/*
 * Java Genetic Algorithm Library (jenetics-7.2.0).
 * Copyright (c) 2007-2023 Franz Wilhelmstötter
 *
 * Licensed 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.
 *
 * Author:
 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics.util;

import static java.util.Objects.requireNonNull;

import java.util.concurrent.CancellationException;
import java.util.concurrent.Executor;
import java.util.concurrent.Flow;
import java.util.concurrent.Flow.Subscriber;
import java.util.concurrent.SubmissionPublisher;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.BiConsumer;
import java.util.stream.Stream;

import io.jenetics.internal.util.Lifecycle.ExtendedCloseable;

/**
 * This class allows creating a reactive {@link Flow.Publisher} from a given
 * Java {@link Stream}.
 *
 * <pre>{@code
 * final Stream<Long> stream = engine.stream()
 *     .limit(33)
 *     .map(EvolutionResult::generation);
 *
 * try (var publisher = new StreamPublisher<Long>()) {
 *     publisher.subscribe(new Subscriber<>() {
 *         private Subscription subscription;
 *         \@Override
 *         public void onSubscribe(final Subscription subscription) {
 *             (this.subscription = subscription).request(1);
 *         }
 *         \@Override
 *         public void onNext(final Long g) {
 *             System.out.println("Got new generation: " + g);
 *             subscription.request(1);
 *         }
 *         \@Override
 *         public void onError(final Throwable throwable) {
 *         }
 *         \@Override
 *         public void onComplete() {
 *             System.out.println("Evolution completed.");
 *         }
 *     });
 *
 *     // Attaching the stream, starts the element publishing.
 *     publisher.attach(stream);
 *
 *     ...
 * }
 * }</pre>
 *
 * @param <T> the element type of the publisher
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 6.0
 * @since 6.0
 */
public class StreamPublisher<T> extends SubmissionPublisher<T> {

        private final Object _lock = new Object(){};

        private final AtomicBoolean _proceed = new AtomicBoolean(true);

        private Stream<? extends T> _stream;
        private Thread _thread;

        /**
         * Creates a new {@code StreamPublisher} using the given {@code Executor}
         * for async delivery to subscribers, with the given maximum buffer size for
         * each subscriber.
         *
         * @param executor the executor to use for async delivery, supporting
         *        creation of at least one independent thread
         * @param maxBufferCapacity the maximum capacity for each subscriber's buffer
         * @param handler if non-null, procedure to invoke upon exception thrown in
         *        method {@code onNext}
         * @throws NullPointerException if one of the arguments is {@code null}
         * @throws IllegalArgumentException if maxBufferCapacity not positive
         */
        public StreamPublisher(
                final Executor executor,
                final int maxBufferCapacity,
                final BiConsumer<? super Subscriber<? super T>, ? super Throwable> handler
        ) {
                super(executor, maxBufferCapacity, handler);
        }

        /**
         * Creates a new {@code StreamPublisher} using the given {@code Executor}
         * for async delivery to subscribers, with the given maximum buffer size for
         * each subscriber, and no handler for Subscriber exceptions in method
         * {@link java.util.concurrent.Flow.Subscriber#onNext(Object)}.
         *
         * @param executor the executor to use for async delivery, supporting
         *        creation of at least one independent thread
         * @param maxBufferCapacity the maximum capacity for each subscriber's buffer
         * @throws NullPointerException if the given {@code executor} is {@code null}
         * @throws IllegalArgumentException if maxBufferCapacity not positive
         */
        public StreamPublisher(final Executor executor, final int maxBufferCapacity) {
                super(executor, maxBufferCapacity);
        }

        /**
         * Creates a new publisher using the {@code ForkJoinPool.commonPool()} for
         * async delivery to subscribers (unless it does not support a parallelism
         * level of at least two, in which case, a new Thread is created to run each
         * task), with maximum buffer capacity of {@code Flow.defaultBufferSize()},
         * and no handler for Subscriber exceptions in method onNext.
         */
        public StreamPublisher() {
        }

        /**
         * Attaches the given stream to the publisher. This method automatically
         * starts the publishing of the elements read from the stream. The attached
         * {@code stream} is closed, when {@code this} publisher is closed.
         *
         * @param stream the {@code stream} to attach
         * @throws NullPointerException if the given {@code stream} is {@code null}
         * @throws IllegalStateException if a stream is already attached to this
         *         publisher
         */
        public synchronized void attach(final Stream<? extends T> stream) {
                requireNonNull(stream);

                synchronized (_lock) {
                        if (_stream != null) {
                                throw new IllegalStateException(
                                        "Already attached evolution stream."
                                );
                        }

                        _stream = stream.takeWhile(e -> _proceed.get());
                        _thread = new Thread(() -> {
                                try {
                                        _stream.forEach(this::submit);
                                        close();
                                } catch(CancellationException e) {
                                        Thread.currentThread().interrupt();
                                        close();
                                } catch (Throwable e) {
                                        closeExceptionally(e);
                                }
                        });
                        _thread.start();
                }
        }

        /**
         * Unless already closed, issues {@code onComplete} signals to current
         * subscribers, and disallows subsequent attempts to publish. Upon return,
         * this method does NOT guarantee that all subscribers have already completed.
         */
        @Override
        public void close() {
                synchronized (_lock) {
                        final var closeable = ExtendedCloseable.of(
                                () -> { if (_thread != null) _thread.interrupt(); },
                                () -> { if (_stream != null) _stream.close(); }
                        );

                        _proceed.set(false);
                        closeable.silentClose();
                }
                super.close();
        }

}