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.subscriptions;

import io.reactivex.annotations.Nullable;
import org.reactivestreams.Subscriber;

import io.reactivex.internal.fuseable.QueueSubscription;

An empty subscription that does nothing other than validates the request amount.
/**
 * An empty subscription that does nothing other than validates the request amount.
 */
public enum EmptySubscription implements QueueSubscription<Object> {
    
A singleton, stateless instance. /** A singleton, stateless instance. */
    INSTANCE;

    @Override
    public void request(long n) {
        SubscriptionHelper.validate(n);
    }

    @Override
    public void cancel() {
        // no-op
    }

    @Override
    public String toString() {
        return "EmptySubscription";
    }

    
Sets the empty subscription instance on the subscriber and then
calls onError with the supplied error.
Make sure this is only called if the subscriber hasn't received a
subscription already (there is no way of telling this).
Params:
e – the error to deliver to the subscriber
s – the target subscriber/**
     * Sets the empty subscription instance on the subscriber and then
     * calls onError with the supplied error.
     *
     * <p>Make sure this is only called if the subscriber hasn't received a
     * subscription already (there is no way of telling this).
     *
     * @param e the error to deliver to the subscriber
     * @param s the target subscriber
     */
    public static void error(Throwable e, Subscriber<?> s) {
        s.onSubscribe(INSTANCE);
        s.onError(e);
    }

    
Sets the empty subscription instance on the subscriber and then
calls onComplete.
Make sure this is only called if the subscriber hasn't received a
subscription already (there is no way of telling this).
Params:
s – the target subscriber/**
     * Sets the empty subscription instance on the subscriber and then
     * calls onComplete.
     *
     * <p>Make sure this is only called if the subscriber hasn't received a
     * subscription already (there is no way of telling this).
     *
     * @param s the target subscriber
     */
    public static void complete(Subscriber<?> s) {
        s.onSubscribe(INSTANCE);
        s.onComplete();
    }

    @Nullable
    @Override
    public Object poll() {
        return null; // always empty
    }

    @Override
    public boolean isEmpty() {
        return true;
    }

    @Override
    public void clear() {
        // nothing to do
    }

    @Override
    public int requestFusion(int mode) {
        return mode & ASYNC; // accept async mode: an onComplete or onError will be signalled after anyway
    }

    @Override
    public boolean offer(Object value) {
        throw new UnsupportedOperationException("Should not be called!");
    }

    @Override
    public boolean offer(Object v1, Object v2) {
        throw new UnsupportedOperationException("Should not be called!");
    }
}