/*
 * 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 org.reactivestreams.Subscription;

import reactor.core.CoreSubscriber;
import reactor.util.annotation.Nullable;

Subscriber that makes sure signals are delivered sequentially in case the onNext, onError or onComplete methods are
called concurrently.

 The implementation uses synchronized (this) to ensure mutual exclusion. 


Note that the class implements Subscription to save on allocation.
Type parameters:
<T> – the value type/**
 * Subscriber that makes sure signals are delivered sequentially in case the onNext, onError or onComplete methods are
 * called concurrently.
 * <p>
 * <p>
 * The implementation uses {@code synchronized (this)} to ensure mutual exclusion.
 * <p>
 * <p>
 * Note that the class implements Subscription to save on allocation.
 *
 * @param <T> the value type
 */
final class SerializedSubscriber<T> implements InnerOperator<T, T> {

	final CoreSubscriber<? super T> actual;

	boolean drainLoopInProgress;

	boolean concurrentlyAddedContent;

	volatile boolean done;

	volatile boolean cancelled;

	LinkedArrayNode<T> head;

	LinkedArrayNode<T> tail;

	Throwable error;

	Subscription s;

	SerializedSubscriber(CoreSubscriber<? super T> actual) {
		this.actual = actual;
	}

	@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 (cancelled) {
			Operators.onDiscard(t, actual.currentContext());
			return;
		}
		if (done) {
			Operators.onNextDropped(t, actual.currentContext());
			return;
		}

		synchronized (this) {
			if (cancelled) {
				Operators.onDiscard(t, actual.currentContext());
				return;
			}
			if (done) {
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}

			if (drainLoopInProgress) {
				serAdd(t);
				concurrentlyAddedContent = true;
				return;
			}

			drainLoopInProgress = true;
		}

		actual.onNext(t);

		serDrainLoop(actual);
	}

	@Override
	public void onError(Throwable t) {
		if (cancelled || done) {
			return;
		}

		synchronized (this) {
			if (cancelled || done) {
				return;
			}

			done = true;
			error = t;

			if (drainLoopInProgress) {
				concurrentlyAddedContent = true;
				return;
			}
		}

		actual.onError(t);
	}

	@Override
	public void onComplete() {
		if (cancelled || done) {
			return;
		}

		synchronized (this) {
			if (cancelled || done) {
				return;
			}

			done = true;

			if (drainLoopInProgress) {
				concurrentlyAddedContent = true;
				return;
			}
		}

		actual.onComplete();
	}

	@Override
	public void request(long n) {
		s.request(n);
	}

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

	void serAdd(T value) {
		if (cancelled) {
			Operators.onDiscard(value, actual.currentContext());
			return;
		}

		LinkedArrayNode<T> t = tail;

		if (t == null) {
			t = new LinkedArrayNode<>(value);

			head = t;
			tail = t;
		}
		else {
			if (t.count == LinkedArrayNode.DEFAULT_CAPACITY) {
				LinkedArrayNode<T> n = new LinkedArrayNode<>(value);

				t.next = n;
				tail = n ;
			}
			else {
				t.array[t.count++] = value;
			}
		}
		if (cancelled) {
			//this case could mean serDrainLoop "won" and cleared an old view of the nodes first,
			// then we added "from scratch", so we remain with a single-element node containing `value`
			// => we can simply discard `value`
			Operators.onDiscard(value, actual.currentContext());
		}
	}

	void serDrainLoop(CoreSubscriber<? super T> actual) {
		for (; ; ) {

			if (cancelled) {
				synchronized (this) {
					discardMultiple(this.head);
				}
				return;
			}

			boolean d;
			Throwable e;
			LinkedArrayNode<T> n;

			synchronized (this) {
				if (cancelled) {
					discardMultiple(this.head);
					return;
				}

				if (!concurrentlyAddedContent) {
					drainLoopInProgress = false;
					return;
				}

				concurrentlyAddedContent = false;

				d = done;
				e = error;
				n = head;

				head = null;
				tail = null;
			}

			while (n != null) {

				T[] arr = n.array;
				int c = n.count;

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

					if (cancelled) {
						synchronized (this) {
							discardMultiple(n);
						}
						return;
					}

					actual.onNext(arr[i]);
				}

				n = n.next;
			}

			if (cancelled) {
				synchronized (this) {
					discardMultiple(this.head);
				}
				return;
			}

			if (e != null) {
				actual.onError(e);
				return;
			}
			else if (d) {
				actual.onComplete();
				return;
			}
		}
	}

	private void discardMultiple(LinkedArrayNode<T> head) {
		LinkedArrayNode<T> originalHead = head;
		LinkedArrayNode<T> h = head;
		while (h != null) {
			//discard
			for (int i = 0; i < h.count; i++) {
				Operators.onDiscard(h.array[i], actual.currentContext());
			}
			h = h.next;

			if (h == null && this.head != originalHead) {
				originalHead = this.head;
				h = originalHead;
			}
		}
	}

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

	@Override
	@Nullable
	public Object scanUnsafe(Attr key) {
		if (key == Attr.PARENT) return s;
		if (key == Attr.ERROR) return error;
		if (key == Attr.BUFFERED) return producerCapacity();
		if (key == Attr.CAPACITY) return LinkedArrayNode.DEFAULT_CAPACITY;
		if (key == Attr.CANCELLED) return cancelled;
		if (key == Attr.TERMINATED) return done;

		return InnerOperator.super.scanUnsafe(key);
	}

	int producerCapacity() {
		LinkedArrayNode<T> node = tail;
		if(node != null){
			return node.count;
		}
		return 0;
	}

	
Node in a linked array list that is only appended.
Type parameters:
<T> – the value type/**
	 * Node in a linked array list that is only appended.
	 *
	 * @param <T> the value type
	 */
	static final class LinkedArrayNode<T> {

		static final int DEFAULT_CAPACITY = 16;

		final T[] array;
		int count;

		LinkedArrayNode<T> next;

		@SuppressWarnings("unchecked")
		LinkedArrayNode(T value) {
			array = (T[]) new Object[DEFAULT_CAPACITY];
			array[0] = value;
			count = 1;
		}
	}
}