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.NoSuchElementException;

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

Consumes the source ObservableSource and emits its last item, the defaultItem
if empty or a NoSuchElementException if even the defaultItem is null.
Type parameters:
<T> – the value type/**
 * Consumes the source ObservableSource and emits its last item, the defaultItem
 * if empty or a NoSuchElementException if even the defaultItem is null.
 * 
 * @param <T> the value type
 */
public final class ObservableLastSingle<T> extends Single<T> {

    final ObservableSource<T> source;

    final T defaultItem;

    public ObservableLastSingle(ObservableSource<T> source, T defaultItem) {
        this.source = source;
        this.defaultItem = defaultItem;
    }

    // TODO fuse back to Observable

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

    static final class LastObserver<T> implements Observer<T>, Disposable {

        final SingleObserver<? super T> downstream;

        final T defaultItem;

        Disposable upstream;

        T item;

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

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

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

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

                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onNext(T t) {
            item = t;
        }

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

        @Override
        public void onComplete() {
            upstream = DisposableHelper.DISPOSED;
            T v = item;
            if (v != null) {
                item = null;
                downstream.onSuccess(v);
            } else {
                v = defaultItem;
                if (v != null) {
                    downstream.onSuccess(v);
                } else {
                    downstream.onError(new NoSuchElementException());
                }
            }
        }
    }
}