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.internal.operators.observable;

import java.util.concurrent.atomic.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.fuseable.SimplePlainQueue;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.util.AtomicThrowable;
import io.reactivex.plugins.RxJavaPlugins;

Merges an Observable and a Single by emitting the items of the Observable and the success
value of the Single and waiting until both the Observable and Single terminate normally.
History: 2.1.10 - experimental
Type parameters:
<T> – the element type of the Observable
Since:
2.2/**
 * Merges an Observable and a Single by emitting the items of the Observable and the success
 * value of the Single and waiting until both the Observable and Single terminate normally.
 * <p>History: 2.1.10 - experimental
 * @param <T> the element type of the Observable
 * @since 2.2
 */
public final class ObservableMergeWithSingle<T> extends AbstractObservableWithUpstream<T, T> {

    final SingleSource<? extends T> other;

    public ObservableMergeWithSingle(Observable<T> source, SingleSource<? extends T> other) {
        super(source);
        this.other = other;
    }

    @Override
    protected void subscribeActual(Observer<? super T> observer) {
        MergeWithObserver<T> parent = new MergeWithObserver<T>(observer);
        observer.onSubscribe(parent);
        source.subscribe(parent);
        other.subscribe(parent.otherObserver);
    }

    static final class MergeWithObserver<T> extends AtomicInteger
    implements Observer<T>, Disposable {

        private static final long serialVersionUID = -4592979584110982903L;

        final Observer<? super T> downstream;

        final AtomicReference<Disposable> mainDisposable;

        final OtherObserver<T> otherObserver;

        final AtomicThrowable error;

        volatile SimplePlainQueue<T> queue;

        T singleItem;

        volatile boolean disposed;

        volatile boolean mainDone;

        volatile int otherState;

        static final int OTHER_STATE_HAS_VALUE = 1;

        static final int OTHER_STATE_CONSUMED_OR_EMPTY = 2;

        MergeWithObserver(Observer<? super T> downstream) {
            this.downstream = downstream;
            this.mainDisposable = new AtomicReference<Disposable>();
            this.otherObserver = new OtherObserver<T>(this);
            this.error = new AtomicThrowable();
        }

        @Override
        public void onSubscribe(Disposable d) {
            DisposableHelper.setOnce(mainDisposable, d);
        }

        @Override
        public void onNext(T t) {
            if (compareAndSet(0, 1)) {
                downstream.onNext(t);
                if (decrementAndGet() == 0) {
                    return;
                }
            } else {
                SimplePlainQueue<T> q = getOrCreateQueue();
                q.offer(t);
                if (getAndIncrement() != 0) {
                    return;
                }
            }
            drainLoop();
        }

        @Override
        public void onError(Throwable ex) {
            if (error.addThrowable(ex)) {
                DisposableHelper.dispose(otherObserver);
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }

        @Override
        public void onComplete() {
            mainDone = true;
            drain();
        }

        @Override
        public boolean isDisposed() {
            return DisposableHelper.isDisposed(mainDisposable.get());
        }

        @Override
        public void dispose() {
            disposed = true;
            DisposableHelper.dispose(mainDisposable);
            DisposableHelper.dispose(otherObserver);
            if (getAndIncrement() == 0) {
                queue = null;
                singleItem = null;
            }
        }

        void otherSuccess(T value) {
            if (compareAndSet(0, 1)) {
                downstream.onNext(value);
                otherState = OTHER_STATE_CONSUMED_OR_EMPTY;
            } else {
                singleItem = value;
                otherState = OTHER_STATE_HAS_VALUE;
                if (getAndIncrement() != 0) {
                    return;
                }
            }
            drainLoop();
        }

        void otherError(Throwable ex) {
            if (error.addThrowable(ex)) {
                DisposableHelper.dispose(mainDisposable);
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }

        SimplePlainQueue<T> getOrCreateQueue() {
            SimplePlainQueue<T> q = queue;
            if (q == null) {
                q = new SpscLinkedArrayQueue<T>(bufferSize());
                queue = q;
            }
            return q;
        }

        void drain() {
            if (getAndIncrement() == 0) {
                drainLoop();
            }
        }

        void drainLoop() {
            Observer<? super T> actual = this.downstream;
            int missed = 1;
            for (;;) {

                for (;;) {
                    if (disposed) {
                        singleItem = null;
                        queue = null;
                        return;
                    }

                    if (error.get() != null) {
                        singleItem = null;
                        queue = null;
                        actual.onError(error.terminate());
                        return;
                    }

                    int os = otherState;
                    if (os == OTHER_STATE_HAS_VALUE) {
                        T v = singleItem;
                        singleItem = null;
                        otherState = OTHER_STATE_CONSUMED_OR_EMPTY;
                        os = OTHER_STATE_CONSUMED_OR_EMPTY;
                        actual.onNext(v);
                    }

                    boolean d = mainDone;
                    SimplePlainQueue<T> q = queue;
                    T v = q != null ? q.poll() : null;
                    boolean empty = v == null;

                    if (d && empty && os == OTHER_STATE_CONSUMED_OR_EMPTY) {
                        queue = null;
                        actual.onComplete();
                        return;
                    }

                    if (empty) {
                        break;
                    }

                    actual.onNext(v);
                }

                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        static final class OtherObserver<T> extends AtomicReference<Disposable>
        implements SingleObserver<T> {

            private static final long serialVersionUID = -2935427570954647017L;

            final MergeWithObserver<T> parent;

            OtherObserver(MergeWithObserver<T> parent) {
                this.parent = parent;
            }

            @Override
            public void onSubscribe(Disposable d) {
                DisposableHelper.setOnce(this, d);
            }

            @Override
            public void onSuccess(T t) {
                parent.otherSuccess(t);
            }

            @Override
            public void onError(Throwable e) {
                parent.otherError(e);
            }

        }
    }
}