code: /*
   * 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.rxjava3.internal.operators.flowable;
  
  import java.util.ArrayDeque;
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.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<>(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 (isEmpty()) {
                              a.onComplete();
                              return;
                          }
                          if (e != 0L) {
                              r = BackpressureHelper.produced(requested, e);
                          }
                      }
                  } while (wip.decrementAndGet() != 0);
              }
          }
      }
  }
  