import java.io.IOException;

import java.net.ServerSocket;

import java.net.Socket;

import java.util.HashSet;

import java.util.Set;

/*

This is the chat server program.

*/

public class ChatServer {

private int port;

private Set<String> userNames = new HashSet<>();

private Set<UserThread> userThreads = new HashSet<>();

public ChatServer(int port) {

this.port = port;

}

public void execute() {

try (ServerSocket serverSocket = new ServerSocket(port)) {

System.out.println("Chat Server is listening on port " + port);

while(true) {

Socket socket = serverSocket.accept();

System.out.println("New user connected");

UserThread newUser = new UserThread(socket, this);

userThreads.add(newUser);

newUser.start();

}

} catch (IOException ex) {

System.out.println("Error in the server: " + ex.getMessage());

ex.printStackTrace();

}

}

public static void main(String[] args) {

if (args.length < 1) {

System.out.println("Syntax: java ChatServer <port-number>");

System.exit(0);

}

int port = Integer.parseInt(args[0]);

ChatServer server = new ChatServer(port);

server.execute();

}

/*

Delivers a message from one user to others (broadcasting)

*/

void broadcast (String message, UserThread excludeUser) {

for (UserThread aUser : userThreads

) {

if (!aUser.equals(excludeUser)) {

aUser.sendMessage(message); // sends message back to the client

}

}

}

/*

Stores username of the newly connected client.

*/

void addUserName(String userName) {

userNames.add(userName);

}

/*

When a client is disconnected, removes the associated username and userThread

*/

void removeUser (String userName, UserThread aUser) {

boolean removed = userNames.remove(userName);

if (removed) {

userThreads.remove(aUser);

System.out.println("The user " + userName + " quit.");

}

}

Set<String> getUserNames() {

return this.userNames;

}

/*

Returns true if there are others users connected (not count the currently

connected user)

*/

boolean hasUsers() {

return !this.userNames.isEmpty();

}

}