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.observable;
  
  import java.util.ArrayDeque;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  
  public final class ObservableTakeLast<T> extends AbstractObservableWithUpstream<T, T> {
      final int count;
  
      public ObservableTakeLast(ObservableSource<T> source, int count) {
          super(source);
          this.count = count;
      }
  
      @Override
      public void subscribeActual(Observer<? super T> t) {
          source.subscribe(new TakeLastObserver<>(t, count));
      }
  
      static final class TakeLastObserver<T> extends ArrayDeque<T> implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = 7240042530241604978L;
          final Observer<? super T> downstream;
          final int count;
  
          Disposable upstream;
  
          volatile boolean cancelled;
  
          TakeLastObserver(Observer<? super T> actual, int count) {
              this.downstream = actual;
              this.count = count;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @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() {
              Observer<? super T> a = downstream;
              for (;;) {
                  if (cancelled) {
                      return;
                  }
                  T v = poll();
                  if (v == null) {
                      a.onComplete();
                      return;
                  }
                  a.onNext(v);
              }
          }
  
          @Override
          public void dispose() {
              if (!cancelled) {
                  cancelled = true;
                  upstream.dispose();
              }
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
      }
  }
  