import java.util.*;
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

/** Implementation of Server */
public class ServerImpl
        extends UnicastRemoteObject
        implements Server
{
	Hashtable connections = new Hashtable();

	public ServerImpl() throws RemoteException {
		}

        public void notifyWhoChanged() {
		// OK. We had to fix a little problem here.
		// We need to tell all connections that a new user has logged on
		// However, the user logging on might not be fully established,
		// and be unable to accept the message that whoChanged until
		// such time as the log-on is complete.
		// We can fix this either Server side or Client Side.
		// The Server side fix is to run this in a seperate thread,
		// so that if it blocks, we won't delay the return from logon
		// (which could create deadlock)
		(new Thread() {
		  public void run() {
                    Hashtable sendTo;
                    synchronized (connections) {
                      sendTo = (Hashtable)connections.clone();
                    }
                for (Enumeration e = sendTo.keys(); e.hasMoreElements(); )  {
                  String who = (String)e.nextElement();
                  Client c = (Client)sendTo.get(who);
                  try { c.whoChanged(); }
		  catch (RemoteException err) {
                        System.out.println("Dropping " + who + " due to remote error");
                        connections.remove(who);
                        }
                     }
                   }
	        }).start();
		}

	public Connection logon(String name, Client c) throws java.rmi.RemoteException {
		Connection conn;
		synchronized (connections) {
		  if (name.equals("Server") || connections.get(name) != null) {
			c.speak("Server","Sorry, but that name is already in use");
			return null;
			}
		  conn = new ConnectionImpl(name, c, this, connections);
		  connections.put(name,c);
		  }
		c.speak("Server","Welcome");
		notifyWhoChanged();
		return conn;
		}
		
        public static void main(String args[])
        {

                try {
                        ServerImpl obj = new ServerImpl();
                        Naming.rebind("//savoir.cs.umd.edu/ChatServer", obj);
			// Create and install a security manager
			// System.setSecurityManager(new RMISecurityManager());
                        System.out.println("ChatServer bound in registry");
                } catch (Exception e) {
                        System.out.println("ChatServerImpl err: " + e.getMessage());
                        e.printStackTrace();
                }
        }
}