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/*
 * Copyright (c) 2016-2022 VMware Inc. or its affiliates, All Rights Reserved.
 *
 * 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
 *
 *   https://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 reactor.core.publisher;

import java.util.ArrayDeque;
import java.util.Objects;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.function.Supplier;
import java.util.stream.Stream;

import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;

import reactor.core.CoreSubscriber;
import reactor.core.Disposable;
import reactor.core.Scannable;
import reactor.util.annotation.Nullable;
import reactor.util.context.Context;

import static reactor.core.Exceptions.wrapSource;

/**
 * Splits the source sequence into possibly overlapping publishers.
 *
 * @param  the value type
 *
 * @see https://github.com/reactor/reactive-streams-commons
 */
final class FluxWindow extends InternalFluxOperator> {

	final int size;

	final int skip;

	final Supplier> processorQueueSupplier;

	final Supplier>> overflowQueueSupplier;

	FluxWindow(Flux source,
			int size,
			Supplier> processorQueueSupplier) {
		super(source);
		if (size <= 0) {
			throw new IllegalArgumentException("size > 0 required but it was " + size);
		}
		this.size = size;
		this.skip = size;
		this.processorQueueSupplier =
				Objects.requireNonNull(processorQueueSupplier, "processorQueueSupplier");
		this.overflowQueueSupplier = null; // won't be needed here
	}

	FluxWindow(Flux source,
			int size,
			int skip,
			Supplier> processorQueueSupplier,
			Supplier>> overflowQueueSupplier) {
		super(source);
		if (size <= 0) {
			throw new IllegalArgumentException("size > 0 required but it was " + size);
		}
		if (skip <= 0) {
			throw new IllegalArgumentException("skip > 0 required but it was " + skip);
		}
		this.size = size;
		this.skip = skip;
		this.processorQueueSupplier =
				Objects.requireNonNull(processorQueueSupplier, "processorQueueSupplier");
		this.overflowQueueSupplier =
				Objects.requireNonNull(overflowQueueSupplier, "overflowQueueSupplier");
	}

	@Override
	public CoreSubscriber subscribeOrReturn(CoreSubscriber> actual) {
		if (skip == size) {
			return new WindowExactSubscriber<>(actual,
					size,
					processorQueueSupplier);
		}
		else if (skip > size) {
			return new WindowSkipSubscriber<>(actual,
					size, skip, processorQueueSupplier);
		}
		else {
			return new WindowOverlapSubscriber<>(actual,
					size,
					skip, processorQueueSupplier, overflowQueueSupplier.get());
		}
	}

	@Override
	public Object scanUnsafe(Attr key) {
		if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
		return super.scanUnsafe(key);
	}

	static final class WindowExactSubscriber
			implements Disposable, InnerOperator> {

		final CoreSubscriber> actual;

		final Supplier> processorQueueSupplier;

		final int size;

		volatile int cancelled;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater CANCELLED =
				AtomicIntegerFieldUpdater.newUpdater(WindowExactSubscriber.class, "cancelled");

		volatile int windowCount;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater WINDOW_COUNT =
				AtomicIntegerFieldUpdater.newUpdater(WindowExactSubscriber.class, "windowCount");

		int index;

		Subscription s;

		Sinks.Many window;

		boolean done;

		WindowExactSubscriber(CoreSubscriber> actual,
				int size,
				Supplier> processorQueueSupplier) {
			this.actual = actual;
			this.size = size;
			this.processorQueueSupplier = processorQueueSupplier;
			WINDOW_COUNT.lazySet(this, 1);
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				this.s = s;
				actual.onSubscribe(this);
			}
		}

		@Override
		public void onNext(T t) {
			if (done) {
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}

			int i = index;

			Sinks.Many w = window;
			if (cancelled == 0 && i == 0) {
				WINDOW_COUNT.getAndIncrement(this);

				w = Sinks.unsafe().many().unicast().onBackpressureBuffer(processorQueueSupplier.get(), this);
				window = w;

				actual.onNext(w.asFlux());
			}

			i++;

			w.emitNext(t, Sinks.EmitFailureHandler.FAIL_FAST);

			if (i == size) {
				index = 0;
				window = null;
				w.emitComplete(Sinks.EmitFailureHandler.FAIL_FAST);
			}
			else {
				index = i;
			}
		}

		@Override
		public void onError(Throwable t) {
			if (done) {
				Operators.onErrorDropped(t, actual.currentContext());
				return;
			}
			done = true;
			Sinks.Many w = window;
			if (w != null) {
				window = null;
				w.emitError(wrapSource(t), Sinks.EmitFailureHandler.FAIL_FAST);
			}

			actual.onError(t);
		}

		@Override
		public void onComplete() {
			if (done) {
				return;
			}
			done = true;
			Sinks.Many w = window;
			if (w != null) {
				window = null;
				w.emitComplete(Sinks.EmitFailureHandler.FAIL_FAST);
			}

			actual.onComplete();
		}

		@Override
		public void request(long n) {
			if (Operators.validate(n)) {
				long u = Operators.multiplyCap(size, n);
				s.request(u);
			}
		}

		@Override
		public void cancel() {
			if (CANCELLED.compareAndSet(this, 0, 1)) {
				dispose();
			}
		}

		@Override
		public void dispose() {
			if (WINDOW_COUNT.decrementAndGet(this) == 0) {
				s.cancel();
			}
		}

		@Override
		public CoreSubscriber> actual() {
			return actual;
		}

		@Override
		public boolean isDisposed() {
			return cancelled == 1 || done;
		}

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.PARENT) return s;
			if (key == Attr.CANCELLED) return cancelled == 1;
			if (key == Attr.CAPACITY) return size;
			if (key == Attr.TERMINATED) return done;
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public Stream inners() {
			return Stream.of(Scannable.from(window));
		}
	}

	static final class WindowSkipSubscriber
			implements Disposable, InnerOperator> {

		final CoreSubscriber> actual;
		final Context                         ctx;

		final Supplier> processorQueueSupplier;

		final int size;

		final int skip;

		volatile int cancelled;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater CANCELLED =
				AtomicIntegerFieldUpdater.newUpdater(WindowSkipSubscriber.class, "cancelled");

		volatile int windowCount;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater WINDOW_COUNT =
				AtomicIntegerFieldUpdater.newUpdater(WindowSkipSubscriber.class, "windowCount");

		volatile int firstRequest;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater FIRST_REQUEST =
				AtomicIntegerFieldUpdater.newUpdater(WindowSkipSubscriber.class,
						"firstRequest");

		int index;

		Subscription s;

		Sinks.Many window;

		boolean done;

		WindowSkipSubscriber(CoreSubscriber> actual,
				int size,
				int skip,
				Supplier> processorQueueSupplier) {
			this.actual = actual;
			this.ctx = actual.currentContext();
			this.size = size;
			this.skip = skip;
			this.processorQueueSupplier = processorQueueSupplier;
			WINDOW_COUNT.lazySet(this, 1);
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				this.s = s;
				actual.onSubscribe(this);
			}
		}

		@Override
		public void onNext(T t) {
			if (done) {
				Operators.onNextDropped(t, ctx);
				return;
			}

			int i = index;

			Sinks.Many w = window;
			if (i == 0) {
				WINDOW_COUNT.getAndIncrement(this);

				w = Sinks.unsafe().many().unicast().onBackpressureBuffer(processorQueueSupplier.get(), this);
				window = w;

				actual.onNext(w.asFlux());
			}

			i++;

			if (w != null) {
				w.emitNext(t, Sinks.EmitFailureHandler.FAIL_FAST);
			}
			else {
				Operators.onDiscard(t, ctx);
			}

			if (i == size) {
				window = null;
				if (w != null) {
					w.emitComplete(Sinks.EmitFailureHandler.FAIL_FAST);
				}
			}

			if (i == skip) {
				index = 0;
			}
			else {
				index = i;
			}
		}

		@Override
		public void onError(Throwable t) {
			if (done) {
				Operators.onErrorDropped(t, ctx);
				return;
			}
			done = true;

			Sinks.Many w = window;
			if (w != null) {
				window = null;
				w.emitError(wrapSource(t), Sinks.EmitFailureHandler.FAIL_FAST);
			}

			actual.onError(t);
		}

		@Override
		public void onComplete() {
			if (done) {
				return;
			}
			done = true;

			Sinks.Many w = window;
			if (w != null) {
				window = null;
				w.emitComplete(Sinks.EmitFailureHandler.FAIL_FAST);
			}

			actual.onComplete();
		}

		@Override
		public void request(long n) {
			if (Operators.validate(n)) {
				if (firstRequest == 0 && FIRST_REQUEST.compareAndSet(this, 0, 1)) {
					long u = Operators.multiplyCap(size, n);
					long v = Operators.multiplyCap(skip - size, n - 1);
					long w = Operators.addCap(u, v);
					s.request(w);
				}
				else {
					long u = Operators.multiplyCap(skip, n);
					s.request(u);
				}
			}
		}

		@Override
		public void cancel() {
			if (CANCELLED.compareAndSet(this, 0, 1)) {
				dispose();
			}
		}

		@Override
		public boolean isDisposed() {
			return cancelled == 1 || done;
		}

		@Override
		public void dispose() {
			if (WINDOW_COUNT.decrementAndGet(this) == 0) {
				s.cancel();
			}
		}

		@Override
		public CoreSubscriber> actual() {
			return actual;
		}

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.PARENT) return s;
			if (key == Attr.CANCELLED) return cancelled == 1;
			if (key == Attr.CAPACITY) return size;
			if (key == Attr.TERMINATED) return done;
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public Stream inners() {
			return Stream.of(Scannable.from(window));
		}
	}

	static final class WindowOverlapSubscriber extends ArrayDeque>
			implements Disposable, InnerOperator> {

		final CoreSubscriber> actual;

		final Supplier> processorQueueSupplier;

		final Queue> queue;

		final int size;

		final int skip;

		volatile int cancelled;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater CANCELLED =
				AtomicIntegerFieldUpdater.newUpdater(WindowOverlapSubscriber.class,
						"cancelled");

		volatile int windowCount;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater WINDOW_COUNT =
				AtomicIntegerFieldUpdater.newUpdater(WindowOverlapSubscriber.class,
						"windowCount");

		volatile int firstRequest;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater FIRST_REQUEST =
				AtomicIntegerFieldUpdater.newUpdater(WindowOverlapSubscriber.class,
						"firstRequest");

		volatile long requested;
		@SuppressWarnings("rawtypes")
		static final AtomicLongFieldUpdater REQUESTED =
				AtomicLongFieldUpdater.newUpdater(WindowOverlapSubscriber.class,
						"requested");

		volatile int wip;
		@SuppressWarnings("rawtypes")
		static final AtomicIntegerFieldUpdater WIP =
				AtomicIntegerFieldUpdater.newUpdater(WindowOverlapSubscriber.class, "wip");

		int index;

		int produced;

		Subscription s;

		volatile boolean done;
		Throwable error;

		WindowOverlapSubscriber(CoreSubscriber> actual,
				int size,
				int skip,
				Supplier> processorQueueSupplier,
				Queue> overflowQueue) {
			this.actual = actual;
			this.size = size;
			this.skip = skip;
			this.processorQueueSupplier = processorQueueSupplier;
			WINDOW_COUNT.lazySet(this, 1);
			this.queue = overflowQueue;
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				this.s = s;
				actual.onSubscribe(this);
			}
		}

		@Override
		public void onNext(T t) {
			if (done) {
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}

			int i = index;

			if (i == 0) {
				if (cancelled == 0) {
					WINDOW_COUNT.getAndIncrement(this);

					Sinks.Many w = Sinks.unsafe().many().unicast().onBackpressureBuffer(processorQueueSupplier.get(), this);

					offer(w);

					queue.offer(w);
					drain();
				}
			}

			i++;

			for (Sinks.Many w : this) {
				w.emitNext(t, Sinks.EmitFailureHandler.FAIL_FAST);
			}

			int p = produced + 1;
			if (p == size) {
				produced = p - skip;

				Sinks.Many w = poll();
				if (w != null) {
					w.emitComplete(Sinks.EmitFailureHandler.FAIL_FAST);
				}
			}
			else {
				produced = p;
			}

			if (i == skip) {
				index = 0;
			}
			else {
				index = i;
			}
		}

		@Override
		public void onError(Throwable t) {
			if (done) {
				Operators.onErrorDropped(t, actual.currentContext());
				return;
			}
			done = true;

			for (Sinks.Many w : this) {
				w.emitError(wrapSource(t), Sinks.EmitFailureHandler.FAIL_FAST);
			}
			clear();

			error = t;
			drain();
		}

		@Override
		public void onComplete() {
			if (done) {
				return;
			}
			done = true;

			for (Sinks.Many w : this) {
				w.emitComplete(Sinks.EmitFailureHandler.FAIL_FAST);
			}
			clear();

			drain();
		}

		void drain() {
			if (WIP.getAndIncrement(this) != 0) {
				return;
			}

			final Subscriber> a = actual;
			final Queue> q = queue;
			int missed = 1;

			for (; ; ) {

				long r = requested;
				long e = 0;

				while (e != r) {
					boolean d = done;

					Sinks.Many t = q.poll();

					boolean empty = t == null;

					if (checkTerminated(d, empty, a, q)) {
						return;
					}

					if (empty) {
						break;
					}

					a.onNext(t.asFlux());

					e++;
				}

				if (e == r) {
					if (checkTerminated(done, q.isEmpty(), a, q)) {
						return;
					}
				}

				if (e != 0L && r != Long.MAX_VALUE) {
					REQUESTED.addAndGet(this, -e);
				}

				missed = WIP.addAndGet(this, -missed);
				if (missed == 0) {
					break;
				}
			}
		}

		boolean checkTerminated(boolean d, boolean empty, Subscriber a, Queue q) {
			if (cancelled == 1) {
				q.clear();
				return true;
			}

			if (d) {
				Throwable e = error;

				if (e != null) {
					q.clear();
					a.onError(e);
					return true;
				}
				else if (empty) {
					a.onComplete();
					return true;
				}
			}

			return false;
		}

		@Override
		public void request(long n) {
			if (Operators.validate(n)) {

				Operators.addCap(REQUESTED, this, n);

				if (firstRequest == 0 && FIRST_REQUEST.compareAndSet(this, 0, 1)) {
					long u = Operators.multiplyCap(skip, n - 1);
					long v = Operators.addCap(size, u);
					s.request(v);
				}
				else {
					long u = Operators.multiplyCap(skip, n);
					s.request(u);
				}

				drain();
			}
		}

		@Override
		public void cancel() {
			if (CANCELLED.compareAndSet(this, 0, 1)) {
				dispose();
			}
		}

		@Override
		public void dispose() {
			if (WINDOW_COUNT.decrementAndGet(this) == 0) {
				s.cancel();
			}
		}

		@Override
		public CoreSubscriber> actual() {
			return actual;
		}

		@Override
		public boolean isDisposed() {
			return cancelled == 1 || done;
		}

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.PARENT) return s;
			if (key == Attr.CANCELLED) return cancelled == 1;
			if (key == Attr.CAPACITY) return size;
			if (key == Attr.TERMINATED) return done;
			if (key == Attr.LARGE_BUFFERED) return (long) queue.size() + size();
			if (key == Attr.BUFFERED) {
				long realBuffered = (long) queue.size() + size();
				if (realBuffered < Integer.MAX_VALUE) return (int) realBuffered;
				return Integer.MIN_VALUE;
			}
			if (key == Attr.ERROR) return error;
			if (key == Attr.REQUESTED_FROM_DOWNSTREAM) return requested;
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public Stream inners() {
			return Stream.of(toArray())
			             .map(Scannable::from);
		}
	}

}