Concrete Mediator (ChatMediator):?

• The ChatMediator class is the concrete mediator that implements

IChatMediator. It manages a list of users and is responsible for

broadcasting messages to all registered users, except the one who sent the

message.

• The mediator decouples the user objects from each other, so they don't need

to know about each other's existence.

public class ChatMediator : IChatMediator

private readonly List<User> _users = new List<User>();

public void RegisterUser(User user) => _users.Add(user);

Follow:

public void SendMessage(string message, User user)

foreach (var u in _users)

// Message should not be sent to the user who sent it

if (u != user)

u.Receive(message);