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

class Client
{
  public static void main(String args[]) throws Exception
  {
    // messages to transmit
    String[] message = {"message 1", "message 2", "message 3", "message 4",
              "message 5", "message 6", "message 7", "message 8"};

    // open an UDP socket (for input/output)
    DatagramSocket clientSocket = new DatagramSocket();
    InetAddress IPAddress = InetAddress.getByName("localhost");
    int messageInd = 0;             // init message index
    int state = 0;              // FSM state

    while(true)                 // TX FSM
    {
      if (messageInd == message.length) break;  // loop over messages
      switch (state)
      {
        // compose packet and transmit it
        case 0:                 // compose packet and TX it
          Packet p = new Packet(message[messageInd], 0); // create packet
      short distortion = (short) Math.ceil(Math.random()*2);
          p.crc ^= distortion;
      byte[] pkt = Packet.serialize(p);     // and serialize it
          DatagramPacket sendPacket =           // add packet fields
             new DatagramPacket(pkt, pkt.length, IPAddress, 9876);
          clientSocket.send(sendPacket);        // send packet to server
          state = 1;                            // transfer to state 1
          break;

        // wait for ACK for packet #0
        case 1:
          byte[] receiveData = new byte[1000];  // buffer for ACK packet
          DatagramPacket receivePacket =
             new DatagramPacket(receiveData, receiveData.length);
          clientSocket.receive(receivePacket);  // wait for ACK
          p = Packet.deserialize(receivePacket.getData());
      short ourCRC = Packet.computeCRC(p.payload); // real packet CRC
      if ((ourCRC != p.crc) || p.pktNo != 0)
      {
        p = new Packet(message[messageInd], 0); // create packet
            distortion = (short) Math.ceil(Math.random()*2);
            p.crc ^= distortion;
            pkt = Packet.serialize(p);          // and serialize it
            sendPacket =                        // add packet fields
               new DatagramPacket(pkt, pkt.length, IPAddress, 9876);
            clientSocket.send(sendPacket);      // send packet to server
          }
          else
          {
            messageInd++;           // prepare to send next msg
            state = 2;              // update state
          }
          break;

        case 2:
          p = new Packet(message[messageInd], 1); // create packet
          distortion = (short) Math.ceil(Math.random()*2);
          p.crc ^= distortion;
          pkt = Packet.serialize(p);            // and serialize it
          sendPacket =                          // add packet fields
             new DatagramPacket(pkt, pkt.length, IPAddress, 9876);
          clientSocket.send(sendPacket);        // send packet to server
          state = 3;                            // transfer to state 3
          break;

        case 3:
          receiveData = new byte[1000];         // buffer for ACK packet
          receivePacket =
             new DatagramPacket(receiveData, receiveData.length);
          clientSocket.receive(receivePacket);  // wait for ACK
          p = Packet.deserialize(receivePacket.getData());
          ourCRC = Packet.computeCRC(p.payload); // real packet CRC
          if ((ourCRC != p.crc) || p.pktNo != 1)
          {
            p = new Packet(message[messageInd], 1); // create packet
            distortion = (short) Math.ceil(Math.random()*2);
            p.crc ^= distortion;
            pkt = Packet.serialize(p);          // and serialize it
            sendPacket =                        // add packet fields
               new DatagramPacket(pkt, pkt.length, IPAddress, 9876);
            clientSocket.send(sendPacket);      // send packet to server
          }
          else
          {
            messageInd++;                       // prepare to send next msg
            state = 0;                          // update state
          }
          break;
      }
    }

    clientSocket.close();
  }

}