Add GraphQL Subscription Support for Real-Time Updates

[llinsss]

Problem

Current GraphQL implementation only supports queries and mutations. Need subscriptions for real-time updates on transactions, balances, and notifications.

Proposed Solution

Add GraphQL subscriptions using WebSocket transport for real-time data streaming.

Technical Implementation

New Files:

• backend/graphql/subscriptions.js - Subscription definitions
• backend/graphql/pubsub.js - PubSub implementation
• backend/tests/graphql.subscription.test.js - Subscription tests

Modify:

• backend/graphql/schema.js - Add subscription types
• backend/graphql/resolvers.js - Add subscription resolvers
• backend/graphql/apollo.js - Configure WebSocket support
• backend/services/SocketService.js - Integrate with GraphQL subscriptions
• backend/controllers/transactionController.js - Publish events

Subscription Schema

type Subscription {
  transactionUpdated(userId: ID!): Transaction
  balanceChanged(userId: ID!, chain: String!): Balance
  notificationReceived(userId: ID!): Notification
  priceUpdated(token: String!): TokenPrice
  tagRegistered: Tag
}

# Usage example
subscription {
  transactionUpdated(userId: "123") {
    id
    status
    amount
    from
    to
    timestamp
  }
}

Acceptance Criteria

• WebSocket transport configured
• Subscriptions for transactions, balances, notifications
• PubSub with Redis backend
• Authentication for subscriptions
• Connection management and cleanup
• Subscription filtering
• Test coverage > 80%

Priority

Medium - Enhances real-time capabilities