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;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableElementAt<T> extends AbstractObservableWithUpstream<T, T> {
    final long index;
    final T defaultValue;
    final boolean errorOnFewer;

    public ObservableElementAt(ObservableSource<T> source, long index, T defaultValue, boolean errorOnFewer) {
        super(source);
        this.index = index;
        this.defaultValue = defaultValue;
        this.errorOnFewer = errorOnFewer;
    }

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

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

        Disposable upstream;

        long count;

        boolean done;

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

        @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.onNext(t);
                downstream.onComplete();
                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 && errorOnFewer) {
                    downstream.onError(new NoSuchElementException());
                } else {
                    if (v != null) {
                        downstream.onNext(v);
                    }
                    downstream.onComplete();
                }
            }
        }
    }
}