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/**
 * 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.observable.internal.operators;

import java.util.NoSuchElementException;

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

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

    final ObservableSource source;

    final T defaultItem;

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

    // TODO fuse back to Observable

    @Override
    protected void subscribeActual(SingleObserver observer) {
        source.subscribe(new LastObserver(observer, defaultItem));
    }

    static final class LastObserver implements Observer, Disposable {

        final SingleObserver actual;

        final T defaultItem;

        Disposable s;

        T item;

        LastObserver(SingleObserver actual, T defaultItem) {
            this.actual = actual;
            this.defaultItem = defaultItem;
        }

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

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

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

                actual.onSubscribe(this);
            }
        }

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

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

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