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/**
 * Copyright 2014 Netflix, Inc.
 *
 * 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 rx.subjects;

import rx.Subscriber;
import rx.observers.SerializedObserver;

/**
 * Wraps a {@link Subject} so that it is safe to call its various {@code on} methods from different threads.
 * 
 * When you use an ordinary {@link Subject} as a {@link Subscriber}, you must take care not to call its
 * {@link Subscriber#onNext} method (or its other {@code on} methods) from multiple threads, as this could lead
 * to non-serialized calls, which violates the
 * Observable contract and creates an ambiguity in the resulting Subject.
 * 

 * To protect a {@code Subject} from this danger, you can convert it into a {@code SerializedSubject} with code
 * like the following:
 * 
{@code
 * mySafeSubject = new SerializedSubject( myUnsafeSubject );
 * }
 *
 * @param  the input value type
 * @param  the output value type
 */
public class SerializedSubject extends Subject {
    private final SerializedObserver observer;
    private final Subject actual;

    public SerializedSubject(final Subject actual) {
        super(new OnSubscribe() {

            @Override
            public void call(Subscriber child) {
                actual.unsafeSubscribe(child);
            }

        });
        this.actual = actual;
        this.observer = new SerializedObserver(actual);
    }

    @Override
    public void onCompleted() {
        observer.onCompleted();
    }

    @Override
    public void onError(Throwable e) {
        observer.onError(e);
    }

    @Override
    public void onNext(T t) {
        observer.onNext(t);
    }

    @Override
    public boolean hasObservers() {
        return actual.hasObservers();
    }
}