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.flowable;

import java.util.concurrent.atomic.AtomicLong;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.plugins.RxJavaPlugins;

Limits both the total request amount and items received from the upstream.
History: 2.1.6 - experimental
Type parameters:
<T> – the source and output value type
Since:
2.2/**
 * Limits both the total request amount and items received from the upstream.
 * <p>History: 2.1.6 - experimental
 * @param <T> the source and output value type
 * @since 2.2
 */
public final class FlowableLimit<T> extends AbstractFlowableWithUpstream<T, T> {

    final long n;

    public FlowableLimit(Flowable<T> source, long n) {
        super(source);
        this.n = n;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        source.subscribe(new LimitSubscriber<T>(s, n));
    }

    static final class LimitSubscriber<T>
    extends AtomicLong
    implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = 2288246011222124525L;

        final Subscriber<? super T> downstream;

        long remaining;

        Subscription upstream;

        LimitSubscriber(Subscriber<? super T> actual, long remaining) {
            this.downstream = actual;
            this.remaining = remaining;
            lazySet(remaining);
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                if (remaining == 0L) {
                    s.cancel();
                    EmptySubscription.complete(downstream);
                } else {
                    this.upstream = s;
                    downstream.onSubscribe(this);
                }
            }
        }

        @Override
        public void onNext(T t) {
            long r = remaining;
            if (r > 0L) {
                remaining = --r;
                downstream.onNext(t);
                if (r == 0L) {
                    upstream.cancel();
                    downstream.onComplete();
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (remaining > 0L) {
                remaining = 0L;
                downstream.onError(t);
            } else {
                RxJavaPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            if (remaining > 0L) {
                remaining = 0L;
                downstream.onComplete();
            }
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                for (;;) {
                    long r = get();
                    if (r == 0L) {
                        break;
                    }
                    long toRequest;
                    if (r <= n) {
                        toRequest = r;
                    } else {
                        toRequest = n;
                    }
                    long u = r - toRequest;
                    if (compareAndSet(r, u)) {
                        upstream.request(toRequest);
                        break;
                    }
                }
            }
        }

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

    }
}