import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.util.Iterator;

public class TCPServerSelector {

  private static final int BUFSIZE = 256;  // Buffer size (bytes)
  private static final int TIMEOUT = 3000; // Wait timeout (milliseconds)

  public static void main(String[] args) throws IOException {

    if (args.length < 1) { // Test for correct # of args
      throw new IllegalArgumentException("Parameter(s): <Port> ...");
    }

    // Create a selector to multiplex listening sockets and connections
    Selector selector = Selector.open();

    // Create listening socket channel for each port and register selector
    for (String arg : args) {
      ServerSocketChannel listnChannel = ServerSocketChannel.open();
      listnChannel.socket().bind(new InetSocketAddress(Integer.parseInt(arg)));
      listnChannel.configureBlocking(false); // must be nonblocking to register
      // Register selector with channel. The returned key is ignored
      listnChannel.register(selector, SelectionKey.OP_ACCEPT);
    }

    // Create a handler that will implement the protocol
    TCPProtocol protocol = new EchoSelectorProtocol(BUFSIZE);

    while (true) { // Run forever, processing available I/O operations
      // Wait for some channel to be ready (or timeout)
      if (selector.select(TIMEOUT) == 0) { // returns # of ready chans
        System.out.print(".");
        continue;
      }

      // Get iterator on set of keys with I/O to process
      Iterator<SelectionKey> keyIter = selector.selectedKeys().iterator();
      while (keyIter.hasNext()) {
        SelectionKey key = keyIter.next(); // Key is bit mask
        // Server socket channel has pending connection requests?
        if (key.isAcceptable()) {
          protocol.handleAccept(key);
        }
        // Client socket channel has pending data?
        if (key.isReadable()) {
          protocol.handleRead(key);
        }
        // Client socket channel is available for writing and
        // key is valid (i.e., channel not closed)?
        if (key.isValid() && key.isWritable()) {
          protocol.handleWrite(key);
        }
        keyIter.remove(); // remove from set of selected keys
      }
    }
  }
}