/*
 * 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.rxjava4.internal.operators.flowable;

import static java.util.concurrent.Flow.*;

import io.reactivex.rxjava4.core.*;
import io.reactivex.rxjava4.internal.subscriptions.SubscriptionArbiter;

public final class FlowableSwitchIfEmpty<T> extends AbstractFlowableWithUpstream<T, T> {
    final Publisher<? extends T> other;
    public FlowableSwitchIfEmpty(Flowable<T> source, Publisher<? extends T> other) {
        super(source);
        this.other = other;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        SwitchIfEmptySubscriber<T> parent = new SwitchIfEmptySubscriber<>(s, other);
        s.onSubscribe(parent.arbiter);
        source.subscribe(parent);
    }

    static final class SwitchIfEmptySubscriber<T> implements FlowableSubscriber<T> {
        final Subscriber<? super T> downstream;
        final Publisher<? extends T> other;
        final SubscriptionArbiter arbiter;

        boolean empty;

        SwitchIfEmptySubscriber(Subscriber<? super T> actual, Publisher<? extends T> other) {
            this.downstream = actual;
            this.other = other;
            this.empty = true;
            this.arbiter = new SubscriptionArbiter(false);
        }

        @Override
        public void onSubscribe(Subscription s) {
            arbiter.setSubscription(s);
        }

        @Override
        public void onNext(T t) {
            if (empty) {
                empty = false;
            }
            downstream.onNext(t);
        }

        @Override
        public void onError(Throwable t) {
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            if (empty) {
                empty = false;
                other.subscribe(this);
            } else {
                downstream.onComplete();
            }
        }
    }
}
