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.observers;

import io.reactivex.Observer;
import io.reactivex.annotations.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;

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

    static final int QUEUE_LINK_SIZE = 4;

    Disposable upstream;

    boolean emitting;
    AppendOnlyLinkedArrayList<Object> queue;

    volatile boolean done;

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

    
Construct a SerializedObserver 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 Observer, not null (not verified)
delayError – if true, errors are emitted after regular values have been emitted/**
     * Construct a SerializedObserver 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 Observer, not null (not verified)
     * @param delayError if true, errors are emitted after regular values have been emitted
     */
    public SerializedObserver(@NonNull Observer<? super T> actual, boolean delayError) {
        this.downstream = actual;
        this.delayError = delayError;
    }

    @Override
    public void onSubscribe(@NonNull Disposable d) {
        if (DisposableHelper.validate(this.upstream, d)) {
            this.upstream = d;

            downstream.onSubscribe(this);
        }
    }

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

    @Override
    public boolean isDisposed() {
        return upstream.isDisposed();
    }

    @Override
    public void onNext(@NonNull T t) {
        if (done) {
            return;
        }
        if (t == null) {
            upstream.dispose();
            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(@NonNull 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;
            }
        }
    }
}