import java.nio.channels.SelectionKey;
import java.nio.channels.SocketChannel;
import java.nio.channels.ServerSocketChannel;
import java.nio.ByteBuffer;
import java.io.IOException;

public class EchoSelectorProtocol implements TCPProtocol {

  private int bufSize; // Size of I/O buffer

  public EchoSelectorProtocol(int bufSize) {
    this.bufSize = bufSize;
  }

  public void handleAccept(SelectionKey key) throws IOException {
    SocketChannel clntChan = ((ServerSocketChannel) key.channel()).accept();
    clntChan.configureBlocking(false); // Must be nonblocking to register
    // Register the selector with new channel for read and attach byte buffer
    clntChan.register(key.selector(), SelectionKey.OP_READ, ByteBuffer
        .allocate(bufSize));
  }

  public void handleRead(SelectionKey key) throws IOException {
    // Client socket channel has pending data
    SocketChannel clntChan = (SocketChannel) key.channel();
    ByteBuffer buf = (ByteBuffer) key.attachment();
    long bytesRead = clntChan.read(buf);
    if (bytesRead == -1) { // Did the other end close?
      clntChan.close();
    } else if (bytesRead > 0) {
      // Indicate via key that reading/writing are both of interest now.
      key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE);
    }
  }

  public void handleWrite(SelectionKey key) throws IOException {
    /*
     * Channel is available for writing, and key is valid (i.e., client channel
     * not closed).
     */
    // Retrieve data read earlier
    ByteBuffer buf = (ByteBuffer) key.attachment();
    buf.flip(); // Prepare buffer for writing
    SocketChannel clntChan = (SocketChannel) key.channel();
    clntChan.write(buf);
    if (!buf.hasRemaining()) { // Buffer completely written?
      // Nothing left, so no longer interested in writes
      key.interestOps(SelectionKey.OP_READ);
    }
    buf.compact(); // Make room for more data to be read in
  }

}