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.maybe;

import java.util.NoSuchElementException;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.fuseable.HasUpstreamMaybeSource;

Wraps a MaybeSource and exposes its onSuccess and onError signals and signals
NoSuchElementException for onComplete.
Type parameters:
<T> – the value type/**
 * Wraps a MaybeSource and exposes its onSuccess and onError signals and signals
 * NoSuchElementException for onComplete.
 *
 * @param <T> the value type
 */
public final class MaybeToSingle<T> extends Single<T> implements HasUpstreamMaybeSource<T> {

    final MaybeSource<T> source;
    final T defaultValue;

    public MaybeToSingle(MaybeSource<T> source, T defaultValue) {
        this.source = source;
        this.defaultValue = defaultValue;
    }

    @Override
    public MaybeSource<T> source() {
        return source;
    }

    @Override
    protected void subscribeActual(SingleObserver<? super T> observer) {
        source.subscribe(new ToSingleMaybeSubscriber<T>(observer, defaultValue));
    }

    static final class ToSingleMaybeSubscriber<T> implements MaybeObserver<T>, Disposable {
        final SingleObserver<? super T> downstream;
        final T defaultValue;

        Disposable upstream;

        ToSingleMaybeSubscriber(SingleObserver<? super T> actual, T defaultValue) {
            this.downstream = actual;
            this.defaultValue = defaultValue;
        }

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

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

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

                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onSuccess(T value) {
            upstream = DisposableHelper.DISPOSED;
            downstream.onSuccess(value);
        }

        @Override
        public void onError(Throwable e) {
            upstream = DisposableHelper.DISPOSED;
            downstream.onError(e);
        }

        @Override
        public void onComplete() {
            upstream = DisposableHelper.DISPOSED;
            if (defaultValue != null) {
                downstream.onSuccess(defaultValue);
            } else {
                downstream.onError(new NoSuchElementException("The MaybeSource is empty"));
            }
        }
    }
}