package altbit;

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

/** The Channel class is used to simulate the channels between
  * a Sender and a Receiver in the alternating bit protocol.
  * The "machine" that is sending messages first connects to the
  * channel.  Then the channel connects to the target "machine".
  */
public class Channel {

  public static final int CHANNEL_PORT = 4444;

  public static final int NORMAL = 0;
  public static final int LOSEODD = 1;  
  public static final int LOSEEVEN = 2;

  private int state = 1;
  private int channel_port;
  private int behavior = NORMAL;
  // Sockets to receive connection
  private ServerSocket ss;
  private Socket s_in;
  // Socket to make connection
  private Socket s_out;
  // Object InputStreams to read and write messages to Sender and Receiver
  private ObjectInputStream in;
  private ObjectOutputStream out;

  /** Creates a Channel listening to the default channel port number.
    */
  public Channel() { channel_port = CHANNEL_PORT; }

  /** Creates a Channel listening to the passed-in port number.
    */
  public Channel(int port) { channel_port = port; }

  /** Listens and connects the "machine" that is sending messages
    * across this channel.
    */
  public void accept() {
    try {
      ss = new ServerSocket(channel_port);
      s_in = null;
      s_in = ss.accept();
      in = new ObjectInputStream(s_in.getInputStream());
    }
    catch (IOException e) {
      System.out.println("Could not receive connection.");
      System.out.println(e);
      System.exit(0);
    }
  }

  /** Connects the Channel object to the target "machine" listening at the
    * specified location.
    */
  public boolean connect(String host, int port) {
    s_out = null;
    try {
      s_out = new Socket(host, port);
      out = new ObjectOutputStream(s_out.getOutputStream());
    }
    catch (UnknownHostException e) {
      System.out.println("Host: " + host + " unknown or unavailable.");
      return false;
    }
    catch (IOException e) {
      System.out.println("Error occurred trying to connect to " +
                         host + " at port " + port + ".");
      System.out.println(e);
      System.exit(0);
    }

    // If it works ...
    System.out.println("Channel up and running!");
    return true;
  }

  /** Simulates a channel with errored behavior.
    */
  private void errorBehavior() {
    Object o = null;
    while (true) {
      try {
        switch (state) {
        case 1:
          o = in.readObject();
          state = 2;
          break;
        case 2:
          o = in.readObject();
          state = 3;
          break;
        case 3:
          out.writeObject(o);
          state = 1;
          break;
        }
      }
      catch (IOException e) { ; }
      catch (ClassNotFoundException e) { ; }
    }
  }

  public static void main(String args[]) {

    Channel c = null;

    if (args.length == 0) {
      c = new Channel();
    }
    else {
      String s = args[0];
      int c_port;
      try {
        c_port = Integer.parseInt(s);
      }
      catch (NumberFormatException e) {
        c_port = CHANNEL_PORT;
      }
      c = new Channel(c_port);
    }

    // set channel 1 and 2 behaviors based off command-line arguments
    for (int i = 1; i < args.length; i++) {
      if (args[i].equals("-o")) c.behavior = LOSEODD;
      else if (args[i].equals("-e")) c.behavior = LOSEEVEN;
      else {
        System.out.println("Usage: java Channel <port> -[oe]");
        System.out.println("       option o: channel lose every odd numbered message");
        System.out.println("       option e: channel lose every even numbered message");
      }
    }

    // Receive connection from sending process
    System.out.println("Channel listening on port " + c.channel_port);
    System.out.flush();
    c.accept();
    System.out.println("Connection received.");

    // Make connection to target process
    boolean done = false;
    String hostname;
    int port;
    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
    while (!done) {
      System.out.println("Enter target Hostname and port number:");
      System.out.flush();
      String s;
      try {
        s = input.readLine();
      }
      catch (IOException e) { continue; }
      StringTokenizer st = new StringTokenizer(s);
      if (st.countTokens() != 2) {
        System.out.println("You must enter a hostname and port number.\n");
        continue;
      }
      hostname = st.nextToken();
      String p = st.nextToken();
      try {
        port = Integer.parseInt(p);
      }
      catch (NumberFormatException e) {
        System.out.println("You must enter a valid port number.\n");
        continue;
      }
      done = c.connect(hostname, port);
    }

    if (c.behavior == LOSEODD) {
      c.state = 1;
      c.errorBehavior();
    }
    else if (c.behavior == LOSEEVEN) {
      c.state = 2;
      c.errorBehavior();
    }
    else {
      Message m = null;
      while (true) {
        try {
          m = (Message) c.in.readObject();
        }
        catch (IOException e) { continue; }
        catch (ClassNotFoundException e) { continue; }
        try {
          c.out.writeObject(m);
        }
        catch (IOException e) { ; }
      }
    }
  }
}