/*

 * Copyright (c) 2019, 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.InputStream;

import java.nio.ByteBuffer;

import java.nio.charset.StandardCharsets;

import java.security.SecureRandom;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Iterator;

import java.util.List;

import java.util.Objects;

import java.util.Random;

import java.util.concurrent.Flow.Publisher;

import java.util.concurrent.Flow.Subscriber;

import java.util.concurrent.Flow.Subscription;

import java.util.stream.Stream;

/*

 * S for Support.

 *

 * Auxiliary methods for tests that check conformance with reactive streams

 * specification.

 *

 * Short name is for the sake of convenience calling this class' static methods.

 * It could've been called Support or TckSupport, but then we would need to

 * place this class in its own package so as to use "import static".

 */

public class S {

    private static final Random RANDOM = new SecureRandom();

    private S() { }

    public static List<ByteBuffer> listOfBuffersFromBufferOfNBytes(int nBytes) {

        return scatterBuffer(bufferOfNRandomBytes(nBytes));

    }

    /*

     * Spreads the remaining contents of the given byte buffer across a number

     * of buffers put into a list.

     */

    public static List<ByteBuffer> scatterBuffer(ByteBuffer src) {

        List<ByteBuffer> buffers = new ArrayList<>();

        while (src.hasRemaining()) {

            // We do not allow empty buffers ~~~~~~~~~~~~~~~~v

            int capacity = RANDOM.nextInt(src.remaining()) + 1;

            ByteBuffer b = ByteBuffer.allocate(capacity);

            for (int i = 0; i < capacity; i++) {

                b.put(src.get());

            }

            b.flip();

            buffers.add(b);

        }

        return List.copyOf(buffers);

    }

    public static ByteBuffer bufferOfNRandomBytes(int capacity) {

        return ByteBuffer.wrap(arrayOfNRandomBytes(capacity));

    }

    public static byte[] arrayOfNRandomBytes(int nBytes) {

        byte[] contents = new byte[nBytes];

        RANDOM.nextBytes(contents);

        return contents;

    }

    public static InputStream inputStreamOfNReads(long n) {

        return new NReadsInputStream(n);

    }

    /*

     * Convenience method for testing publishers.

     */

    public static byte[] arrayOfNRandomBytes(long nBytes) {

        return arrayOfNRandomBytes((int) nBytes);

    }

    public static ByteBuffer bufferOfNRandomASCIIBytes(int capacity) {

        String alphaNumeric = "abcdefghijklmnopqrstuvwxyz1234567890";

        StringBuilder builder = new StringBuilder(capacity);

        for (int i = 0; i < capacity; i++) {

            int idx = RANDOM.nextInt(alphaNumeric.length());

            builder.append(alphaNumeric.charAt(idx));

        }

        return ByteBuffer.wrap(builder.toString().getBytes(

                StandardCharsets.US_ASCII));

    }

    /*

     * Returns a simple non-compliant Subscriber.

     *

     * This Subscriber is useful for testing our adaptors and wrappers, to make

     * sure they do not delegate RS compliance to the underlying (and foreign to

     * java.net.http codebase) Subscribers, but rather comply themselves.

     *

     * Here's an example:

     *

     *     public void onSubscribe(Subscription s) {

     *         delegate.onSubscribe(s);

     *     }

     *

     * The snippet above cannot be considered a good implementation of a

     * Subscriber if `delegate` is an unknown Subscriber. In this case the

     * implementation should independently check all the rules from the RS spec

     * related to subscribers.

     */

    public static <T> Subscriber<T> nonCompliantSubscriber() {

        return new Subscriber<>() {

            @Override

            public void onSubscribe(Subscription subscription) {

                subscription.request(Long.MAX_VALUE);

            }

            @Override

            public void onNext(T item) { }

            @Override

            public void onError(Throwable throwable) { }

            @Override

            public void onComplete() { }

        };

    }

    public static int randomIntUpTo(int bound) {

        return RANDOM.nextInt(bound);

    }

    /*

     * Signals an error to its subscribers immediately after subscription.

     */

    public static <T> Publisher<T> newErroredPublisher() {

        return subscriber -> {

            subscriber.onSubscribe(new Subscription() {

                @Override

                public void request(long n) { }

                @Override

                public void cancel() { }

            });

            subscriber.onError(new IOException());

        };

    }

    /*

     * Publishes the elements obtained from the stream and signals completion.

     * Can be cancelled, but cannot signal an error.

     *

     * This trivial ad-hoc implementation of Publisher was created so as to

     * publish lists of byte buffers. We can publish ByteBuffer, but we can't

     * seem to publish List<ByteBuffer> since there's no readily available

     * publisher of those, nor there's a simple adaptor.

     */

    public static <T> Publisher<T> publisherOfStream(Stream<? extends T> stream)

    {

        if (stream == null) {

            throw new NullPointerException();

        }

        return new Publisher<T>() {

            @Override

            public void subscribe(Subscriber<? super T> subscriber) {

                if (subscriber == null) {

                    throw new NullPointerException();

                }

                Subscription subscription = new Subscription() {

                    boolean inOnNext; // recursion control

                    volatile boolean cancelled;

                    long demand;

                    final Iterator<? extends T> supply = stream.iterator();

                    @Override

                    public void request(long n) {

                        demand = demand + n < 0 ? Long.MAX_VALUE : demand + n;

                        if (inOnNext) {

                            return;

                        }

                        if (cancelled)

                            return;

                        if (n <= 0) {

                            cancelled = true;

                            subscriber.onError(new IllegalArgumentException(

                                    "non-positive subscription request"));

                            return;

                        }

                        while (supply.hasNext() && demand > 0 && !cancelled) {

                            demand--;

                            inOnNext = true;

                            try {

                                T item = supply.next();

                                subscriber.onNext(item);

                            } finally {

                                inOnNext = false;

                            }

                        }

                        if (!supply.hasNext()) {

                            cancelled = true;

                            subscriber.onComplete();

                        }

                    }

                    @Override

                    public void cancel() {

                        cancelled = true;

                    }

                };

                subscriber.onSubscribe(subscription);

            }

        };

    }

    static final class NReadsInputStream extends InputStream {

        private static final int EOF = -1;

        private long readsLeft;

        NReadsInputStream(long n) {

            if (n < 0) {

                throw new IllegalArgumentException(String.valueOf(n));

            }

            this.readsLeft = n;

        }

        @Override

        public int read() {

            if (readsLeft == 0L) {

                return EOF;

            }

            readsLeft--;

            return S.randomIntUpTo(256);

        }

        @Override

        public int read(byte[] b, int off, int len) {

            Objects.checkFromIndexSize(off, len, b.length);

            // Must return 0 if len == 0,

            // even if there are no more reads left

            if (len == 0) {

                return 0;

            }

            if (readsLeft == 0L) {

                return EOF;

            }

            readsLeft--;

            // At least one byte MUST be read, but we can read

            // less than `len` bytes

            int r = RANDOM.nextInt(len) + 1;

            for (int i = 0; i < r; i++) {

                b[i] = (byte) randomIntUpTo(256);

            }

            return r;

        }

    }

}