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.single;

import java.util.concurrent.atomic.*;

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

public final class SingleCache<T> extends Single<T> implements SingleObserver<T> {

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

    final SingleSource<? extends T> source;

    final AtomicInteger wip;

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

    T value;

    Throwable error;

    @SuppressWarnings("unchecked")
    public SingleCache(SingleSource<? extends T> source) {
        this.source = source;
        this.wip = new AtomicInteger();
        this.observers = new AtomicReference<CacheDisposable<T>[]>(EMPTY);
    }

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

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

        if (wip.getAndIncrement() == 0) {
            source.subscribe(this);
        }
    }

    boolean add(CacheDisposable<T> observer) {
        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] = observer;
            if (observers.compareAndSet(a, b)) {
                return true;
            }
        }
    }

    @SuppressWarnings("unchecked")
    void remove(CacheDisposable<T> observer) {
        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] == observer) {
                    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;
            }
        }
    }

    @Override
    public void onSubscribe(Disposable d) {
        // not supported by this operator
    }

    @SuppressWarnings("unchecked")
    @Override
    public void onSuccess(T value) {
        this.value = value;

        for (CacheDisposable<T> d : observers.getAndSet(TERMINATED)) {
            if (!d.isDisposed()) {
                d.downstream.onSuccess(value);
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void onError(Throwable e) {
        this.error = e;

        for (CacheDisposable<T> d : observers.getAndSet(TERMINATED)) {
            if (!d.isDisposed()) {
                d.downstream.onError(e);
            }
        }
    }

    static final class CacheDisposable<T>
    extends AtomicBoolean
    implements Disposable {

        private static final long serialVersionUID = 7514387411091976596L;

        final SingleObserver<? super T> downstream;

        final SingleCache<T> parent;

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

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

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