package dcj.util.message;

import java.util.Vector;
import java.io.*;

/**
 * Source code from "Java Distributed Computing", by Jim Farley.
 *
 * Class: MessageHandler
 * Example: 6-10
 * Description: The final version of the basic message handler.
 */

public class MessageHandler implements Runnable
{
  // A global MessageHandler, for applications where one central
  // handler is used.
  public static MessageHandler current = null;

  InputStream msgIn;
  OutputStream msgOut;
  Vector msgPrototypes;

  public MessageHandler() {}
  public MessageHandler(InputStream in, OutputStream out) {
    setStreams(in, out);
  }

  public void setStreams(InputStream in, OutputStream out) {
    msgIn = in;
    msgOut = out;
  }

  public void addMessageType(Message prototype) {
    msgPrototypes.addElement(prototype);
  }

  public Message readMsg() throws IOException {
    Message msg = null;
    DataInputStream din = new DataInputStream(msgIn);

    String msgId = din.readUTF();
    msg = buildMessage(msgId);
    if (msg != null && msg.readArgs(msgIn)) {
      return msg;
    }
    else {
      return null;
    }
  }

  public void sendMsg(Message msg) throws IOException {
    boolean success = true;
    DataOutputStream dout = new DataOutputStream(msgOut);

    dout.writeUTF(msg.messageID());
    msg.writeArgs(msgOut);
  }

  public void run() {
    try {
      while (true) {
        Message msg = readMsg();
        if (msg != null) {
          msg.Do();
        }
      }
    }
    // Treat an IOException as a termination of the message
    // exchange, and let this message-processing thread die.
    catch (IOException e) {}
  }

  protected Message buildMessage(String msgId) {
    Message msg = null;
    int numMTypes = msgPrototypes.size();
    for (int i = 0; i < numMTypes; i++) {
      Message m = (Message)msgPrototypes.elementAt(i);
      if (m.handles(msgId)) {
        msg = m.newCopy();
        break;
      }
    }
    return msg;
  }
}