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.flowable;

import java.util.NoSuchElementException;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableSingle<T> extends AbstractFlowableWithUpstream<T, T> {

    final T defaultValue;

    final boolean failOnEmpty;

    public FlowableSingle(Flowable<T> source, T defaultValue, boolean failOnEmpty) {
        super(source);
        this.defaultValue = defaultValue;
        this.failOnEmpty = failOnEmpty;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        source.subscribe(new SingleElementSubscriber<T>(s, defaultValue, failOnEmpty));
    }

    static final class SingleElementSubscriber<T> extends DeferredScalarSubscription<T>
    implements FlowableSubscriber<T> {

        private static final long serialVersionUID = -5526049321428043809L;

        final T defaultValue;

        final boolean failOnEmpty;

        Subscription upstream;

        boolean done;

        SingleElementSubscriber(Subscriber<? super T> actual, T defaultValue, boolean failOnEmpty) {
            super(actual);
            this.defaultValue = defaultValue;
            this.failOnEmpty = failOnEmpty;
        }

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

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }
            if (value != null) {
                done = true;
                upstream.cancel();
                downstream.onError(new IllegalArgumentException("Sequence contains more than one element!"));
                return;
            }
            value = t;
        }

        @Override
        public void onError(Throwable t) {
            if (done) {
                RxJavaPlugins.onError(t);
                return;
            }
            done = true;
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            T v = value;
            value = null;
            if (v == null) {
                v = defaultValue;
            }
            if (v == null) {
                if (failOnEmpty) {
                    downstream.onError(new NoSuchElementException());
                } else {
                    downstream.onComplete();
                }
            } else {
                complete(v);
            }
        }

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