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

/**
 * MailStat is used to check if mail is waiting at the given POP3 post
 * office.
 *
 * @author  Thornton Rose
 * @version 1.0
 */
public class MailStat
{
   private static final int POP3_PORT = 110;

   public static void main(String[] args) {
      String            host;
      InetAddress       hostAddress;
      String            username;
      String            password;
      Socket            mailSocket;
      BufferedReader    socketInput;
      DataOutputStream  socketOutput;
      
      // Check args.

      if (args.length < 3) {
         System.out.println("Usage: MailStat [host] [username] [password]");
         System.out.println("");
         System.out.println("Parameters:");
         System.out.println("   host     = Name or IP address of mail host.");
         System.out.println("   username = Account on mail host.");
         System.out.println("   password = Password on mail host.");
      }
      else {
         // Get host, username, and password.

         host = args[0];
         username = args[1];
         password = args[2];

         try {
            // Open the connection to the host.

            hostAddress = InetAddress.getByName(host);
            System.out.println("Opening connection to " + hostAddress + "...");
            mailSocket = new Socket(host, POP3_PORT);

            try {
               // Get references to the input and output streams.

               socketInput = new BufferedReader(
                  new InputStreamReader(mailSocket.getInputStream()) );
               socketOutput = new DataOutputStream(mailSocket.getOutputStream());

               // Get the initial reply from the server.

               readReply(socketInput);

               // Authenticate: send username and password.

               sendCommand(socketOutput, "USER " + username);
               readReply(socketInput);
               sendCommand(socketOutput, "PASS " + password);
               readReply(socketInput);

               // Get the status.

               sendCommand(socketOutput, "STAT");
               readReply(socketInput);

               // End the session.

               sendCommand(socketOutput, "QUIT");
               readReply(socketInput);

            } finally {
               mailSocket.close();
            }
         }
         catch(Exception theException) {
            System.out.println(theException);
         }
      }

      System.exit(0);
   }

   /**
    * sendCommand() sends an POP3 command to the POP3 server. An
    * POP3 command is a string that looks like:
    * <pre>
    * [keyword] [data][CR][LF]
    * </pre>
    *
    * <p>Example: <pre>USER trose</pre>
    *
    * @param out          The output stream to which to write the command.
    * @param command      The command to write.
    *
    * @exception IOException No special handling is done; the exception is
    *    passed back up the call chain.
    */
   private static void sendCommand(DataOutputStream out, String command) 
      throws IOException {
      
      System.out.println(command);
      out.writeBytes(command + "\r\n");
   }

   /**
    * readReply() reads the reply from the POP3 server.
    *
    * @param reader       The input reader from which to read the reply.
    *
    */
   /* @exception IOException If an IOException occurs because of an error
    *    with socket IO, no special handling is done, and the exception is
    *    passed back up the call chain. If the reply from the server
    *    indicates that an error occurred, an IOException containing
    *    "POP3: " + the reply is thrown.
    */
   private static String readReply(BufferedReader reader)
      throws IOException, Exception {
      
      String reply;
      
      reply = reader.readLine();
      System.out.println(reply);

      if (reply.substring(0, 4).equalsIgnoreCase("-ERR")) {
         throw (new Exception("POP3: " + reply));
      }

      return reply;
   }
}