package upem.net.tcp.nonblocking;

import java.io.Closeable;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Set;

public class ServerEcho {

    private final ServerSocketChannel serverSocketChannel;
    private final Selector selector;
    private final Set<SelectionKey> selectedKeys;

    public ServerEcho(int port) throws IOException {
        serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(port));
        selector = Selector.open();
        selectedKeys = selector.selectedKeys();
    }

    public void launch() throws IOException {
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        while (!Thread.interrupted()) {
            selector.select();
            processSelectedKeys();
            selectedKeys.clear();
        }
    }


    private void processSelectedKeys() throws IOException {
        for (SelectionKey key : selectedKeys) {
            if (key.isValid() && key.isAcceptable()) {
                doAccept(key);
            }
            try {
                if (key.isValid() && key.isWritable()) {
                 doWrite(key);
                }
                if (key.isValid() && key.isReadable()) {
                 doRead(key);
                }
            } catch (IOException e) {
                closeConnection(key);
            }
        }
    }

    private void updateKeyInterestOps(SelectionKey key){
        EchoAttachment attachment = (EchoAttachment) key.attachment();
        ByteBuffer bb = attachment.getBuffer();
        int interestOps=0;
        if (bb.hasRemaining() && !attachment.isInputClosed()){
            interestOps=interestOps|SelectionKey.OP_READ;
        }
        if (bb.position()!=0) {
            interestOps=interestOps|SelectionKey.OP_WRITE;
        }
        key.interestOps(interestOps);
        if (interestOps==0) {
            closeConnection(key);
        }
    }

    private void doRead(SelectionKey key) throws IOException {
        SocketChannel sc = (SocketChannel) key.channel();
        EchoAttachment attachment = (EchoAttachment) key.attachment();
        ByteBuffer bb = attachment.getBuffer();
        if (sc.read(bb)==-1) {
            attachment.setInputClosed(true);
        }
        updateKeyInterestOps(key);
    }

    private void doWrite(SelectionKey key) throws IOException {
        SocketChannel sc = (SocketChannel) key.channel();
        EchoAttachment attachment = (EchoAttachment) key.attachment();
        ByteBuffer bb = attachment.getBuffer();
        bb.flip();
        sc.write(bb);
        bb.compact();
        updateKeyInterestOps(key);
    }

    private void closeConnection(SelectionKey key){
        SocketChannel sc = (SocketChannel) key.channel();
        silentlyClose(sc);
        key.attach(null);
    }

    private void silentlyClose(Closeable sc) {
        if (sc!=null) {
            try {
                sc.close();
            } catch (Exception e) {
                // Ignore exceptions
            }
        }
    }

    private void doAccept(SelectionKey key) throws IOException {
        SocketChannel sc = serverSocketChannel.accept();
        if (sc==null) return; // In case, the selector gave a bad hint
        sc.configureBlocking(false);
        sc.register(selector,SelectionKey.OP_READ, new EchoAttachment(8));
    }

    public static void main(String[] args) throws NumberFormatException, IOException {
        new ServerEcho(Integer.parseInt(args[0])).launch();

    }
}