/*

 * Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

import java.io.Closeable;

import java.io.IOException;

import java.io.UncheckedIOException;

import java.net.InetSocketAddress;

import java.net.URI;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.channels.ClosedByInterruptException;

import java.nio.channels.ServerSocketChannel;

import java.nio.channels.SocketChannel;

import java.nio.charset.CharacterCodingException;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.util.Arrays;

import java.util.Base64;

import java.util.HashMap;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.List;

import java.util.Map;

import java.util.concurrent.atomic.AtomicBoolean;

import java.util.function.Function;

import java.util.regex.Pattern;

import java.util.stream.Collectors;

import static java.lang.String.format;

import static java.lang.System.Logger.Level.ERROR;

import static java.lang.System.Logger.Level.INFO;

import static java.lang.System.Logger.Level.TRACE;

import static java.nio.charset.StandardCharsets.ISO_8859_1;

import static java.util.Arrays.asList;

import static java.util.Objects.requireNonNull;

/**

 * Dummy WebSocket Server.

 *

 * Performs simpler version of the WebSocket Opening Handshake over HTTP (i.e.

 * no proxying, cookies, etc.) Supports sequential connections, one at a time,

 * i.e. in order for a client to connect to the server the previous client must

 * disconnect first.

 *

 * Expected client request:

 *

 *     GET /chat HTTP/1.1

 *     Host: server.example.com

 *     Upgrade: websocket

 *     Connection: Upgrade

 *     Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==

 *     Origin: http://example.com

 *     Sec-WebSocket-Protocol: chat, superchat

 *     Sec-WebSocket-Version: 13

 *

 * This server response:

 *

 *     HTTP/1.1 101 Switching Protocols

 *     Upgrade: websocket

 *     Connection: Upgrade

 *     Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=

 *     Sec-WebSocket-Protocol: chat

 */

public final class DummyWebSocketServer implements Closeable {

    private final static System.Logger log = System.getLogger(DummyWebSocketServer.class.getName());

    private final AtomicBoolean started = new AtomicBoolean();

    private final Thread thread;

    private volatile ServerSocketChannel ssc;

    private volatile InetSocketAddress address;

    public DummyWebSocketServer() {

        this(defaultMapping());

    }

    public DummyWebSocketServer(Function<List<String>, List<String>> mapping) {

        requireNonNull(mapping);

        thread = new Thread(() -> {

            try {

                while (!Thread.currentThread().isInterrupted()) {

                    log.log(INFO, "Accepting next connection at: " + ssc);

                    SocketChannel channel = ssc.accept();

                    log.log(INFO, "Accepted: " + channel);

                    try {

                        channel.configureBlocking(true);

                        StringBuilder request = new StringBuilder();

                        if (!readRequest(channel, request)) {

                            throw new IOException("Bad request");

                        }

                        List<String> strings = asList(request.toString().split("\r\n"));

                        List<String> response = mapping.apply(strings);

                        writeResponse(channel, response);

                        // Read until the thread is interrupted or an error occurred

                        // or the input is shutdown

                        ByteBuffer b = ByteBuffer.allocate(1024);

                        while (channel.read(b) != -1) {

                            b.clear();

                        }

                    } catch (IOException e) {

                        log.log(TRACE, () -> "Error in connection: " + channel, e);

                    } finally {

                        log.log(INFO, "Closed: " + channel);

                        close(channel);

                    }

                }

            } catch (ClosedByInterruptException ignored) {

            } catch (IOException e) {

                log.log(ERROR, e);

            } finally {

                close(ssc);

                log.log(INFO, "Stopped at: " + getURI());

            }

        });

        thread.setName("DummyWebSocketServer");

        thread.setDaemon(false);

    }

    public void open() throws IOException {

        log.log(INFO, "Starting");

        if (!started.compareAndSet(false, true)) {

            throw new IllegalStateException("Already started");

        }

        ssc = ServerSocketChannel.open();

        try {

            ssc.configureBlocking(true);

            ssc.bind(new InetSocketAddress("localhost", 0));

            address = (InetSocketAddress) ssc.getLocalAddress();

            thread.start();

        } catch (IOException e) {

            close(ssc);

        }

        log.log(INFO, "Started at: " + getURI());

    }

    @Override

    public void close() {

        log.log(INFO, "Stopping: " + getURI());

        thread.interrupt();

    }

    URI getURI() {

        if (!started.get()) {

            throw new IllegalStateException("Not yet started");

        }

        return URI.create("ws://" + address.getHostName() + ":" + address.getPort());

    }

    private boolean readRequest(SocketChannel channel, StringBuilder request)

            throws IOException

    {

        ByteBuffer buffer = ByteBuffer.allocate(512);

        int num = channel.read(buffer);

        if (num == -1) {

            return false;

        }

        CharBuffer decoded;

        buffer.flip();

        try {

            decoded = ISO_8859_1.newDecoder().decode(buffer);

        } catch (CharacterCodingException e) {

            throw new UncheckedIOException(e);

        }

        request.append(decoded);

        return Pattern.compile("\r\n\r\n").matcher(request).find();

    }

    private void writeResponse(SocketChannel channel, List<String> response)

            throws IOException

    {

        String s = response.stream().collect(Collectors.joining("\r\n"))

                + "\r\n\r\n";

        ByteBuffer encoded;

        try {

            encoded = ISO_8859_1.newEncoder().encode(CharBuffer.wrap(s));

        } catch (CharacterCodingException e) {

            throw new UncheckedIOException(e);

        }

        while (encoded.hasRemaining()) {

            channel.write(encoded);

        }

    }

    private static Function<List<String>, List<String>> defaultMapping() {

        return request -> {

            List<String> response = new LinkedList<>();

            Iterator<String> iterator = request.iterator();

            if (!iterator.hasNext()) {

                throw new IllegalStateException("The request is empty");

            }

            if (!"GET / HTTP/1.1".equals(iterator.next())) {

                throw new IllegalStateException

                        ("Unexpected status line: " + request.get(0));

            }

            response.add("HTTP/1.1 101 Switching Protocols");

            Map<String, String> requestHeaders = new HashMap<>();

            while (iterator.hasNext()) {

                String header = iterator.next();

                String[] split = header.split(": ");

                if (split.length != 2) {

                    throw new IllegalStateException

                            ("Unexpected header: " + header

                                     + ", split=" + Arrays.toString(split));

                }

                if (requestHeaders.put(split[0], split[1]) != null) {

                    throw new IllegalStateException

                            ("Duplicating headers: " + Arrays.toString(split));

                }

            }

            if (requestHeaders.containsKey("Sec-WebSocket-Protocol")) {

                throw new IllegalStateException("Subprotocols are not expected");

            }

            if (requestHeaders.containsKey("Sec-WebSocket-Extensions")) {

                throw new IllegalStateException("Extensions are not expected");

            }

            expectHeader(requestHeaders, "Connection", "Upgrade");

            response.add("Connection: Upgrade");

            expectHeader(requestHeaders, "Upgrade", "websocket");

            response.add("Upgrade: websocket");

            expectHeader(requestHeaders, "Sec-WebSocket-Version", "13");

            String key = requestHeaders.get("Sec-WebSocket-Key");

            if (key == null) {

                throw new IllegalStateException("Sec-WebSocket-Key is missing");

            }

            MessageDigest sha1 = null;

            try {

                sha1 = MessageDigest.getInstance("SHA-1");

            } catch (NoSuchAlgorithmException e) {

                throw new InternalError(e);

            }

            String x = key + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";

            sha1.update(x.getBytes(ISO_8859_1));

            String v = Base64.getEncoder().encodeToString(sha1.digest());

            response.add("Sec-WebSocket-Accept: " + v);

            return response;

        };

    }

    protected static String expectHeader(Map<String, String> headers,

                                         String name,

                                         String value) {

        String v = headers.get(name);

        if (!value.equals(v)) {

            throw new IllegalStateException(

                    format("Expected '%s: %s', actual: '%s: %s'",

                           name, value, name, v)

            );

        }

        return v;

    }

    private static void close(AutoCloseable... acs) {

        for (AutoCloseable ac : acs) {

            try {

                ac.close();

            } catch (Exception ignored) { }

        }

    }

}