/**
 * 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.flowable;

import java.util.Arrays;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicLong;

import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;

import io.reactivex.Flowable;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;

/**
 * Creates {@link Flowable} of a number of items followed by either an error or
 * completion. Cancellation has no effect on preventing emissions until the
 * currently outstanding requests have been met.
 * @param <T> the value type
 */
public final class Burst<T> extends Flowable<T> {

    private final List<T> items;
    private final Throwable error;

    private Burst(Throwable error, List<T> items) {
        if (items.isEmpty()) {
            throw new IllegalArgumentException("items cannot be empty");
        }
        for (T item : items) {
            if (item == null) {
                throw new IllegalArgumentException("items cannot include null");
            }
        }
        this.error = error;
        this.items = items;
    }

    @Override
    protected void subscribeActual(final Subscriber<? super T> subscriber) {
        subscriber.onSubscribe(new Subscription() {

            final Queue<T> q = new ConcurrentLinkedQueue<T>(items);
            final AtomicLong requested = new AtomicLong();
            volatile boolean cancelled;

            @Override
            public void request(long n) {
                if (cancelled) {
                    // required by reactive-streams-jvm 3.6
                    return;
                }
                if (SubscriptionHelper.validate(n)) {
                    // just for testing, don't care about perf
                    // so no attempt made to reduce volatile reads
                    if (BackpressureHelper.add(requested, n) == 0) {
                        if (q.isEmpty()) {
                            return;
                        }
                        while (!q.isEmpty() && requested.get() > 0) {
                            T item = q.poll();
                            requested.decrementAndGet();
                            subscriber.onNext(item);
                        }
                        if (q.isEmpty()) {
                            if (error != null) {
                                subscriber.onError(error);
                            } else {
                                subscriber.onComplete();
                            }
                        }
                    }
                }
            }

            @Override
            public void cancel() {
                cancelled = true;
            }
        });

    }

    @SuppressWarnings("unchecked")
    public static <T> Builder<T> item(T item) {
        return items(item);
    }

    public static <T> Builder<T> items(T... items) {
        return new Builder<T>(Arrays.asList(items));
    }

    public static final class Builder<T> {

        private final List<T> items;
        private Throwable error;

        private Builder(List<T> items) {
            this.items = items;
        }

        public Flowable<T> error(Throwable e) {
            this.error = e;
            return create();
        }

        public Flowable<T> create() {
            return new Burst<T>(error, items);
        }

    }

}
