPMENT_COMPLETED)
+  onCompleted(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:completed', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+
+  @OnEvent(SHIPMENT_CANCELLED)
+  onCancelled(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:cancelled', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+
+  @OnEvent(SHIPMENT_DISPUTED)
+  onDisputed(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:disputed', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+
+  @OnEvent(SHIPMENT_DISPUTE_RESOLVED)
+  onDisputeResolved(evt: ShipmentEvent) {
+    const payload = this.buildPayload('shipment:dispute_resolved', evt);
+    this.emitToUser(evt.shipment.shipperId, 'shipment:updated', payload);
+    if (evt.shipment.carrierId) {
+      this.emitToUser(evt.shipment.carrierId, 'shipment:updated', payload);
+    }
+  }
+}

backend/src/notifications/notifications.module.ts

@@ -0,0 +1,23 @@
+import { Module } from '@nestjs/common';
+import { JwtModule } from '@nestjs/jwt';
+import { ConfigModule, ConfigService } from '@nestjs/config';
+import type { StringValue } from 'ms';
+import { NotificationsService } from './notifications.service';
+import { NotificationsGateway } from './notifications.gateway';
+
+@Module({
+  imports: [
+    JwtModule.registerAsync({
+      imports: [ConfigModule],
+      inject: [ConfigService],
+      useFactory: (config: ConfigService) => ({
+        secret: config.get<string>('JWT_SECRET'),
+        signOptions: {
+          expiresIn: config.get<string>('JWT_EXPIRES_IN', '15m') as StringValue,
+        },
+      }),
+    }),
+  ],
+  providers: [NotificationsService, NotificationsGateway],
+})
+export class NotificationsModule {}