Copyright (c) 2016-present, RxJava Contributors.
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.
/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * 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 io.reactivex.subscribers;

import org.reactivestreams.*;

import io.reactivex.FlowableSubscriber;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;

Serializes access to the onNext, onError and onComplete methods of another Subscriber.
Note that onSubscribe(Subscription) is not serialized in respect of the other methods so make sure the onSubscribe is called with a non-null Subscription before any of the other methods are called. 
The implementation assumes that the actual Subscriber's methods don't throw.
Type parameters:
<T> – the value type/**
 * Serializes access to the onNext, onError and onComplete methods of another Subscriber.
 *
 * <p>Note that {@link #onSubscribe(Subscription)} is not serialized in respect of the other methods so
 * make sure the {@code onSubscribe} is called with a non-null {@code Subscription}
 * before any of the other methods are called.
 *
 * <p>The implementation assumes that the actual Subscriber's methods don't throw.
 *
 * @param <T> the value type
 */
public final class SerializedSubscriber<T> implements FlowableSubscriber<T>, Subscription {
    final Subscriber<? super T> downstream;
    final boolean delayError;

    static final int QUEUE_LINK_SIZE = 4;

    Subscription upstream;

    boolean emitting;
    AppendOnlyLinkedArrayList<Object> queue;

    volatile boolean done;

    
Construct a SerializedSubscriber by wrapping the given actual Subscriber.
Params:
downstream – the actual Subscriber, not null (not verified)/**
     * Construct a SerializedSubscriber by wrapping the given actual Subscriber.
     * @param downstream the actual Subscriber, not null (not verified)
     */
    public SerializedSubscriber(Subscriber<? super T> downstream) {
        this(downstream, false);
    }

    
Construct a SerializedSubscriber by wrapping the given actual Observer and
optionally delaying the errors till all regular values have been emitted
from the internal buffer.
Params:
actual – the actual Subscriber, not null (not verified)
delayError – if true, errors are emitted after regular values have been emitted/**
     * Construct a SerializedSubscriber by wrapping the given actual Observer and
     * optionally delaying the errors till all regular values have been emitted
     * from the internal buffer.
     * @param actual the actual Subscriber, not null (not verified)
     * @param delayError if true, errors are emitted after regular values have been emitted
     */
    public SerializedSubscriber(Subscriber<? super T> actual, boolean delayError) {
        this.downstream = actual;
        this.delayError = delayError;
    }

    @Override
    public void onSubscribe(Subscription s) {
        if (SubscriptionHelper.validate(this.upstream, s)) {
            this.upstream = s;
            downstream.onSubscribe(this);
        }
    }

    @Override
    public void onNext(T t) {
        if (done) {
            return;
        }
        if (t == null) {
            upstream.cancel();
            onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
            return;
        }
        synchronized (this) {
            if (done) {
                return;
            }
            if (emitting) {
                AppendOnlyLinkedArrayList<Object> q = queue;
                if (q == null) {
                    q = new AppendOnlyLinkedArrayList<Object>(QUEUE_LINK_SIZE);
                    queue = q;
                }
                q.add(NotificationLite.next(t));
                return;
            }
            emitting = true;
        }

        downstream.onNext(t);

        emitLoop();
    }

    @Override
    public void onError(Throwable t) {
        if (done) {
            RxJavaPlugins.onError(t);
            return;
        }
        boolean reportError;
        synchronized (this) {
            if (done) {
                reportError = true;
            } else
            if (emitting) {
                done = true;
                AppendOnlyLinkedArrayList<Object> q = queue;
                if (q == null) {
                    q = new AppendOnlyLinkedArrayList<Object>(QUEUE_LINK_SIZE);
                    queue = q;
                }
                Object err = NotificationLite.error(t);
                if (delayError) {
                    q.add(err);
                } else {
                    q.setFirst(err);
                }
                return;
            } else {
                done = true;
                emitting = true;
                reportError = false;
            }
        }

        if (reportError) {
            RxJavaPlugins.onError(t);
            return;
        }

        downstream.onError(t);
        // no need to loop because this onError is the last event
    }

    @Override
    public void onComplete() {
        if (done) {
            return;
        }
        synchronized (this) {
            if (done) {
                return;
            }
            if (emitting) {
                AppendOnlyLinkedArrayList<Object> q = queue;
                if (q == null) {
                    q = new AppendOnlyLinkedArrayList<Object>(QUEUE_LINK_SIZE);
                    queue = q;
                }
                q.add(NotificationLite.complete());
                return;
            }
            done = true;
            emitting = true;
        }

        downstream.onComplete();
        // no need to loop because this onComplete is the last event
    }

    void emitLoop() {
        for (;;) {
            AppendOnlyLinkedArrayList<Object> q;
            synchronized (this) {
                q = queue;
                if (q == null) {
                    emitting = false;
                    return;
                }
                queue = null;
            }

            if (q.accept(downstream)) {
                return;
            }
        }
    }

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

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