/*

 * Copyright (c) 2016, 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.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.ServerSocketChannel;

import java.nio.channels.SocketChannel;

import java.nio.charset.CharacterCodingException;

import java.nio.charset.StandardCharsets;

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.CompletableFuture;

import java.util.function.Function;

import java.util.regex.Pattern;

import java.util.stream.Collectors;

import static java.lang.String.format;

import static java.util.Objects.requireNonNull;

//

// Performs a simple opening handshake and yields the channel.

//

// 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

//

//

// Server Response:

//

//    HTTP/1.1 101 Switching Protocols

//    Upgrade: websocket

//    Connection: Upgrade

//    Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=

//    Sec-WebSocket-Protocol: chat

//

final class HandshakePhase {

    private final ServerSocketChannel ssc;

    HandshakePhase(InetSocketAddress address) {

        requireNonNull(address);

        try {

            ssc = ServerSocketChannel.open();

            ssc.bind(address);

        } catch (IOException e) {

            throw new UncheckedIOException(e);

        }

    }

    //

    // Returned CF completes normally after the handshake has been performed

    //

    CompletableFuture<SocketChannel> afterHandshake(

            Function<List<String>, List<String>> mapping) {

        return CompletableFuture.supplyAsync(

                () -> {

                    SocketChannel socketChannel = accept();

                    try {

                        StringBuilder request = new StringBuilder();

                        if (!readRequest(socketChannel, request)) {

                            throw new IllegalStateException();

                        }

                        List<String> strings = Arrays.asList(

                                request.toString().split("\r\n")

                        );

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

                        writeResponse(socketChannel, response);

                        return socketChannel;

                    } catch (Throwable t) {

                        try {

                            socketChannel.close();

                        } catch (IOException ignored) { }

                        throw t;

                    }

                });

    }

    CompletableFuture<SocketChannel> afterHandshake() {

        return afterHandshake((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(StandardCharsets.ISO_8859_1));

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

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

            return response;

        });

    }

    private 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;

    }

    URI getURI() {

        InetSocketAddress a;

        try {

            a = (InetSocketAddress) ssc.getLocalAddress();

        } catch (IOException e) {

            throw new UncheckedIOException(e);

        }

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

    }

    private int read(SocketChannel socketChannel, ByteBuffer buffer) {

        try {

            int num = socketChannel.read(buffer);

            if (num == -1) {

                throw new IllegalStateException("Unexpected EOF");

            }

            assert socketChannel.isBlocking() && num > 0;

            return num;

        } catch (IOException e) {

            throw new UncheckedIOException(e);

        }

    }

    private SocketChannel accept() {

        SocketChannel socketChannel = null;

        try {

            socketChannel = ssc.accept();

            socketChannel.configureBlocking(true);

        } catch (IOException e) {

            if (socketChannel != null) {

                try {

                    socketChannel.close();

                } catch (IOException ignored) { }

            }

            throw new UncheckedIOException(e);

        }

        return socketChannel;

    }

    private boolean readRequest(SocketChannel socketChannel,

                                StringBuilder request) {

        ByteBuffer buffer = ByteBuffer.allocateDirect(512);

        read(socketChannel, buffer);

        CharBuffer decoded;

        buffer.flip();

        try {

            decoded =

                    StandardCharsets.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 socketChannel,

                               List<String> response) {

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

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

        ByteBuffer encoded;

        try {

            encoded =

                    StandardCharsets.ISO_8859_1.newEncoder().encode(CharBuffer.wrap(s));

        } catch (CharacterCodingException e) {

            throw new UncheckedIOException(e);

        }

        write(socketChannel, encoded);

    }

    private void write(SocketChannel socketChannel, ByteBuffer buffer) {

        try {

            while (buffer.hasRemaining()) {

                socketChannel.write(buffer);

            }

        } catch (IOException e) {

            try {

                socketChannel.close();

            } catch (IOException ignored) { }

            throw new UncheckedIOException(e);

        }

    }

}