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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.internal.util;

import rx.Scheduler;
import rx.Scheduler.Worker;
import rx.Single;
import rx.SingleSubscriber;
import rx.Subscriber;
import rx.functions.Action0;
import rx.functions.Func1;
import rx.internal.schedulers.EventLoopsScheduler;

public final class ScalarSynchronousSingle extends Single {

    final T value;

    public static  ScalarSynchronousSingle create(T t) {
        return new ScalarSynchronousSingle(t);
    }

    protected ScalarSynchronousSingle(final T t) {
        super(new OnSubscribe() {

            @Override
            public void call(SingleSubscriber te) {
                te.onSuccess(t);
            }

        });
        this.value = t;
    }

    public T get() {
        return value;
    }

    /**
     * Customized observeOn/subscribeOn implementation which emits the scalar
     * value directly or with less overhead on the specified scheduler.
     *
     * @param scheduler the target scheduler
     * @return the new observable
     */
    public Single scalarScheduleOn(Scheduler scheduler) {
        if (scheduler instanceof EventLoopsScheduler) {
            EventLoopsScheduler es = (EventLoopsScheduler) scheduler;
            return create(new DirectScheduledEmission(es, value));
        }
        return create(new NormalScheduledEmission(scheduler, value));
    }

    /**
     * Optimized observeOn for scalar value observed on the EventLoopsScheduler.
     */
    static final class DirectScheduledEmission implements OnSubscribe {
        private final EventLoopsScheduler es;
        private final T value;

        DirectScheduledEmission(EventLoopsScheduler es, T value) {
            this.es = es;
            this.value = value;
        }

        @Override
        public void call(SingleSubscriber singleSubscriber) {
            singleSubscriber.add(es.scheduleDirect(new ScalarSynchronousSingleAction(singleSubscriber, value)));
        }
    }

    /**
     * Emits a scalar value on a general scheduler.
     */
    static final class NormalScheduledEmission implements OnSubscribe {
        private final Scheduler scheduler;
        private final T value;

        NormalScheduledEmission(Scheduler scheduler, T value) {
            this.scheduler = scheduler;
            this.value = value;
        }

        @Override
        public void call(SingleSubscriber singleSubscriber) {
            Worker worker = scheduler.createWorker();
            singleSubscriber.add(worker);
            worker.schedule(new ScalarSynchronousSingleAction(singleSubscriber, value));
        }
    }

    /**
     * Action that emits a single value when called.
     */
    static final class ScalarSynchronousSingleAction implements Action0 {
        private final SingleSubscriber subscriber;
        private final T value;

        ScalarSynchronousSingleAction(SingleSubscriber subscriber,
                                      T value) {
            this.subscriber = subscriber;
            this.value = value;
        }

        @Override
        public void call() {
            try {
                subscriber.onSuccess(value);
            } catch (Throwable t) {
                subscriber.onError(t);
            }
        }
    }

    public  Single scalarFlatMap(final Func1> func) {
        return create(new OnSubscribe() {
            @Override
            public void call(final SingleSubscriber child) {

                Single o = func.call(value);
                if (o instanceof ScalarSynchronousSingle) {
                    child.onSuccess(((ScalarSynchronousSingle) o).value);
                } else {
                    Subscriber subscriber = new Subscriber() {
                        @Override
                        public void onCompleted() {
                            // deliberately ignored
                        }

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

                        @Override
                        public void onNext(R r) {
                            child.onSuccess(r);
                        }
                    };
                    child.add(subscriber);
                    o.unsafeSubscribe(subscriber);
                }
            }
        });
    }
}