Extend some user-related models and implement private messaging

[uxabix]

We need to extend the messaging system to support private 1-on-1 chats and implement the ability to block users, while maintaining compatibility with existing lobby and general chat functionality.

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Requirements

Model Extensions

• Create a new Chat model to handle different types of chats:
  • Private 1-on-1 chats
  • Lobby-linked chats
  • General/global chats
• Refactor or update the existing Message model to reference the new Chat model.
• Implement a mechanism to block users, preventing messages from blocked users from being delivered. Possible approaches:
  • Introduce a BlockedUser model linking two users.
  • Add a blocked_users ManyToMany field on the User model.
  • Enforce block logic in message sending at the model or API layer.
• Ensure backward compatibility with existing chat types (lobby/general).

Private Messaging

• Implement 1-on-1 private messaging between users.
• Messages must be stored in the database and retrievable via API.
• [] Ensure blocked users cannot send messages to the blocker.
• Optional: prepare for future group chat implementation, but focus on 1-on-1 messaging first.

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Technical Details

• Use Django models and REST API for message storage and retrieval.
• The Chat model should track participants and chat type.
• Ensure database integrity: avoid duplicate chat instances for the same user pair.
• Implement blocking logic at the model or API level.
• Maintain compatibility with current lobby/general chat features.

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Testing

• Verify private messages can be sent and received correctly.
• Confirm blocked users cannot send messages to the blocker.
• Ensure lobby and general chat functionality is unaffected.
• Test edge cases like sending messages to oneself or attempting to message a blocked user.
• Verify database consistency for Chat and Message models.

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Definition of Done

• Chat model created and integrated with messages.
• [ x Private 1-on-1 messaging implemented and functional.
• User blocking functionality enforced in messaging.
• Existing lobby/general chat system remains compatible.
• API endpoints allow sending and retrieving private messages.
• Tests confirm correct behavior for messaging and blocking.
• Documentation updated with model changes and API usage.