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.ArrayDeque;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;

public final class FlowableTakeLast<T> extends AbstractFlowableWithUpstream<T, T> {
    final int count;

    public FlowableTakeLast(Flowable<T> source, int count) {
        super(source);
        this.count = count;
    }

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

    static final class TakeLastSubscriber<T> extends ArrayDeque<T> implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = 7240042530241604978L;
        final Subscriber<? super T> downstream;
        final int count;

        Subscription upstream;
        volatile boolean done;
        volatile boolean cancelled;

        final AtomicLong requested = new AtomicLong();

        final AtomicInteger wip = new AtomicInteger();

        TakeLastSubscriber(Subscriber<? super T> actual, int count) {
            this.downstream = actual;
            this.count = count;
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;
                downstream.onSubscribe(this);
                s.request(Long.MAX_VALUE);
            }
        }

        @Override
        public void onNext(T t) {
            if (count == size()) {
                poll();
            }
            offer(t);
        }

        @Override
        public void onError(Throwable t) {
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            done = true;
            drain();
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
                drain();
            }
        }

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

        void drain() {
            if (wip.getAndIncrement() == 0) {
                Subscriber<? super T> a = downstream;
                long r = requested.get();
                do {
                    if (cancelled) {
                        return;
                    }
                    if (done) {
                        long e = 0L;

                        while (e != r) {
                            if (cancelled) {
                                return;
                            }
                            T v = poll();
                            if (v == null) {
                                a.onComplete();
                                return;
                            }
                            a.onNext(v);
                            e++;
                        }
                        if (e != 0L && r != Long.MAX_VALUE) {
                            r = requested.addAndGet(-e);
                        }
                    }
                } while (wip.decrementAndGet() != 0);
            }
        }
    }
}