import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;

/* Wire Format
 *                                1  1  1  1  1  1
 *  0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 * |     Magic       |Flags|       ZERO            |
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 * |                  Candidate ID                 |
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 * |                                               |
 * |         Vote Count (only in response)         |
 * |                                               |
 * |                                               |
 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 */
public class VoteMsgBinCoder implements VoteMsgCoder {

  // manifest constants for encoding
  public static final int MIN_WIRE_LENGTH = 4;
  public static final int MAX_WIRE_LENGTH = 16;
  public static final int MAGIC = 0x5400;
  public static final int MAGIC_MASK = 0xfc00;
  public static final int MAGIC_SHIFT = 8;
  public static final int RESPONSE_FLAG = 0x0200;
  public static final int INQUIRE_FLAG =  0x0100;

  public byte[] toWire(VoteMsg msg) throws IOException {
    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    DataOutputStream out = new DataOutputStream(byteStream); // converts ints

    short magicAndFlags = MAGIC;
    if (msg.isInquiry()) {
      magicAndFlags |= INQUIRE_FLAG;
    }
    if (msg.isResponse()) {
      magicAndFlags |= RESPONSE_FLAG;
    }
    out.writeShort(magicAndFlags);
    // We know the candidate ID will fit in a short: it's > 0 && < 1000 
    out.writeShort((short) msg.getCandidateID());
    if (msg.isResponse()) {
      out.writeLong(msg.getVoteCount());
    }
    out.flush();
    byte[] data = byteStream.toByteArray();
    return data;
  }

  public VoteMsg fromWire(byte[] input) throws IOException {
    // sanity checks
    if (input.length < MIN_WIRE_LENGTH) {
      throw new IOException("Runt message");
    }
    ByteArrayInputStream bs = new ByteArrayInputStream(input);
    DataInputStream in = new DataInputStream(bs);
    int magic = in.readShort();
    if ((magic & MAGIC_MASK) != MAGIC) {
      throw new IOException("Bad Magic #: " +
			    ((magic & MAGIC_MASK) >> MAGIC_SHIFT));
    }
    boolean resp = ((magic & RESPONSE_FLAG) != 0);
    boolean inq = ((magic & INQUIRE_FLAG) != 0);
    int candidateID = in.readShort();
    if (candidateID < 0 || candidateID > 1000) {
      throw new IOException("Bad candidate ID: " + candidateID);
    }
    long count = 0;
    if (resp) {
      count = in.readLong();
      if (count < 0) {
        throw new IOException("Bad vote count: " + count);
      }
    }
    // Ignore any extra bytes
    return new VoteMsg(resp, inq, candidateID, count);
  }
}