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

public class POP3Server
{
    
    static String SERVER_NAME = "localhost";
    static int POP_PORT = 110;
    
    POP3Server ()
    {
	try
	{
	    ServerSocket ss = new ServerSocket( POP3Server.POP_PORT );
	    System.out.println("Mail server is up and running on port " +  POP3Server.POP_PORT); 
	    while ( true ) 
	    {
		Socket theSocket = ss.accept();
		System.out.println("Connection accepted"); 
		(new POP3connection()).handleConnection(theSocket);
	    }
	}
	catch ( java.io.IOException ex )
	{
	    System.out.println("a - Exception: " +  ex);
	}
    }
    
    public static void main ( String[] args )
    {
	POP3Server mailServer = new POP3Server();
    }

    class POP3connection
    {
    
	List messageList = null;
	
	POP3connection ()
	{
	    createFakeMessage();
	}
	
	void createFakeMessage ()
	{
	    String message = new String ( 
	          "From: nobody@limbo.com\r\n" +
	          "Date: Wed, 18 Jul 2001 11:35:34 ED\r\n" +
		  "Subject: Test Message\r\n" +
		  "To: nobody@limbo.com\r\n" +
		  "\r\n" +
		  "Test\r\n" +
		  "\r\n");
	    
	    messageList = new Vector();
	    for (int i=0; i<5; i++)
	    {
		messageList.add(message);
	    }
	}
	
	void handleConnection ( Socket theSocket )
	{
	    boolean closeConnection = false;
	    boolean userAuthorised = true;
	    String params = "";
	    String request = "";
	    String user = "";
	    String password = "";
	    String data = "STAT\r\n";
	    
	    System.out.println("Connected to client");
	    
	    try 
	    {
	    
		OutputStream out = theSocket.getOutputStream();
		DataOutputStream dataSocketOut = new DataOutputStream(out);
	    
		InputStream in = theSocket.getInputStream();
		BufferedReader dataSocketIn = new BufferedReader(new InputStreamReader(in));
	    
		dataSocketOut.writeBytes("+OK POP3 server ready\r\n");
	    
		while ( !closeConnection )
		{
	    		
		    String result = "";
	
		    data = dataSocketIn.readLine();
		    data = data.trim();
		
		    if ( data.length() == 0 )
			continue;
		
		    int spaceIdx = data.indexOf(" ");
		    if ( spaceIdx > -1 )
		    {
			request = data.substring(0,spaceIdx);
			params = data.substring(spaceIdx);		    
		    }
		    else
		    {
			request = data;
			params = "";
		    }
				
		    System.out.println("REQUEST .... " + request);
		    System.out.println("PARAMS ..... " + params);

		    if ( request.equals("QUIT") )
		    {
			result = "+OK " + SERVER_NAME + " POP3 server signing off";
			closeConnection = true;
		    }
		    else if ( request.equals("APOP") )
		    {
			int lSpaceIdx = params.indexOf(" ");
			user = params.substring(0,lSpaceIdx);
			password = params.substring(lSpaceIdx);
			result = "+OK " + user + "'s maildrop has " + messageList.size() + "messages\r\n";
		    }
		    else if ( request.equals("USER") )
		    {
			user = params;
			result = "+OK\r\n";
		    }
		    else if ( request.equals("PASS") )
		    {
			password = params;
			// <-- Should do a password check here
			userAuthorised = true; 
			result = "+OK\r\n";
		    }				
		    else if ( request.equals("STAT") )
		    {
			if ( userAuthorised )
			{
			    List messagesSizes = new Vector();
			    int totalMessagesSize = 0;
			    result = "";
			    for ( int i=0; i < messageList.size(); i++ )
			    {
				int messageSize = ((String) messageList.get(i)).length();
				totalMessagesSize = totalMessagesSize + messageSize;
			    }		    
			    result = "+OK " + messageList.size() + " "
					    + totalMessagesSize + "\r\n";
			}
			else
			{
			    result = "-ERR must first login\r\n";		    
			}
		    }
		    else if ( request.equals("LIST") )
		    {
			if ( userAuthorised )
			{
			    List messagesSizes = new Vector();
			    int totalMessagesSize = 0;
			    result = "";
			    for ( int i=0; i < messageList.size(); i++ )
			    {
				int messageSize = ((String) messageList.get(i)).length();
				totalMessagesSize = totalMessagesSize + messageSize;
				result = result + i + " " + totalMessagesSize + "\r\n";
			    }
			    result += ".\r\n";		    
			    result = "+OK " + messageList.size() + " messages ("
					    + totalMessagesSize + ")\r\n"
					    + result;
			}
			else
			{
			    result = "-ERR must first login\r\n";
			}
		    }
		    else if ( request.equals("RETR") )
		    {
			if ( userAuthorised )
			{
			    int messageIdx = Integer.parseInt(params.trim());
			    result = "+OK " + ((String) messageList.get(messageIdx)).length() +" bytes\r\n";
			    result += (String) messageList.get(messageIdx) + "\r\n.\r\n";
			}
			else
			{
			    result = "-ERR must first login\r\n";
			}
		    }
		    else if ( request.equals("DELE") )
		    {
			if ( userAuthorised )
			    result = "+OK ignored command\r\n";
			else
			    result = "-ERR must first login\r\n";
		    }
		    else
		    {
			result = "-ERR unrecognised command\r\n";
		    }												
		
		    dataSocketOut.writeBytes(result);
		    System.out.println("RESULT ..... " + result);		
				
		}
	    
		theSocket.close();
	    
	    }
	    catch ( IOException ex )
	    {
		System.out.println("b - Exception : " + ex);
	    }
	}
    }
    
}