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.observable;

import io.reactivex.*;
import io.reactivex.annotations.Nullable;
import io.reactivex.functions.*;
import io.reactivex.internal.observers.BasicFuseableObserver;

public final class ObservableDistinctUntilChanged<T, K> extends AbstractObservableWithUpstream<T, T> {

    final Function<? super T, K> keySelector;

    final BiPredicate<? super K, ? super K> comparer;

    public ObservableDistinctUntilChanged(ObservableSource<T> source, Function<? super T, K> keySelector, BiPredicate<? super K, ? super K> comparer) {
        super(source);
        this.keySelector = keySelector;
        this.comparer = comparer;
    }

    @Override
    protected void subscribeActual(Observer<? super T> observer) {
        source.subscribe(new DistinctUntilChangedObserver<T, K>(observer, keySelector, comparer));
    }

    static final class DistinctUntilChangedObserver<T, K> extends BasicFuseableObserver<T, T> {

        final Function<? super T, K> keySelector;

        final BiPredicate<? super K, ? super K> comparer;

        K last;

        boolean hasValue;

        DistinctUntilChangedObserver(Observer<? super T> actual,
                Function<? super T, K> keySelector,
                BiPredicate<? super K, ? super K> comparer) {
            super(actual);
            this.keySelector = keySelector;
            this.comparer = comparer;
        }

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }
            if (sourceMode != NONE) {
                downstream.onNext(t);
                return;
            }

            K key;

            try {
                key = keySelector.apply(t);
                if (hasValue) {
                    boolean equal = comparer.test(last, key);
                    last = key;
                    if (equal) {
                        return;
                    }
                } else {
                    hasValue = true;
                    last = key;
                }
            } catch (Throwable ex) {
               fail(ex);
               return;
            }

            downstream.onNext(t);
        }

        @Override
        public int requestFusion(int mode) {
            return transitiveBoundaryFusion(mode);
        }

        @Nullable
        @Override
        public T poll() throws Exception {
            for (;;) {
                T v = qd.poll();
                if (v == null) {
                    return null;
                }
                K key = keySelector.apply(v);
                if (!hasValue) {
                    hasValue = true;
                    last = key;
                    return v;
                }

                if (!comparer.test(last, key)) {
                    last = key;
                    return v;
                }
                last = key;
            }
        }

    }
}