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Reactor API for the HiveMQ MQTT Client
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/*
 * Copyright 2018-present HiveMQ and the HiveMQ Community
 *
 * 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.
 */

package com.hivemq.client.rx.reactor;

import com.hivemq.client.internal.rx.reactor.CoreWithSingleStrictSubscriber;
import com.hivemq.client.internal.rx.reactor.operators.FluxWithSingleFrom;
import com.hivemq.client.internal.rx.reactor.operators.FluxWithSingleMap;
import com.hivemq.client.internal.rx.reactor.operators.FluxWithSinglePublishOn;
import com.hivemq.client.internal.util.Checks;
import com.hivemq.client.rx.reactivestreams.PublisherWithSingle;
import com.hivemq.client.rx.reactivestreams.WithSingleSubscriber;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.core.CoreSubscriber;
import reactor.core.publisher.Flux;
import reactor.core.scheduler.Scheduler;
import reactor.util.concurrent.Queues;
import reactor.util.context.Context;

import java.util.NoSuchElementException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Consumer;
import java.util.function.Function;

/**
 * A {@link Flux} which emits a flow of items of type F and a single item of type S.
 *
 * @param  the type of the flow of items.
 * @param  the type of the single item.
 * @author Silvio Giebl
 * @since 1.2
 */
public abstract class FluxWithSingle extends Flux implements CorePublisherWithSingle {

    /**
     * Decorate the specified {@link PublisherWithSingle} with the {@link FluxWithSingle} API.
     *
     * @param source the source to decorate.
     * @param     the type of the flow items.
     * @param     the type of the single item.
     * @return a new {@link FluxWithSingle}.
     */
    public static  @NotNull FluxWithSingle from(
            final @NotNull PublisherWithSingle source) {

        if (source instanceof FluxWithSingle) {
            //noinspection unchecked
            return (FluxWithSingle) source;
        }
        return new FluxWithSingleFrom<>(source);
    }

    /**
     * Run onSingle, onNext, onComplete and onError on a supplied {@link Scheduler.Worker}.
     *
     * @param scheduler a {@link Scheduler} providing the {@link Scheduler.Worker} where to publish.
     * @return a {@link FluxWithSingle} producing asynchronously.
     * @see Flux#publishOn(Scheduler)
     */
    public final @NotNull FluxWithSingle publishBothOn(final @NotNull Scheduler scheduler) {
        return publishBothOn(scheduler, Queues.SMALL_BUFFER_SIZE);
    }

    /**
     * Run onSingle, onNext, onComplete and onError on a supplied {@link Scheduler.Worker}.
     *
     * @param scheduler see {@link Flux#publishOn(Scheduler, int)}
     * @param prefetch  see {@link Flux#publishOn(Scheduler, int)}
     * @return a {@link FluxWithSingle} producing asynchronously.
     * @see Flux#publishOn(Scheduler, int)
     */
    public final @NotNull FluxWithSingle publishBothOn(final @NotNull Scheduler scheduler, final int prefetch) {
        return publishBothOn(scheduler, true, prefetch);
    }

    /**
     * Run onSingle, onNext, onComplete and onError on a supplied {@link Scheduler.Worker}.
     *
     * @param scheduler  see {@link Flux#publishOn(Scheduler, boolean, int)}
     * @param delayError see {@link Flux#publishOn(Scheduler, boolean, int)}
     * @param prefetch   see {@link Flux#publishOn(Scheduler, boolean, int)}
     * @return a {@link FluxWithSingle} producing asynchronously.
     * @see Flux#publishOn(Scheduler, boolean, int)
     */
    public final @NotNull FluxWithSingle publishBothOn(
            final @NotNull Scheduler scheduler, final boolean delayError, final int prefetch) {

        Checks.notNull(scheduler, "Scheduler");
        return new FluxWithSinglePublishOn<>(this, scheduler, delayError, prefetch);
    }

    /**
     * Transform the single item emitted by this {@link FluxWithSingle} by applying a synchronous function to it.
     *
     * @param singleMapper the synchronous transforming {@link Function} for the single item.
     * @param          the transformed type of the single item.
     * @return a transformed {@link FluxWithSingle}.
     */
    public final  @NotNull FluxWithSingle mapSingle(
            final @NotNull Function singleMapper) {

        Checks.notNull(singleMapper, "Single mapper");
        return FluxWithSingleMap.mapSingle(this, singleMapper);
    }

    /**
     * Transform the items emitted by this {@link FluxWithSingle} by applying a synchronous function to each item.
     *
     * @param fluxMapper   the synchronous transforming {@link Function} for the flow of items.
     * @param singleMapper the synchronous transforming {@link Function} for the single item.
     * @param          the transformed type of the flow items.
     * @param          the transformed type of the single item.
     * @return a transformed {@link FluxWithSingle}.
     */
    public final  @NotNull FluxWithSingle mapBoth(
            final @NotNull Function fluxMapper,
            final @NotNull Function singleMapper) {

        Checks.notNull(fluxMapper, "Flux mapper");
        Checks.notNull(singleMapper, "Single mapper");
        return FluxWithSingleMap.mapBoth(this, fluxMapper, singleMapper);
    }

    /**
     * Add behavior (side-effect) triggered when this {@link FluxWithSingle} emits the single item.
     *
     * @param singleConsumer the callback to call on {@link WithSingleSubscriber#onSingle}.
     * @return an observed {@link FluxWithSingle}.
     */
    public final @NotNull FluxWithSingle doOnSingle(final @NotNull Consumer singleConsumer) {
        Checks.notNull(singleConsumer, "Single consumer");
        return FluxWithSingleMap.mapSingle(this, s -> {
            singleConsumer.accept(s);
            return s;
        });
    }

    @Override
    public final void subscribeBoth(final @NotNull WithSingleSubscriber subscriber) {
        if (subscriber instanceof CoreWithSingleSubscriber) {
            //noinspection unchecked
            subscribeBoth((CoreWithSingleSubscriber) subscriber);
        } else {
            Checks.notNull(subscriber, "Subscriber");
            subscribeBoth(new CoreWithSingleStrictSubscriber<>(subscriber));
        }
    }

    /**
     * {@link #subscribe() Subscribes} to this Flowable and returns a future for the single item.
     * 
     *   The future will complete with the single item if this {@link FluxWithSingle} emits a single item.
     *   
The future will complete exceptionally with a {@link NoSuchElementException} if this {@link
     *     FluxWithSingle} completes but no single item was emitted.
     *   
The future will complete exceptionally with the exception emitted by this {@link FluxWithSingle} if it
     *     errors before the single item was emitted.
     *   
Cancelling the future will cancel this {@link FluxWithSingle} also when the future already completed
     *     normally or exceptionally.
     * 
     *
     * @return a future for the single item.
     * @see #subscribe()
     */
    public final @NotNull CompletableFuture subscribeSingleFuture() {
        final SingleFutureSubscriber singleFutureSubscriber = new SingleFutureSubscriber<>(this);
        final CompletableFuture future = singleFutureSubscriber.getFutureBeforeSubscribe();
        singleFutureSubscriber.subscribe();
        return future;
    }

    /**
     * {@link #subscribe(Consumer) Subscribes} to this Flowable and returns a future for the single item.
     * 
     *   The future will complete with the single item if this {@link FluxWithSingle} emits a single item.
     *   
The future will complete exceptionally with a {@link NoSuchElementException} if this {@link
     *     FluxWithSingle} completes but no single item was emitted.
     *   
The future will complete exceptionally with the exception emitted by this {@link FluxWithSingle} if it
     *     errors before the single item was emitted.
     *   
Cancelling the future will cancel this {@link FluxWithSingle} also when the future already completed
     *     normally or exceptionally.
     * 
     *
     * @param consumer see {@link #subscribe(Consumer)}
     * @return a future for the single item.
     * @see #subscribe(Consumer)
     */
    public final @NotNull CompletableFuture subscribeSingleFuture(final @NotNull Consumer consumer) {
        final SingleFutureSubscriber singleFutureSubscriber = new SingleFutureSubscriber<>(this);
        final CompletableFuture future = singleFutureSubscriber.getFutureBeforeSubscribe();
        singleFutureSubscriber.subscribe(consumer);
        return future;
    }

    /**
     * {@link #subscribe(Consumer, Consumer) Subscribes} to this Flowable and returns a future for the single item.
     * 
     *   The future will complete with the single item if this {@link FluxWithSingle} emits a single item.
     *   
The future will complete exceptionally with a {@link NoSuchElementException} if this {@link
     *     FluxWithSingle} completes but no single item was emitted.
     *   
The future will complete exceptionally with the exception emitted by this {@link FluxWithSingle} if it
     *     errors before the single item was emitted.
     *   
Cancelling the future will cancel this {@link FluxWithSingle} also when the future already completed
     *     normally or exceptionally.
     * 
     *
     * @param consumer      see {@link #subscribe(Consumer, Consumer)}
     * @param errorConsumer see {@link #subscribe(Consumer, Consumer)}
     * @return a future for the single item.
     * @see #subscribe(Consumer, Consumer)
     */
    public final @NotNull CompletableFuture subscribeSingleFuture(
            final @NotNull Consumer consumer, final @NotNull Consumer errorConsumer) {

        final SingleFutureSubscriber singleFutureSubscriber = new SingleFutureSubscriber<>(this);
        final CompletableFuture future = singleFutureSubscriber.getFutureBeforeSubscribe();
        singleFutureSubscriber.subscribe(consumer, errorConsumer);
        return future;
    }

    /**
     * {@link #subscribe(Consumer, Consumer, Runnable) Subscribes} to this Flowable and returns a future for the single
     * item.
     * 
     *   The future will complete with the single item if this {@link FluxWithSingle} emits a single item.
     *   
The future will complete exceptionally with a {@link NoSuchElementException} if this {@link
     *     FluxWithSingle} completes but no single item was emitted.
     *   
The future will complete exceptionally with the exception emitted by this {@link FluxWithSingle} if it
     *     errors before the single item was emitted.
     *   
Cancelling the future will cancel this {@link FluxWithSingle} also when the future already completed
     *     normally or exceptionally.
     * 
     *
     * @param consumer         see {@link #subscribe(Consumer, Consumer, Runnable)}
     * @param errorConsumer    see {@link #subscribe(Consumer, Consumer, Runnable)}
     * @param completeConsumer see {@link #subscribe(Consumer, Consumer, Runnable)}
     * @return a future for the single item.
     * @see #subscribe(Consumer, Consumer, Runnable)
     */
    public final @NotNull CompletableFuture subscribeSingleFuture(
            final @NotNull Consumer consumer,
            final @NotNull Consumer errorConsumer,
            final @NotNull Runnable completeConsumer) {

        final SingleFutureSubscriber singleFutureSubscriber = new SingleFutureSubscriber<>(this);
        final CompletableFuture future = singleFutureSubscriber.getFutureBeforeSubscribe();
        singleFutureSubscriber.subscribe(consumer, errorConsumer, completeConsumer);
        return future;
    }

    /**
     * {@link #subscribe(Consumer, Consumer, Runnable, Context) Subscribes} to this Flowable and returns a future for
     * the single item.
     * 
     *   The future will complete with the single item if this {@link FluxWithSingle} emits a single item.
     *   
The future will complete exceptionally with a {@link NoSuchElementException} if this {@link
     *     FluxWithSingle} completes but no single item was emitted.
     *   
The future will complete exceptionally with the exception emitted by this {@link FluxWithSingle} if it
     *     errors before the single item was emitted.
     *   
Cancelling the future will cancel this {@link FluxWithSingle} also when the future already completed
     *     normally or exceptionally.
     * 
     *
     * @param consumer         see {@link #subscribe(Consumer, Consumer, Runnable, Context)}
     * @param errorConsumer    see {@link #subscribe(Consumer, Consumer, Runnable, Context)}
     * @param completeConsumer see {@link #subscribe(Consumer, Consumer, Runnable, Context)}
     * @param initialContext   see {@link #subscribe(Consumer, Consumer, Runnable, Context)}
     * @return a future for the single item.
     * @see #subscribe(Consumer, Consumer, Runnable, Context)
     */
    public final @NotNull CompletableFuture subscribeSingleFuture(
            final @NotNull Consumer consumer,
            final @NotNull Consumer errorConsumer,
            final @NotNull Runnable completeConsumer,
            final @NotNull Context initialContext) {

        final SingleFutureSubscriber singleFutureSubscriber = new SingleFutureSubscriber<>(this);
        final CompletableFuture future = singleFutureSubscriber.getFutureBeforeSubscribe();
        singleFutureSubscriber.subscribe(consumer, errorConsumer, completeConsumer, initialContext);
        return future;
    }

    /**
     * {@link #subscribe(Subscriber) Subscribes} to this Flowable and returns a future for the single item.
     * 
     *   The future will complete with the single item if this {@link FluxWithSingle} emits a single item.
     *   
The future will complete exceptionally with a {@link NoSuchElementException} if this {@link
     *     FluxWithSingle} completes but no single item was emitted.
     *   
The future will complete exceptionally with the exception emitted by this {@link FluxWithSingle} if it
     *     errors before the single item was emitted.
     *   
Cancelling the future will cancel this {@link FluxWithSingle} also when the future already completed
     *     normally or exceptionally.
     * 
     *
     * @param subscriber see {@link #subscribe(Subscriber)}
     * @return a future for the single item.
     * @see #subscribe(Subscriber)
     */
    public final @NotNull CompletableFuture subscribeSingleFuture(final @NotNull Subscriber subscriber) {
        final SingleFutureSubscriber singleFutureSubscriber = new SingleFutureSubscriber<>(this);
        final CompletableFuture future = singleFutureSubscriber.getFutureBeforeSubscribe();
        singleFutureSubscriber.subscribe(subscriber);
        return future;
    }

    private static class SingleFutureSubscriber extends Flux
            implements CoreWithSingleSubscriber, Subscription {

        private final @NotNull FluxWithSingle source;
        private @Nullable Subscriber subscriber;
        private final @NotNull AtomicReference<@Nullable Subscription> subscription = new AtomicReference<>();
        private final @NotNull AtomicReference<@Nullable CompletableFuture> future =
                new AtomicReference<>(new CompletableFuture() {
                    @Override
                    public boolean cancel(final boolean mayInterruptIfRunning) {
                        future.set(null);
                        SingleFutureSubscriber.this.cancel();
                        return super.cancel(mayInterruptIfRunning);
                    }
                });

        SingleFutureSubscriber(final @NotNull FluxWithSingle source) {
            this.source = source;
        }

        @NotNull CompletableFuture getFutureBeforeSubscribe() {
            final CompletableFuture future = this.future.get();
            assert future != null;
            return future;
        }

        @Override
        public void subscribe(final @NotNull CoreSubscriber subscriber) {
            this.subscriber = subscriber;
            source.subscribeBoth(this);
        }

        @Override
        public void onSubscribe(final @NotNull Subscription subscription) {
            assert subscriber != null;
            if (!this.subscription.compareAndSet(null, subscription)) {
                cancel(subscription);
            }
            subscriber.onSubscribe(this);
        }

        @Override
        public void onSingle(final @NotNull S s) {
            final CompletableFuture future = this.future.getAndSet(null);
            if (future != null) {
                future.complete(s);
            }
        }

        @Override
        public void onNext(final @NotNull F f) {
            assert subscriber != null;
            subscriber.onNext(f);
        }

        @Override
        public void onComplete() {
            assert subscriber != null;
            final CompletableFuture future = this.future.getAndSet(null);
            if (future != null) {
                future.completeExceptionally(new NoSuchElementException());
            }
            subscriber.onComplete();
        }

        @Override
        public void onError(final @NotNull Throwable t) {
            assert subscriber != null;
            final CompletableFuture future = this.future.getAndSet(null);
            if (future != null) {
                future.completeExceptionally(t);
            }
            subscriber.onError(t);
        }

        @Override
        public void request(final long n) {
            final Subscription subscription = this.subscription.get();
            assert subscription != null;
            if (subscription != this) {
                subscription.request(n);
            }
        }

        @Override
        public void cancel() {
            final Subscription subscription = this.subscription.getAndSet(this);
            if ((subscription != null) && (subscription != this)) {
                cancel(subscription);
            }
        }

        private void cancel(final @NotNull Subscription subscription) {
            subscription.cancel();
            final CompletableFuture future = this.future.getAndSet(null);
            if (future != null) {
                future.cancel(false);
            }
        }
    }
}