/**

* 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.operators;

import java.util.concurrent.ConcurrentLinkedQueue;

import java.util.concurrent.atomic.AtomicInteger;

import rx.Observable;

import rx.Observer;

import rx.Operator;

import rx.subscriptions.CompositeSubscription;

import rx.util.functions.Func1;

/**

* Flattens a list of Observables into one Observable sequence, without any transformation.

* <p>

* <img width="640" src="https://github.com/Netflix/RxJava/wiki/images/rx-operators/merge.png">

* <p>

* You can combine the items emitted by multiple Observables so that they act like a single

* Observable, by using the merge operation.

*/

public final class OperatorMerge<T> implements Func1<Operator<? super T>, Operator<? extends Observable<? extends T>>> {

private final int maxConcurrent;

public OperatorMerge() {

maxConcurrent = Integer.MAX_VALUE;

}

public OperatorMerge(int maxConcurrent) {

if (maxConcurrent <= 0) {

throw new IllegalArgumentException("maxConcurrent must be positive");

}

this.maxConcurrent = maxConcurrent;

}

@Override

public Operator<? extends Observable<? extends T>> call(final Operator<? super T> outerOperation) {

final AtomicInteger completionCounter = new AtomicInteger(1);

final AtomicInteger concurrentCounter = new AtomicInteger(1);

// Concurrent* since we'll be accessing them from the inner Observers which can be on other threads

final ConcurrentLinkedQueue<Observable<? extends T>> pending = new ConcurrentLinkedQueue<Observable<? extends T>>();

final Observer<T> o = new SynchronizedObserver<T>(outerOperation);

return new Operator<Observable<? extends T>>(outerOperation) {

@Override

public void onCompleted() {

complete();

}

@Override

public void onError(Throwable e) {

o.onError(e);

}

@Override

public void onNext(Observable<? extends T> innerObservable) {

// track so we send onComplete only when all have finished

completionCounter.incrementAndGet();

// check concurrency

if (concurrentCounter.incrementAndGet() > maxConcurrent) {

pending.add(innerObservable);

concurrentCounter.decrementAndGet();

} else {

// we are able to proceed

CompositeSubscription innerSubscription = new CompositeSubscription();

outerOperation.add(innerSubscription);

innerObservable.subscribe(Operator.create(new InnerObserver(), innerSubscription));

}

}

private void complete() {

if (completionCounter.decrementAndGet() == 0) {

o.onCompleted();

return;

} else {

// not all are completed and some may still need to run

concurrentCounter.decrementAndGet();

}

// do work-stealing on whatever thread we're on and subscribe to pending observables

if (concurrentCounter.incrementAndGet() > maxConcurrent) {

// still not space to run

concurrentCounter.decrementAndGet();

} else {

// we can run

Observable<? extends T> outstandingObservable = pending.poll();

if (outstandingObservable != null) {

CompositeSubscription innerSubscription = new CompositeSubscription();

outerOperation.add(innerSubscription);

outstandingObservable.subscribe(Operator.create(new InnerObserver(), innerSubscription));

}

}

}

final class InnerObserver implements Observer<T> {

@Override

public void onCompleted() {

complete();

}

@Override

public void onError(Throwable e) {

o.onError(e);

}

@Override

public void onNext(T a) {

o.onNext(a);

}

};

};

}

}