using System;

using System.Collections.Generic;

​

// Mediator interface

public interface IChatRoom

{

    void SendMessage(string message, string senderName);

    void RegisterUser(User user);

}

​

// Concrete mediator class (Chat Room)

public class ChatRoom : IChatRoom

{

    private readonly Dictionary<string, User> users = new Dictionary<string, User>();

​

    public void SendMessage(string message, string senderName)

    {

        if (users.TryGetValue(senderName, out User sender))

        {

            foreach (var user in users.Values)

            {

                if (user != sender)

                {

                    user.ReceiveMessage(message, senderName);

                }

            }

        }

    }

​

    public void RegisterUser(User user)

    {

        if (!users.ContainsKey(user.Name))

        {

            users.Add(user.Name, user);

        }

    }

}

​

// Colleague interface

public abstract class User

{

    protected IChatRoom chatRoom;

    public string Name { get; private set; }

​

    public User(string name, IChatRoom chatRoom)

    {

        Name = name;

        this.chatRoom = chatRoom;

        chatRoom.RegisterUser(this);

    }

​

    public abstract void Send(string message);

    public abstract void ReceiveMessage(string message, string senderName);

}

​

// Concrete colleague class (Regular User)

public class RegularUser : User

{

    public RegularUser(string name, IChatRoom chatRoom) : base(name, chatRoom)

    {

    }

​

    public override void Send(string message)

    {

        Console.WriteLine($"Regular User '{Name}' sends: {message}");

        chatRoom.SendMessage(message, Name);

    }

​

    public override void ReceiveMessage(string message, string senderName)

    {

        Console.WriteLine($"Regular User '{Name}' received from '{senderName}': {message}");

    }

}

​

// Concrete colleague class (Premium User)

public class PremiumUser : User

{

    public PremiumUser(string name, IChatRoom chatRoom) : base(name, chatRoom)

    {

    }

​

    public override void Send(string message)

    {

        Console.WriteLine($"Premium User '{Name}' sends: {message}");

        chatRoom.SendMessage(message, Name);

    }

​

    public override void ReceiveMessage(string message, string senderName)

    {

        Console.WriteLine($"Premium User '{Name}' received from '{senderName}': {message}");

    }

}

​

class Program

{

    static void Main()

    {

        IChatRoom chatRoom = new ChatRoom();

​

        // Create users and register them with the chat room (mediator)

        User john = new RegularUser("John", chatRoom);

        User anna = new PremiumUser("Anna", chatRoom);

        User mike = new RegularUser("Mike", chatRoom);

​

        // Send messages

        john.Send("Hello, everyone!");

        anna.Send("Hi, John!");

        mike.Send("Hey, guys!");

​

        /*

         * Sample Output:

         * Regular User 'John' sends: Hello, everyone!

         * Regular User 'Mike' received from 'John': Hello, everyone!

         * Premium User 'Anna' sends: Hi, John!

         * Regular User 'John' received from 'Anna': Hi, John!

         * Regular User 'Mike' sends: Hey, guys!

         * Regular User 'John' received from 'Mike': Hey, guys!

         * Premium User 'Anna' received from 'Mike': Hey, guys!

         */

    }

}

5. Mediator Pattern:

The Mediator pattern defines an object that encapsulates how a set of objects interact. It promotes loose coupling by keeping objects from referring to each other explicitly.

​

Example in React:

Suppose you have multiple components in your React application, and you want to create a mediator to manage communication between them.

​

import React, { useState } from 'react';

​

// Mediator

const Mediator = () => {

  const [state, setState] = useState('');

​

  const sendMessage = (message) => {

    setState(message);

  };

​

  return (

    <div>

      <p>Mediator State: {state}</p>

      <ComponentA sendMessage={sendMessage} />

      <ComponentB sendMessage={sendMessage} />

    </div>

  );

};

​

// Components

const ComponentA = ({ sendMessage }) => {

  const handleClick = () => {

    sendMessage('Hello from Component A');

  };

​

  return (

    <button onClick={handleClick}>Send Message from A</button>

  );

};

​

const ComponentB = ({ sendMessage }) => {

  const handleClick = () => {

    sendMessage('Hello from Component B');

  };

​

  return (

    <button onClick={handleClick}>Send Message from B</button>

  );

};

​

const MediatorPatternExample = () => {

  return (

    <div>

      <Mediator />

    </div>

  );

};

​

export default MediatorPatternExample;

​