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.maybe;

import java.util.concurrent.atomic.*;

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

Consumes the source once and replays its signal to any current or future MaybeObservers.
Type parameters:
<T> – the value type/**
 * Consumes the source once and replays its signal to any current or future MaybeObservers.
 *
 * @param <T> the value type
 */
public final class MaybeCache<T> extends Maybe<T> implements MaybeObserver<T> {

    @SuppressWarnings("rawtypes")
    static final CacheDisposable[] EMPTY = new CacheDisposable[0];

    @SuppressWarnings("rawtypes")
    static final CacheDisposable[] TERMINATED = new CacheDisposable[0];

    final AtomicReference<MaybeSource<T>> source;

    final AtomicReference<CacheDisposable<T>[]> observers;

    T value;

    Throwable error;

    @SuppressWarnings("unchecked")
    public MaybeCache(MaybeSource<T> source) {
        this.source = new AtomicReference<MaybeSource<T>>(source);
        this.observers = new AtomicReference<CacheDisposable<T>[]>(EMPTY);
    }

    @Override
    protected void subscribeActual(MaybeObserver<? super T> observer) {
        CacheDisposable<T> parent = new CacheDisposable<T>(observer, this);
        observer.onSubscribe(parent);

        if (add(parent)) {
            if (parent.isDisposed()) {
                remove(parent);
                return;
            }
        } else {
            if (!parent.isDisposed()) {
                Throwable ex = error;
                if (ex != null) {
                    observer.onError(ex);
                } else {
                    T v = value;
                    if (v != null) {
                        observer.onSuccess(v);
                    } else {
                        observer.onComplete();
                    }
                }
            }
            return;
        }

        MaybeSource<T> src = source.getAndSet(null);
        if (src != null) {
            src.subscribe(this);
        }
    }

    @Override
    public void onSubscribe(Disposable d) {
        // deliberately ignored
    }

    @SuppressWarnings("unchecked")
    @Override
    public void onSuccess(T value) {
        this.value = value;
        for (CacheDisposable<T> inner : observers.getAndSet(TERMINATED)) {
            if (!inner.isDisposed()) {
                inner.downstream.onSuccess(value);
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void onError(Throwable e) {
        this.error = e;
        for (CacheDisposable<T> inner : observers.getAndSet(TERMINATED)) {
            if (!inner.isDisposed()) {
                inner.downstream.onError(e);
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void onComplete() {
        for (CacheDisposable<T> inner : observers.getAndSet(TERMINATED)) {
            if (!inner.isDisposed()) {
                inner.downstream.onComplete();
            }
        }
    }

    boolean add(CacheDisposable<T> inner) {
        for (;;) {
            CacheDisposable<T>[] a = observers.get();
            if (a == TERMINATED) {
                return false;
            }
            int n = a.length;

            @SuppressWarnings("unchecked")
            CacheDisposable<T>[] b = new CacheDisposable[n + 1];
            System.arraycopy(a, 0, b, 0, n);
            b[n] = inner;
            if (observers.compareAndSet(a, b)) {
                return true;
            }
        }
    }

    @SuppressWarnings("unchecked")
    void remove(CacheDisposable<T> inner) {
        for (;;) {
            CacheDisposable<T>[] 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;
            }

            CacheDisposable<T>[] b;
            if (n == 1) {
                b = EMPTY;
            } else {
                b = new CacheDisposable[n - 1];
                System.arraycopy(a, 0, b, 0, j);
                System.arraycopy(a, j + 1, b, j, n - j - 1);
            }
            if (observers.compareAndSet(a, b)) {
                return;
            }
        }
    }

    static final class CacheDisposable<T>
    extends AtomicReference<MaybeCache<T>>
    implements Disposable {

        private static final long serialVersionUID = -5791853038359966195L;

        final MaybeObserver<? super T> downstream;

        CacheDisposable(MaybeObserver<? super T> actual, MaybeCache<T> parent) {
            super(parent);
            this.downstream = actual;
        }

        @Override
        public void dispose() {
            MaybeCache<T> mc = getAndSet(null);
            if (mc != null) {
                mc.remove(this);
            }
        }

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