import java.io.*;
import java.net.*;
import java.util.*;

public class Server
{
    public static final int PORT = 50007;
    //set of unique clients names
    private static Set<String> names = new HashSet<>();
    //set of unique client senders
    private static Set<PrintWriter> senders = new HashSet<>();

    public static void main(String args[]) throws IOException
    {
        //create server socket
        ServerSocket server = new ServerSocket(PORT);
        Socket client;

        System.out.println("Waiting for connection to:" + server);
        while(true)
        {
            //waiting for client connection
            client = server.accept();
            //create new thread for handling new client
            new ClientHandler(client).start();
        }
    }
    private static class ClientHandler extends Thread
    {
        private String name; //client name
        private Socket client; //client socket

        private BufferedReader clientReceiver; //receiver
        private PrintWriter clientSender; //sender
        public ClientHandler(Socket client)
        {
            this.client = client;
        }
        public void run()
        {
            try
            {
                //create receiver stream
                this.clientReceiver = new BufferedReader(new InputStreamReader(this.client.getInputStream()));
                //create sender stream
                this.clientSender = new PrintWriter(this.client.getOutputStream());

                //ask new client for unique name
                this.clientSender.println("Your name?");
                this.clientSender.flush();
                while(true)
                {
                    //if client buffer is not empty --> asign name
                    if(this.clientReceiver.ready())
                    {
                        this.name = this.clientReceiver.readLine();
                        synchronized(names)
                        {
                            //synchronus access to client's names
                            //if unique name is not empty and not equals blank chars --> accept name
                            if(!this.name.trim().isEmpty() && !names.contains(name))
                            {
                                //add name to known names
                                names.add(this.name);

                                //print welcome message
                                this.clientSender.println("Welcome " + this.name + "!");
                                this.clientSender.flush();
                                break;
                            }
                            else
                            {
                                //if name in use or is empty --> ask for nem name
                                this.clientSender.println("Name: " + this.name + "is already in use!\n" + "Your name?");
                                this.clientSender.flush();
                            }
                        }

                    }
                }
                //send message to all known clients, that new client has joined chat
                for (PrintWriter sender : senders)
                {
                    sender.println(this.name + "has joined");
                    sender.flush();
                }
                //add client to list of known clients
                senders.add(this.clientSender);

                //begin broadcasting
                String message = "";
                boolean exit = false;
                while(!exit)
                {
                    //if client buffer is not empty --> broadcast message
                    if(this.clientReceiver.ready())
                    {
                        message = this.clientReceiver.readLine();
                        //format message
                        if(!message.equalsIgnoreCase("end"))
                        {
                            message = "<" + this.name + ">:" + message;
                        }
                        else
                        {
                            //if message equals "end" --> close connection
                            message = this.name + "has left";
                            exit = true;
                        }
                        //send message to know hosts
                        for(PrintWriter sender : senders)
                        {
                            if(sender != this.clientSender)
                            {
                                sender.println(message);
                                sender.flush();
                            }
                        }
                    }
                }
                //remove client from known hosts
                senders.remove(this.clientSender);
                names.remove(this.name);
                //close streams
                this.clientReceiver.close();
                this.clientSender.close();
                this.client.close();
            }
            catch(IOException e)
            {
                System.out.println(e);
            }
        }
    }
}