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

import java.util.NoSuchElementException;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableElementAtSingle<T> extends Single<T> implements FuseToObservable<T> {
    final ObservableSource<T> source;
    final long index;
    final T defaultValue;

    public ObservableElementAtSingle(ObservableSource<T> source, long index, T defaultValue) {
        this.source = source;
        this.index = index;
        this.defaultValue = defaultValue;
    }

    @Override
    public void subscribeActual(SingleObserver<? super T> t) {
        source.subscribe(new ElementAtObserver<T>(t, index, defaultValue));
    }

    @Override
    public Observable<T> fuseToObservable() {
        return RxJavaPlugins.onAssembly(new ObservableElementAt<T>(source, index, defaultValue, true));
    }

    static final class ElementAtObserver<T> implements Observer<T>, Disposable {
        final SingleObserver<? super T> downstream;
        final long index;
        final T defaultValue;

        Disposable upstream;

        long count;

        boolean done;

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

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

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

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

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }
            long c = count;
            if (c == index) {
                done = true;
                upstream.dispose();
                downstream.onSuccess(t);
                return;
            }
            count = c + 1;
        }

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

        @Override
        public void onComplete() {
            if (!done) {
                done = true;

                T v = defaultValue;

                if (v != null) {
                    downstream.onSuccess(v);
                } else {
                    downstream.onError(new NoSuchElementException());
                }
            }
        }
    }
}