/*

 * Copyright (c) 2015, 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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

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package java.net.http;

import java.io.UncheckedIOException;

import java.io.IOException;

import java.net.URI;

import java.net.URISyntaxException;

import java.nio.charset.StandardCharsets;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.security.SecureRandom;

import java.util.Arrays;

import java.util.Base64;

import java.util.Collection;

import java.util.List;

import java.util.concurrent.CompletableFuture;

import java.util.function.Predicate;

import java.util.stream.Collectors;

import static java.lang.String.format;

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

import static java.net.http.WSUtils.logger;

import static java.net.http.WSUtils.webSocketSpecViolation;

final class WSOpeningHandshake {

    private static final String HEADER_CONNECTION = "Connection";

    private static final String HEADER_UPGRADE = "Upgrade";

    private static final String HEADER_ACCEPT = "Sec-WebSocket-Accept";

    private static final String HEADER_EXTENSIONS = "Sec-WebSocket-Extensions";

    private static final String HEADER_KEY = "Sec-WebSocket-Key";

    private static final String HEADER_PROTOCOL = "Sec-WebSocket-Protocol";

    private static final String HEADER_VERSION = "Sec-WebSocket-Version";

    private static final String VALUE_VERSION = "13"; // WebSocket's lucky number

    private static final SecureRandom srandom = new SecureRandom();

    private final MessageDigest sha1;

    {

        try {

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

        } catch (NoSuchAlgorithmException e) {

            // Shouldn't happen:

            // SHA-1 must be available in every Java platform implementation

            throw new InternalError("Minimum platform requirements are not met", e);

        }

    }

    private final HttpRequest request;

    private final Collection<String> subprotocols;

    private final String nonce;

    WSOpeningHandshake(WSBuilder b) {

        URI httpURI = createHttpUri(b.getUri());

        HttpRequest.Builder requestBuilder = b.getClient().request(httpURI);

        }

        Collection<String> s = b.getSubprotocols();

        if (!s.isEmpty()) {

            String p = s.stream().collect(Collectors.joining(", "));

            requestBuilder.header(HEADER_PROTOCOL, p);

        }

        requestBuilder.header(HEADER_VERSION, VALUE_VERSION);

        this.nonce = createNonce();

        requestBuilder.header(HEADER_KEY, this.nonce);

        this.request = requestBuilder.GET();

        HttpRequestImpl r = (HttpRequestImpl) this.request;

        r.isWebSocket(true);

        r.setSystemHeader(HEADER_UPGRADE, "websocket");

        r.setSystemHeader(HEADER_CONNECTION, "Upgrade");

        this.subprotocols = s;

    }

    private URI createHttpUri(URI webSocketUri) {

        // FIXME: check permission for WebSocket URI and translate it into http/https permission

        logger.log(TRACE, "->createHttpUri(''{0}'')", webSocketUri);

        String httpScheme = webSocketUri.getScheme().equalsIgnoreCase("ws")

                ? "http"

                : "https";

        try {

            URI uri = new URI(httpScheme,

                    webSocketUri.getUserInfo(),

                    webSocketUri.getHost(),

                    webSocketUri.getPort(),

                    webSocketUri.getPath(),

                    webSocketUri.getQuery(),

                    null);

            logger.log(TRACE, "<-createHttpUri: ''{0}''", uri);

            return uri;

        } catch (URISyntaxException e) {

            // Shouldn't happen: URI invariant

            throw new InternalError("Error translating WebSocket URI to HTTP URI", e);

        }

    }

    CompletableFuture<Result> performAsync() {

        // The whole dancing with thenCompose instead of thenApply is because

        // WebSocketHandshakeException is a checked exception

        return request.responseAsync()

                .thenCompose(response -> {

                    try {

                        Result result = handleResponse(response);

                        return CompletableFuture.completedFuture(result);

                    } catch (WebSocketHandshakeException e) {

                        return CompletableFuture.failedFuture(e);

                    } catch (UncheckedIOException ee) {

                        return CompletableFuture.failedFuture(ee.getCause());

                    }

                });

    }

    private Result handleResponse(HttpResponse response) throws WebSocketHandshakeException {

        // By this point all redirects, authentications, etc. (if any) must have

        // been done by the httpClient used by the WebSocket; so only 101 is

        // expected

        int statusCode = response.statusCode();

        if (statusCode != 101) {

            String m = webSocketSpecViolation("1.3.",

                    "Unable to complete handshake; HTTP response status code "

                            + statusCode

            );

            throw new WebSocketHandshakeException(m, response);

        }

        HttpHeaders h = response.headers();

        checkHeader(h, response, HEADER_UPGRADE, v -> v.equalsIgnoreCase("websocket"));

        checkHeader(h, response, HEADER_CONNECTION, v -> v.equalsIgnoreCase("Upgrade"));

        checkVersion(response, h);

        checkAccept(response, h);

        checkExtensions(response, h);

        String subprotocol = checkAndReturnSubprotocol(response, h);

        RawChannel channel = null;

        try {

            channel = ((HttpResponseImpl) response).rawChannel();

        } catch (IOException e) {

            throw new UncheckedIOException(e);

        }

        return new Result(subprotocol, channel);

    }

    private void checkExtensions(HttpResponse response, HttpHeaders headers)

            throws WebSocketHandshakeException {

        List<String> ext = headers.allValues(HEADER_EXTENSIONS);

        if (!ext.isEmpty()) {

            String m = webSocketSpecViolation("4.1.",

                    "Server responded with extension(s) though none were requested "

                            + Arrays.toString(ext.toArray())

            );

            throw new WebSocketHandshakeException(m, response);

        }

    }

    private String checkAndReturnSubprotocol(HttpResponse response, HttpHeaders headers)

            throws WebSocketHandshakeException {

        assert response.statusCode() == 101 : response.statusCode();

        List<String> sp = headers.allValues(HEADER_PROTOCOL);

        int size = sp.size();

        if (size == 0) {

            // In this case the subprotocol requested (if any) by the client

            // doesn't matter. If there is no such header in the response, then

            // the server doesn't want to use any subprotocol

            return null;

        } else if (size > 1) {

            // We don't know anything about toString implementation of this

            // list, so let's create an array

            String m = webSocketSpecViolation("4.1.",

                    "Server responded with multiple subprotocols: "

                            + Arrays.toString(sp.toArray())

            );

            throw new WebSocketHandshakeException(m, response);

        } else {

            String selectedSubprotocol = sp.get(0);

            if (this.subprotocols.contains(selectedSubprotocol)) {

                return selectedSubprotocol;

            } else {

                String m = webSocketSpecViolation("4.1.",

                        format("Server responded with a subprotocol " +

                                        "not among those requested: '%s'",

                                selectedSubprotocol));

                throw new WebSocketHandshakeException(m, response);

            }

        }

    }

    private void checkAccept(HttpResponse response, HttpHeaders headers)

            throws WebSocketHandshakeException {

        assert response.statusCode() == 101 : response.statusCode();

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

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

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

        checkHeader(headers, response, HEADER_ACCEPT, actual -> actual.trim().equals(expected));

    }

    private void checkVersion(HttpResponse response, HttpHeaders headers)

            throws WebSocketHandshakeException {

        assert response.statusCode() == 101 : response.statusCode();

        List<String> versions = headers.allValues(HEADER_VERSION);

        if (versions.isEmpty()) { // That's normal and expected

            return;

        }

        String m = webSocketSpecViolation("4.4.",

                "Server responded with version(s) "

                        + Arrays.toString(versions.toArray()));

        throw new WebSocketHandshakeException(m, response);

    }

    //

    // Checks whether there's only one value for the header with the given name

    // and the value satisfies the predicate.

    //

    private static void checkHeader(HttpHeaders headers,

                                    HttpResponse response,

                                    String headerName,

                                    Predicate<? super String> valuePredicate)

            throws WebSocketHandshakeException {

        assert response.statusCode() == 101 : response.statusCode();

        List<String> values = headers.allValues(headerName);

        if (values.isEmpty()) {

            String m = webSocketSpecViolation("4.1.",

                    format("Server response field '%s' is missing", headerName)

            );

            throw new WebSocketHandshakeException(m, response);

        } else if (values.size() > 1) {

            String m = webSocketSpecViolation("4.1.",

                    format("Server response field '%s' has multiple values", headerName)

            );

            throw new WebSocketHandshakeException(m, response);

        }

        if (!valuePredicate.test(values.get(0))) {

            String m = webSocketSpecViolation("4.1.",

                    format("Server response field '%s' is incorrect", headerName)

            );

            throw new WebSocketHandshakeException(m, response);

        }

    }

    private static String createNonce() {

        byte[] bytes = new byte[16];

        srandom.nextBytes(bytes);

        return Base64.getEncoder().encodeToString(bytes);

    }

    static final class Result {

        final String subprotocol;

        final RawChannel channel;

        private Result(String subprotocol, RawChannel channel) {

            this.subprotocol = subprotocol;

            this.channel = channel;

        }

    }

}