/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.activemq.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.SocketTimeoutException;
import java.net.URI;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class SocketProxy {

    private static final transient Log LOG = LogFactory.getLog(SocketProxy.class);

    public static final int ACCEPT_TIMEOUT_MILLIS = 100;

    private URI proxyUrl;
    private URI target;

    private Acceptor acceptor;
    private ServerSocket serverSocket;
    
    private CountDownLatch closed = new CountDownLatch(1);

    public List<Bridge> connections = new LinkedList<Bridge>();

    private int listenPort = 0;

    private int receiveBufferSize = -1;

    private boolean pauseAtStart = false;

    private int acceptBacklog = 50;

    public SocketProxy() throws Exception {    
    }
    
    public SocketProxy(URI uri) throws Exception {
        this(0, uri);
    }

    public SocketProxy(int port, URI uri) throws Exception {
        listenPort = port;
        target = uri;
        open();
    }

    public void setReceiveBufferSize(int receiveBufferSize) {
        this.receiveBufferSize = receiveBufferSize;
    }
    
    public void setTarget(URI tcpBrokerUri) {
        target = tcpBrokerUri;
    }

    public void open() throws Exception {
        serverSocket = new ServerSocket();
        serverSocket.setReuseAddress(true);
        if (receiveBufferSize > 0) {
            serverSocket.setReceiveBufferSize(receiveBufferSize);
        }
        if (proxyUrl == null) {
            serverSocket.bind(new InetSocketAddress(listenPort), acceptBacklog);
            proxyUrl = urlFromSocket(target, serverSocket);
        } else {
            serverSocket.bind(new InetSocketAddress(proxyUrl.getPort()));
        }
        acceptor = new Acceptor(serverSocket, target);
        if (pauseAtStart) {
            acceptor.pause();
        }
        new Thread(null, acceptor, "SocketProxy-Acceptor-" + serverSocket.getLocalPort()).start();
        closed = new CountDownLatch(1);
    }

    public URI getUrl() {
        return proxyUrl;
    }

    /*
     * close all proxy connections and acceptor
     */
    public void close() {
        List<Bridge> connections;
        synchronized(this.connections) {
            connections = new ArrayList<Bridge>(this.connections);
        }            
        LOG.info("close, numConnectons=" + connections.size());
        for (Bridge con : connections) {
            closeConnection(con);
        }
        acceptor.close();
        closed.countDown();
    }

    /*
     * close all proxy receive connections, leaving acceptor
     * open
     */
    public void halfClose() {
        List<Bridge> connections;
        synchronized(this.connections) {
            connections = new ArrayList<Bridge>(this.connections);
        }            
        LOG.info("halfClose, numConnectons=" + connections.size());
        for (Bridge con : connections) {
            halfCloseConnection(con);
        }
    }

    public boolean waitUntilClosed(long timeoutSeconds) throws InterruptedException {
        return closed.await(timeoutSeconds, TimeUnit.SECONDS);
    }

    /*
     * called after a close to restart the acceptor on the same port
     */
    public void reopen() {
        LOG.info("reopen");
        try {
            open();
        } catch (Exception e) {
            LOG.debug("exception on reopen url:" + getUrl(), e);
        }
    }

    /*
     * pause accepting new connecitons and data transfer through existing proxy
     * connections. All sockets remain open
     */
    public void pause() {
        synchronized(connections) {
            LOG.info("pause, numConnectons=" + connections.size());
            acceptor.pause();
            for (Bridge con : connections) {
                con.pause();
            }
        }
    }

    /*
     * continue after pause
     */
    public void goOn() {
        synchronized(connections) {
            LOG.info("goOn, numConnectons=" + connections.size());
            for (Bridge con : connections) {
                con.goOn();
            }
        }
        acceptor.goOn();
    }

    private void closeConnection(Bridge c) {
        try {
            c.close();
        } catch (Exception e) {
            LOG.debug("exception on close of: " + c, e);
        }
    }

    private void halfCloseConnection(Bridge c) {
        try {
            c.halfClose();
        } catch (Exception e) {
            LOG.debug("exception on half close of: " + c, e);
        }
    }

    public boolean isPauseAtStart() {
        return pauseAtStart;
    }

    public void setPauseAtStart(boolean pauseAtStart) {
        this.pauseAtStart = pauseAtStart;
    }

    public int getAcceptBacklog() {
        return acceptBacklog;
    }

    public void setAcceptBacklog(int acceptBacklog) {
        this.acceptBacklog = acceptBacklog;
    }

    private URI urlFromSocket(URI uri, ServerSocket serverSocket) throws Exception {
        int listenPort = serverSocket.getLocalPort();

        return new URI(uri.getScheme(), uri.getUserInfo(), uri.getHost(), listenPort, uri.getPath(), uri.getQuery(), uri.getFragment());
    }

    public class Bridge {

        private Socket receiveSocket;
        private Socket sendSocket;
        private Pump requestThread;
        private Pump responseThread;

        public Bridge(Socket socket, URI target) throws Exception {
            receiveSocket = socket;
            sendSocket = new Socket();
            if (receiveBufferSize > 0) {
                sendSocket.setReceiveBufferSize(receiveBufferSize);
            }
            sendSocket.connect(new InetSocketAddress(target.getHost(), target.getPort()));
            linkWithThreads(receiveSocket, sendSocket);
            LOG.info("proxy connection " + sendSocket + ", receiveBufferSize=" + sendSocket.getReceiveBufferSize());
        }

        public void goOn() {
            responseThread.goOn();
            requestThread.goOn();
        }

        public void pause() {
            requestThread.pause();
            responseThread.pause();
        }

        public void close() throws Exception {
            synchronized(connections) {
                connections.remove(this);
            }
            receiveSocket.close();
            sendSocket.close();
        }

        public void halfClose() throws Exception {
            receiveSocket.close();
        }

        private void linkWithThreads(Socket source, Socket dest) {
            requestThread = new Pump(source, dest);
            requestThread.start();
            responseThread = new Pump(dest, source);
            responseThread.start();
        }

        public class Pump extends Thread {

            protected Socket src;
            private Socket destination;
            private AtomicReference<CountDownLatch> pause = new AtomicReference<CountDownLatch>();

            public Pump(Socket source, Socket dest) {
                super("SocketProxy-DataTransfer-" + source.getPort() + ":" + dest.getPort());
                src = source;
                destination = dest;
                pause.set(new CountDownLatch(0));
            }

            public void pause() {
                pause.set(new CountDownLatch(1));
            }

            public void goOn() {
                pause.get().countDown();
            }

            public void run() {
                byte[] buf = new byte[1024];
                try {
                    InputStream in = src.getInputStream();
                    OutputStream out = destination.getOutputStream();
                    while (true) {
                        int len = in.read(buf);
                        if (len == -1) {
                            LOG.debug("read eof from:" + src);
                            break;
                        }
                        pause.get().await();
                        out.write(buf, 0, len);
                    }
                } catch (Exception e) {
                    LOG.debug("read/write failed, reason: " + e.getLocalizedMessage());
                    try {
                        if (!receiveSocket.isClosed()) {
                            // for halfClose, on read/write failure if we close the
                            // remote end will see a close at the same time.
                            close();
                        }
                    } catch (Exception ignore) {
                    }
                }
            }
        }
    }

    public class Acceptor implements Runnable {

        private ServerSocket socket;
        private URI target;
        private AtomicReference<CountDownLatch> pause = new AtomicReference<CountDownLatch>();


        public Acceptor(ServerSocket serverSocket, URI uri) {
            socket = serverSocket;
            target = uri;
            pause.set(new CountDownLatch(0));
            try {
                socket.setSoTimeout(ACCEPT_TIMEOUT_MILLIS);
            } catch (SocketException e) {
                e.printStackTrace();
            }
        }

        public void pause() {
            pause.set(new CountDownLatch(1));
        }
        
        public void goOn() {
            pause.get().countDown();
        }

        public void run() {
            try {
                while(!socket.isClosed()) {
                    pause.get().await();
                    try {
                        Socket source = socket.accept();
                        pause.get().await();
                        if (receiveBufferSize > 0) {
                            source.setReceiveBufferSize(receiveBufferSize);
                        }
                        LOG.info("accepted " + source + ", receiveBufferSize:" + source.getReceiveBufferSize());
                        synchronized(connections) {
                            connections.add(new Bridge(source, target));
                        }
                    } catch (SocketTimeoutException expected) {
                    }
                }
            } catch (Exception e) {
                LOG.debug("acceptor: finished for reason: " + e.getLocalizedMessage());
            }
        }
        
        public void close() {
            try {
                socket.close();
                closed.countDown();
                goOn();
            } catch (IOException ignored) {
            }
        }
    }

}

