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 static org.junit.Assert.*;
  import static org.mockito.ArgumentMatchers.*;
  import static org.mockito.Mockito.*;
  
  import java.util.*;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.junit.Test;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.core.Observable;
  import io.reactivex.rxjava3.core.Observer;
  import io.reactivex.rxjava3.disposables.*;
  import io.reactivex.rxjava3.exceptions.TestException;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.observers.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  import io.reactivex.rxjava3.subjects.PublishSubject;
  import io.reactivex.rxjava3.testsupport.*;
  
  public class ObservableScanTest extends RxJavaTest {
  
      @Test
      public void scanIntegersWithInitialValue() {
          Observer<String> observer = TestHelper.mockObserver();
  
          Observable<Integer> o = Observable.just(1, 2, 3);
  
          Observable<String> m = o.scan("", new BiFunction<String, Integer, String>() {
  
              @Override
              public String apply(String s, Integer n) {
                  return s + n.toString();
              }
  
          });
          m.subscribe(observer);
  
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, times(1)).onNext("");
          verify(observer, times(1)).onNext("1");
          verify(observer, times(1)).onNext("12");
          verify(observer, times(1)).onNext("123");
          verify(observer, times(4)).onNext(anyString());
          verify(observer, times(1)).onComplete();
          verify(observer, never()).onError(any(Throwable.class));
      }
  
      @Test
      public void scanIntegersWithoutInitialValue() {
          Observer<Integer> observer = TestHelper.mockObserver();
  
          Observable<Integer> o = Observable.just(1, 2, 3);
  
          Observable<Integer> m = o.scan(new BiFunction<Integer, Integer, Integer>() {
  
              @Override
              public Integer apply(Integer t1, Integer t2) {
                  return t1 + t2;
              }
  
          });
          m.subscribe(observer);
  
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, never()).onNext(0);
          verify(observer, times(1)).onNext(1);
          verify(observer, times(1)).onNext(3);
          verify(observer, times(1)).onNext(6);
          verify(observer, times(3)).onNext(anyInt());
          verify(observer, times(1)).onComplete();
          verify(observer, never()).onError(any(Throwable.class));
      }
  
      @Test
      public void scanIntegersWithoutInitialValueAndOnlyOneValue() {
          Observer<Integer> observer = TestHelper.mockObserver();
  
          Observable<Integer> o = Observable.just(1);
  
          Observable<Integer> m = o.scan(new BiFunction<Integer, Integer, Integer>() {
  
              @Override
              public Integer apply(Integer t1, Integer t2) {
                  return t1 + t2;
              }
  
          });
          m.subscribe(observer);
  
          verify(observer, never()).onError(any(Throwable.class));
          verify(observer, never()).onNext(0);
          verify(observer, times(1)).onNext(1);
          verify(observer, times(1)).onNext(anyInt());
          verify(observer, times(1)).onComplete();
          verify(observer, never()).onError(any(Throwable.class));
      }
  
      @Test
      public void shouldNotEmitUntilAfterSubscription() {
          TestObserver<Integer> to = new TestObserver<>();
          Observable.range(1, 100).scan(0, new BiFunction<Integer, Integer, Integer>() {
  
              @Override
              public Integer apply(Integer t1, Integer t2) {
                  return t1 + t2;
              }
  
          }).filter(new Predicate<Integer>() {
  
              @Override
              public boolean test(Integer t1) {
                  // this will cause request(1) when 0 is emitted
                  return t1 > 0;
              }
  
          }).subscribe(to);
  
          assertEquals(100, to.values().size());
      }
  
      @Test
      public void noBackpressureWithInitialValue() {
          final AtomicInteger count = new AtomicInteger();
          Observable.range(1, 100)
                  .scan(0, new BiFunction<Integer, Integer, Integer>() {
  
                      @Override
                      public Integer apply(Integer t1, Integer t2) {
                          return t1 + t2;
                      }
  
                  })
                  .subscribe(new DefaultObserver<Integer>() {
  
                      @Override
                      public void onComplete() {
  
                      }
  
                      @Override
                      public void onError(Throwable e) {
                          fail(e.getMessage());
                          e.printStackTrace();
                      }
  
                      @Override
                      public void onNext(Integer t) {
                          count.incrementAndGet();
                      }
  
                  });
  
          // we only expect to receive 101 as we'll receive all 100 + the initial value
          assertEquals(101, count.get());
      }
  
      /**
       * This uses the public API collect which uses scan under the covers.
       */
      @Test
      public void seedFactory() {
          Observable<List<Integer>> o = Observable.range(1, 10)
                  .collect(new Supplier<List<Integer>>() {
  
                      @Override
                      public List<Integer> get() {
                          return new ArrayList<>();
                      }
  
                  }, new BiConsumer<List<Integer>, Integer>() {
  
                      @Override
                      public void accept(List<Integer> list, Integer t2) {
                          list.add(t2);
                      }
  
                  }).toObservable().takeLast(1);
  
          assertEquals(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), o.blockingSingle());
          assertEquals(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), o.blockingSingle());
      }
  
      @Test
      public void scanWithRequestOne() {
          Observable<Integer> o = Observable.just(1, 2).scan(0, new BiFunction<Integer, Integer, Integer>() {
  
              @Override
              public Integer apply(Integer t1, Integer t2) {
                  return t1 + t2;
              }
  
          }).take(1);
  
          TestObserverEx<Integer> observer = new TestObserverEx<>();
  
          o.subscribe(observer);
          observer.assertValue(0);
          observer.assertTerminated();
          observer.assertNoErrors();
      }
  
      @Test
      public void initialValueEmittedNoProducer() {
          PublishSubject<Integer> source = PublishSubject.create();
  
          TestObserver<Integer> to = new TestObserver<>();
  
          source.scan(0, new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer t1, Integer t2) {
                  return t1 + t2;
              }
          }).subscribe(to);
  
          to.assertNoErrors();
          to.assertNotComplete();
          to.assertValue(0);
      }
  
      @Test
      public void dispose() {
          TestHelper.checkDisposed(PublishSubject.create().scan(new BiFunction<Object, Object, Object>() {
              @Override
              public Object apply(Object a, Object b) throws Exception {
                  return a;
              }
          }));
  
          TestHelper.checkDisposed(PublishSubject.<Integer>create().scan(0, new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer a, Integer b) throws Exception {
                  return a + b;
              }
          }));
      }
  
      @Test
      public void doubleOnSubscribe() {
          TestHelper.checkDoubleOnSubscribeObservable(new Function<Observable<Object>, ObservableSource<Object>>() {
              @Override
              public ObservableSource<Object> apply(Observable<Object> o) throws Exception {
                  return o.scan(new BiFunction<Object, Object, Object>() {
                      @Override
                      public Object apply(Object a, Object b) throws Exception {
                          return a;
                      }
                  });
              }
          });
  
          TestHelper.checkDoubleOnSubscribeObservable(new Function<Observable<Object>, ObservableSource<Object>>() {
              @Override
              public ObservableSource<Object> apply(Observable<Object> o) throws Exception {
                  return o.scan(0, new BiFunction<Object, Object, Object>() {
                      @Override
                      public Object apply(Object a, Object b) throws Exception {
                          return a;
                      }
                  });
              }
          });
      }
  
      @Test
      public void error() {
          Observable.error(new TestException())
          .scan(new BiFunction<Object, Object, Object>() {
              @Override
              public Object apply(Object a, Object b) throws Exception {
                  return a;
              }
          })
          .test()
          .assertFailure(TestException.class);
      }
  
      @Test
      public void badSource() {
          TestHelper.checkBadSourceObservable(new Function<Observable<Object>, Object>() {
              @Override
              public Object apply(Observable<Object> o) throws Exception {
                  return o.scan(0, new BiFunction<Object, Object, Object>() {
                      @Override
                      public Object apply(Object a, Object b) throws Exception {
                          return a;
                      }
                  });
              }
          }, false, 1, 1, 0, 0);
      }
  
      @Test
      public void scanFunctionThrowsAndUpstreamErrorsDoesNotResultInTwoTerminalEvents() {
          final RuntimeException err = new RuntimeException();
          final RuntimeException err2 = new RuntimeException();
          final List<Throwable> list = new CopyOnWriteArrayList<>();
          final Consumer<Throwable> errorConsumer = new Consumer<Throwable>() {
              @Override
              public void accept(Throwable t) throws Exception {
                  list.add(t);
              }};
          try {
              RxJavaPlugins.setErrorHandler(errorConsumer);
              Observable.unsafeCreate(new ObservableSource<Integer>() {
                  @Override
                  public void subscribe(Observer<? super Integer> o) {
                      Disposable d = Disposable.empty();
                      o.onSubscribe(d);
                      o.onNext(1);
                      o.onNext(2);
                      o.onError(err2);
                  }})
              .scan(new BiFunction<Integer, Integer, Integer>() {
                  @Override
                  public Integer apply(Integer t1, Integer t2) throws Exception {
                      throw err;
                  }})
              .test()
              .assertError(err)
              .assertValue(1);
          } finally {
              RxJavaPlugins.reset();
          }
      }
  
      @Test
      public void scanFunctionThrowsAndUpstreamCompletesDoesNotResultInTwoTerminalEvents() {
          final RuntimeException err = new RuntimeException();
          Observable.unsafeCreate(new ObservableSource<Integer>() {
              @Override
              public void subscribe(Observer<? super Integer> o) {
                  Disposable d = Disposable.empty();
                  o.onSubscribe(d);
                  o.onNext(1);
                  o.onNext(2);
                  o.onComplete();
              }})
          .scan(new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer t1, Integer t2) throws Exception {
                  throw err;
              }})
          .test()
          .assertError(err)
          .assertValue(1);
      }
  
      @Test
      public void scanFunctionThrowsAndUpstreamEmitsOnNextResultsInScanFunctionBeingCalledOnlyOnce() {
          final RuntimeException err = new RuntimeException();
          final AtomicInteger count = new AtomicInteger();
          Observable.unsafeCreate(new ObservableSource<Integer>() {
              @Override
              public void subscribe(Observer<? super Integer> o) {
                  Disposable d = Disposable.empty();
                  o.onSubscribe(d);
                  o.onNext(1);
                  o.onNext(2);
                  o.onNext(3);
              }})
          .scan(new BiFunction<Integer, Integer, Integer>() {
              @Override
              public Integer apply(Integer t1, Integer t2) throws Exception {
                  count.incrementAndGet();
                  throw err;
              }})
          .test()
          .assertError(err)
          .assertValue(1);
          assertEquals(1, count.get());
      }
  }
  