/*
 * Copyright (c) 2011-2017 Pivotal Software Inc, 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.concurrent.atomic.AtomicIntegerFieldUpdater;

import org.reactivestreams.Subscription;
import reactor.core.CoreSubscriber;
import reactor.core.Fuseable;
import reactor.core.Fuseable.ConditionalSubscriber;
import reactor.core.Fuseable.QueueSubscription;
import reactor.util.annotation.Nullable;

Takes only the first N values from the source Publisher.

If N is zero, the subscriber gets completed if the source completes, signals an error or
signals its first value (which is not not relayed though).
Type parameters:
<T> – the value type
See Also:
Reactive-Streams-Commons/**
 * Takes only the first N values from the source Publisher.
 * <p>
 * If N is zero, the subscriber gets completed if the source completes, signals an error or
 * signals its first value (which is not not relayed though).
 *
 * @param <T> the value type
 * @see <a href="https://github.com/reactor/reactive-streams-commons">Reactive-Streams-Commons</a>
 */
final class FluxTake<T> extends InternalFluxOperator<T, T> {

	final long n;

	FluxTake(Flux<? extends T> source, long n) {
		super(source);
		if (n < 0) {
			throw new IllegalArgumentException("n >= 0 required but it was " + n);
		}
		this.n = n;
	}

	@Override
	@SuppressWarnings("unchecked")
	public CoreSubscriber<? super T> subscribeOrReturn(CoreSubscriber<? super T> actual) {
		if (actual instanceof ConditionalSubscriber) {
			return new TakeConditionalSubscriber<>((ConditionalSubscriber<? super T>) actual, n);
		}
		else {
			return new TakeSubscriber<>(actual, n);
		}
	}

	@Override
	public int getPrefetch() {
		return Integer.MAX_VALUE;
	}

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

	static final class TakeSubscriber<T>
			implements InnerOperator<T, T> {

		final CoreSubscriber<? super T> actual;

		final long n;

		long remaining;

		Subscription s;

		boolean done;

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

		public TakeSubscriber(CoreSubscriber<? super T> actual, long n) {
			this.actual = actual;
			this.n = n;
			this.remaining = n;
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				if (n == 0) {
					s.cancel();
					done = true;
					Operators.complete(actual);
				}
				else {
					this.s = s;
					actual.onSubscribe(this);
				}
			}
		}

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

			long r = remaining;

			if (r == 0) {
				s.cancel();
				onComplete();
				return;
			}

			remaining = --r;
			boolean stop = r == 0L;

			actual.onNext(t);

			if (stop) {
				s.cancel();

				onComplete();
			}
		}

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

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

		@Override
		public void request(long n) {
			if (wip == 0 && WIP.compareAndSet(this, 0, 1)) {
				if (n >= this.n) {
					s.request(Long.MAX_VALUE);
				} else {
					s.request(n);
				}
				return;
			}

			s.request(n);
		}

		@Override
		public void cancel() {
			s.cancel();
		}

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

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public CoreSubscriber<? super T> actual() {
			return actual;
		}
	}

	static final class TakeConditionalSubscriber<T>
			implements ConditionalSubscriber<T>, InnerOperator<T, T> {

		final ConditionalSubscriber<? super T> actual;

		final long n;

		long remaining;

		Subscription s;

		boolean done;

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

		TakeConditionalSubscriber(ConditionalSubscriber<? super T> actual,
				long n) {
			this.actual = actual;
			this.n = n;
			this.remaining = n;
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.s, s)) {
				if (n == 0) {
					s.cancel();
					done = true;
					Operators.complete(actual);
				}
				else {
					this.s = s;
					actual.onSubscribe(this);
				}
			}
		}

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

			long r = remaining;

			if (r == 0) {
				s.cancel();
				onComplete();
				return;
			}

			remaining = --r;
			boolean stop = r == 0L;

			actual.onNext(t);

			if (stop) {
				s.cancel();

				onComplete();
			}
		}

		@Override
		public boolean tryOnNext(T t) {
			if (done) {
				Operators.onNextDropped(t, actual.currentContext());
				return true;
			}

			long r = remaining;

			if (r == 0) {
				s.cancel();
				onComplete();
				return true;
			}

			remaining = --r;
			boolean stop = r == 0L;

			boolean b = actual.tryOnNext(t);

			if (stop) {
				s.cancel();

				onComplete();
			}
			return b;
		}

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

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

		@Override
		public void request(long n) {
			if (wip == 0 && WIP.compareAndSet(this, 0, 1)) {
				if (n >= this.n) {
					s.request(Long.MAX_VALUE);
				}
				else {
					s.request(n);
				}
				return;
			}

			s.request(n);
		}

		@Override
		public void cancel() {
			s.cancel();
		}

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

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public CoreSubscriber<? super T> actual() {
			return actual;
		}
	}

	static final class TakeFuseableSubscriber<T>
			implements QueueSubscription<T>, InnerOperator<T, T> {

		final CoreSubscriber<? super T> actual;

		final long n;

		long remaining;

		QueueSubscription<T> qs;

		boolean done;

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

		int inputMode;

		TakeFuseableSubscriber(CoreSubscriber<? super T> actual, long n) {
			this.actual = actual;
			this.n = n;
			this.remaining = n;
		}

		@SuppressWarnings("unchecked")
		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(this.qs, s)) {
				if (n == 0) {
					s.cancel();
					done = true;
					Operators.complete(actual);
				}
				else {
					this.qs = (QueueSubscription<T>) s;
					actual.onSubscribe(this);
				}
			}
		}

		@Override
		public void onNext(T t) {

			if (inputMode == Fuseable.ASYNC) {
				actual.onNext(null);
				return;
			}
			if (done) {
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}

			long r = remaining;

			if (r == 0) {
				qs.cancel();
				onComplete();
				return;
			}

			remaining = --r;
			boolean stop = r == 0L;

			actual.onNext(t);

			if (stop) {
				qs.cancel();

				onComplete();
			}
		}

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

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

		@Override
		public void request(long n) {
			if (wip == 0 && WIP.compareAndSet(this, 0, 1)) {
				if (n >= this.n) {
					qs.request(Long.MAX_VALUE);
				}
				else {
					qs.request(n);
				}
				return;
			}

			qs.request(n);
		}

		@Override
		public void cancel() {
			qs.cancel();
		}

		@Override
		@Nullable
		public Object scanUnsafe(Attr key) {
			if (key == Attr.TERMINATED) return done;
			if (key == Attr.PARENT) return qs;
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;

			return InnerOperator.super.scanUnsafe(key);
		}

		@Override
		public CoreSubscriber<? super T> actual() {
			return actual;
		}

		@Override
		public int requestFusion(int requestedMode) {
			int m = qs.requestFusion(requestedMode);
			this.inputMode = m;
			return m;
		}

		@Override
		@Nullable
		public T poll() {
			if (done) {
				return null;
			}
			long r = remaining;
			T v = qs.poll();
			if (r == 0L) {
				done = true;
				if (inputMode == Fuseable.ASYNC) {
					qs.cancel();
					actual.onComplete();
				}
				return null;
			}


			if (v != null) {
				remaining = --r;
				if (r == 0L) {
					if (!done) {
						done = true;
						if (inputMode == Fuseable.ASYNC) {
							qs.cancel();
							actual.onComplete();
						}
					}
				}
			}

			return v;
		}

		@Override
		public boolean isEmpty() {
			return remaining == 0 || qs.isEmpty();
		}

		@Override
		public void clear() {
			qs.clear();
		}

		@Override
		public int size() {
			return qs.size();
		}
	}

}