/*
 * Copyright 2002-2019 the original author or authors.
 *
 * 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
 *
 *      https://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 org.springframework.http.server.reactive;

import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import org.junit.jupiter.api.Test;
import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.core.publisher.BaseSubscriber;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.publisher.Signal;
import reactor.test.StepVerifier;

import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.LeakAwareDataBufferFactory;

import static org.assertj.core.api.Assertions.assertThat;

/**
 * @author Rossen Stoyanchev
 * @author Stephane Maldini
 */
public class ChannelSendOperatorTests {

	private final OneByOneAsyncWriter writer = new OneByOneAsyncWriter();


	@Test
	public void errorBeforeFirstItem() throws Exception {
		IllegalStateException error = new IllegalStateException("boo");
		Mono<Void> completion = Mono.<String>error(error).as(this::sendOperator);
		Signal<Void> signal = completion.materialize().block();

		assertThat(signal).isNotNull();
		assertThat(signal.getThrowable()).as("Unexpected signal: " + signal).isSameAs(error);
	}

	@Test
	public void completionBeforeFirstItem() throws Exception {
		Mono<Void> completion = Flux.<String>empty().as(this::sendOperator);
		Signal<Void> signal = completion.materialize().block();

		assertThat(signal).isNotNull();
		assertThat(signal.isOnComplete()).as("Unexpected signal: " + signal).isTrue();

		assertThat(this.writer.items.size()).isEqualTo(0);
		assertThat(this.writer.completed).isTrue();
	}

	@Test
	public void writeOneItem() throws Exception {
		Mono<Void> completion = Flux.just("one").as(this::sendOperator);
		Signal<Void> signal = completion.materialize().block();

		assertThat(signal).isNotNull();
		assertThat(signal.isOnComplete()).as("Unexpected signal: " + signal).isTrue();

		assertThat(this.writer.items.size()).isEqualTo(1);
		assertThat(this.writer.items.get(0)).isEqualTo("one");
		assertThat(this.writer.completed).isTrue();
	}


	@Test
	public void writeMultipleItems() {
		List<String> items = Arrays.asList("one", "two", "three");
		Mono<Void> completion = Flux.fromIterable(items).as(this::sendOperator);
		Signal<Void> signal = completion.materialize().block();

		assertThat(signal).isNotNull();
		assertThat(signal.isOnComplete()).as("Unexpected signal: " + signal).isTrue();

		assertThat(this.writer.items.size()).isEqualTo(3);
		assertThat(this.writer.items.get(0)).isEqualTo("one");
		assertThat(this.writer.items.get(1)).isEqualTo("two");
		assertThat(this.writer.items.get(2)).isEqualTo("three");
		assertThat(this.writer.completed).isTrue();
	}

	@Test
	public void errorAfterMultipleItems() {
		IllegalStateException error = new IllegalStateException("boo");
		Flux<String> publisher = Flux.generate(() -> 0, (idx , subscriber) -> {
			int i = ++idx;
			subscriber.next(String.valueOf(i));
			if (i == 3) {
				subscriber.error(error);
			}
			return i;
		});
		Mono<Void> completion = publisher.as(this::sendOperator);
		Signal<Void> signal = completion.materialize().block();

		assertThat(signal).isNotNull();
		assertThat(signal.getThrowable()).as("Unexpected signal: " + signal).isSameAs(error);

		assertThat(this.writer.items.size()).isEqualTo(3);
		assertThat(this.writer.items.get(0)).isEqualTo("1");
		assertThat(this.writer.items.get(1)).isEqualTo("2");
		assertThat(this.writer.items.get(2)).isEqualTo("3");
		assertThat(this.writer.error).isSameAs(error);
	}

	@Test // gh-22720
	public void cancelWhileItemCached() {
		LeakAwareDataBufferFactory bufferFactory = new LeakAwareDataBufferFactory();

		ChannelSendOperator<DataBuffer> operator = new ChannelSendOperator<>(
				Mono.fromCallable(() -> {
					DataBuffer dataBuffer = bufferFactory.allocateBuffer();
					dataBuffer.write("foo", StandardCharsets.UTF_8);
					return dataBuffer;
				}),
				publisher -> {
					ZeroDemandSubscriber subscriber = new ZeroDemandSubscriber();
					publisher.subscribe(subscriber);
					return Mono.never();
				});

		BaseSubscriber<Void> subscriber = new BaseSubscriber<Void>() {};
		operator.subscribe(subscriber);
		subscriber.cancel();

		bufferFactory.checkForLeaks();
	}

	@Test // gh-22720
	public void errorFromWriteSourceWhileItemCached() {

		// 1. First item received
		// 2. writeFunction applied and writeCompletionBarrier subscribed to it
		// 3. Write Publisher fails right after that and before request(n) from server

		LeakAwareDataBufferFactory bufferFactory = new LeakAwareDataBufferFactory();
		ZeroDemandSubscriber writeSubscriber = new ZeroDemandSubscriber();

		ChannelSendOperator<DataBuffer> operator = new ChannelSendOperator<>(
				Flux.create(sink -> {
					DataBuffer dataBuffer = bufferFactory.allocateBuffer();
					dataBuffer.write("foo", StandardCharsets.UTF_8);
					sink.next(dataBuffer);
					sink.error(new IllegalStateException("err"));
				}),
				publisher -> {
					publisher.subscribe(writeSubscriber);
					return Mono.never();
				});


		operator.subscribe(new BaseSubscriber<Void>() {});
		try {
			writeSubscriber.signalDemand(1);  // Let cached signals ("foo" and error) be published..
		}
		catch (Throwable ex) {
			assertThat(ex.getCause()).isNotNull();
			assertThat(ex.getCause().getMessage()).isEqualTo("err");
		}

		bufferFactory.checkForLeaks();
	}

	@Test // gh-22720
	public void errorFromWriteFunctionWhileItemCached() {

		// 1. First item received
		// 2. writeFunction applied and writeCompletionBarrier subscribed to it
		// 3. writeFunction fails, e.g. to flush status and headers, before request(n) from server

		LeakAwareDataBufferFactory bufferFactory = new LeakAwareDataBufferFactory();

		ChannelSendOperator<DataBuffer> operator = new ChannelSendOperator<>(
				Flux.create(sink -> {
					DataBuffer dataBuffer = bufferFactory.allocateBuffer();
					dataBuffer.write("foo", StandardCharsets.UTF_8);
					sink.next(dataBuffer);
				}),
				publisher -> {
					publisher.subscribe(new ZeroDemandSubscriber());
					return Mono.error(new IllegalStateException("err"));
				});

		StepVerifier.create(operator).expectErrorMessage("err").verify(Duration.ofSeconds(5));
		bufferFactory.checkForLeaks();
	}

	@Test // gh-23175
	public void errorInWriteFunction() {

		StepVerifier
				.create(new ChannelSendOperator<>(Mono.just("one"), p -> {
					throw new IllegalStateException("boo");
				}))
				.expectErrorMessage("boo")
				.verify(Duration.ofMillis(5000));

		StepVerifier
				.create(new ChannelSendOperator<>(Mono.empty(), p -> {
					throw new IllegalStateException("boo");
				}))
				.expectErrorMessage("boo")
				.verify(Duration.ofMillis(5000));
	}


	private <T> Mono<Void> sendOperator(Publisher<String> source){
		return new ChannelSendOperator<>(source, writer::send);
	}


	private static class OneByOneAsyncWriter {

		private List<String> items = new ArrayList<>();

		private boolean completed = false;

		private Throwable error;


		public Publisher<Void> send(Publisher<String> publisher) {
			return subscriber -> Executors.newSingleThreadScheduledExecutor().schedule(() ->
							publisher.subscribe(new WriteSubscriber(subscriber)),50, TimeUnit.MILLISECONDS);
		}


		private class WriteSubscriber implements Subscriber<String> {

			private Subscription subscription;

			private final Subscriber<? super Void> subscriber;

			public WriteSubscriber(Subscriber<? super Void> subscriber) {
				this.subscriber = subscriber;
			}

			@Override
			public void onSubscribe(Subscription subscription) {
				this.subscription = subscription;
				this.subscription.request(1);
			}

			@Override
			public void onNext(String item) {
				items.add(item);
				this.subscription.request(1);
			}

			@Override
			public void onError(Throwable ex) {
				error = ex;
				this.subscriber.onError(ex);
			}

			@Override
			public void onComplete() {
				completed = true;
				this.subscriber.onComplete();
			}
		}
	}


	private static class ZeroDemandSubscriber extends BaseSubscriber<DataBuffer> {


		@Override
		protected void hookOnSubscribe(Subscription subscription) {
			// Just subscribe without requesting
		}

		public void signalDemand(long demand) {
			upstream().request(demand);
		}
	}

}
