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.completable;

import java.util.concurrent.atomic.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;

Consume the upstream source exactly once and cache its terminal event.
History: 2.0.4 - experimental
Since:
2.1/**
 * Consume the upstream source exactly once and cache its terminal event.
 * <p>History: 2.0.4 - experimental
 * @since 2.1
 */
public final class CompletableCache extends Completable implements CompletableObserver {

    static final InnerCompletableCache[] EMPTY = new InnerCompletableCache[0];

    static final InnerCompletableCache[] TERMINATED = new InnerCompletableCache[0];

    final CompletableSource source;

    final AtomicReference<InnerCompletableCache[]> observers;

    final AtomicBoolean once;

    Throwable error;

    public CompletableCache(CompletableSource source) {
        this.source = source;
        this.observers = new AtomicReference<InnerCompletableCache[]>(EMPTY);
        this.once = new AtomicBoolean();
    }

    @Override
    protected void subscribeActual(CompletableObserver observer) {
        InnerCompletableCache inner = new InnerCompletableCache(observer);
        observer.onSubscribe(inner);

        if (add(inner)) {
            if (inner.isDisposed()) {
                remove(inner);
            }

            if (once.compareAndSet(false, true)) {
                source.subscribe(this);
            }
        } else {
            Throwable ex = error;
            if (ex != null) {
                observer.onError(ex);
            } else {
                observer.onComplete();
            }
        }
    }

    @Override
    public void onSubscribe(Disposable d) {
        // not used
    }

    @Override
    public void onError(Throwable e) {
        error = e;
        for (InnerCompletableCache inner : observers.getAndSet(TERMINATED)) {
            if (!inner.get()) {
                inner.downstream.onError(e);
            }
        }
    }

    @Override
    public void onComplete() {
        for (InnerCompletableCache inner : observers.getAndSet(TERMINATED)) {
            if (!inner.get()) {
                inner.downstream.onComplete();
            }
        }
    }

    boolean add(InnerCompletableCache inner) {
        for (;;) {
            InnerCompletableCache[] a = observers.get();
            if (a == TERMINATED) {
                return false;
            }
            int n = a.length;
            InnerCompletableCache[] b = new InnerCompletableCache[n + 1];
            System.arraycopy(a, 0, b, 0, n);
            b[n] = inner;
            if (observers.compareAndSet(a, b)) {
                return true;
            }
        }
    }

    void remove(InnerCompletableCache inner) {
        for (;;) {
            InnerCompletableCache[] a = observers.get();
            int n = a.length;
            if (n == 0) {
                return;
            }

            int j = -1;

            for (int i = 0; i < n; i++) {
                if (a[i] == inner) {
                    j = i;
                    break;
                }
            }

            if (j < 0) {
                return;
            }

            InnerCompletableCache[] b;

            if (n == 1) {
                b = EMPTY;
            } else {
                b = new InnerCompletableCache[n - 1];
                System.arraycopy(a, 0, b, 0, j);
                System.arraycopy(a, j + 1, b, j, n - j - 1);
            }

            if (observers.compareAndSet(a, b)) {
                break;
            }
        }
    }

    final class InnerCompletableCache
    extends AtomicBoolean
    implements Disposable {

        private static final long serialVersionUID = 8943152917179642732L;

        final CompletableObserver downstream;

        InnerCompletableCache(CompletableObserver downstream) {
            this.downstream = downstream;
        }

        @Override
        public boolean isDisposed() {
            return get();
        }

        @Override
        public void dispose() {
            if (compareAndSet(false, true)) {
                remove(this);
            }
        }
    }
}