/*
 * Copyright 2002-2020 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.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;

import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.PooledDataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseCookie;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

Base class for ServerHttpResponse implementations. 
Author:
Rossen Stoyanchev, Juergen Hoeller, Sebastien Deleuze, Brian Clozel
Since:
5.0/**
 * Base class for {@link ServerHttpResponse} implementations.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @author Brian Clozel
 * @since 5.0
 */
public abstract class AbstractServerHttpResponse implements ServerHttpResponse {

	
COMMITTING -> COMMITTED is the period after doCommit is called but before
the response status and headers have been applied to the underlying
response during which time pre-commit actions can still make changes to
the response status and headers.
/**
	 * COMMITTING -> COMMITTED is the period after doCommit is called but before
	 * the response status and headers have been applied to the underlying
	 * response during which time pre-commit actions can still make changes to
	 * the response status and headers.
	 */
	private enum State {NEW, COMMITTING, COMMIT_ACTION_FAILED, COMMITTED}


	private final DataBufferFactory dataBufferFactory;

	@Nullable
	private Integer statusCode;

	private final HttpHeaders headers;

	private final MultiValueMap<String, ResponseCookie> cookies;

	private final AtomicReference<State> state = new AtomicReference<>(State.NEW);

	private final List<Supplier<? extends Mono<Void>>> commitActions = new ArrayList<>(4);

	@Nullable
	private HttpHeaders readOnlyHeaders;


	public AbstractServerHttpResponse(DataBufferFactory dataBufferFactory) {
		this(dataBufferFactory, new HttpHeaders());
	}

	public AbstractServerHttpResponse(DataBufferFactory dataBufferFactory, HttpHeaders headers) {
		Assert.notNull(dataBufferFactory, "DataBufferFactory must not be null");
		Assert.notNull(headers, "HttpHeaders must not be null");
		this.dataBufferFactory = dataBufferFactory;
		this.headers = headers;
		this.cookies = new LinkedMultiValueMap<>();
	}


	@Override
	public final DataBufferFactory bufferFactory() {
		return this.dataBufferFactory;
	}

	@Override
	public boolean setStatusCode(@Nullable HttpStatus status) {
		if (this.state.get() == State.COMMITTED) {
			return false;
		}
		else {
			this.statusCode = (status != null ? status.value() : null);
			return true;
		}
	}

	@Override
	@Nullable
	public HttpStatus getStatusCode() {
		return (this.statusCode != null ? HttpStatus.resolve(this.statusCode) : null);
	}

	@Override
	public boolean setRawStatusCode(@Nullable Integer statusCode) {
		if (this.state.get() == State.COMMITTED) {
			return false;
		}
		else {
			this.statusCode = statusCode;
			return true;
		}
	}

	@Override
	@Nullable
	public Integer getRawStatusCode() {
		return this.statusCode;
	}

	
Set the HTTP status code of the response.
Params:
statusCode – the HTTP status as an integer value
Since:
5.0.1
Deprecated:
as of 5.2.4 in favor of ServerHttpResponse.setRawStatusCode(Integer)./**
	 * Set the HTTP status code of the response.
	 * @param statusCode the HTTP status as an integer value
	 * @since 5.0.1
	 * @deprecated as of 5.2.4 in favor of {@link ServerHttpResponse#setRawStatusCode(Integer)}.
	 */
	@Deprecated
	public void setStatusCodeValue(@Nullable Integer statusCode) {
		if (this.state.get() != State.COMMITTED) {
			this.statusCode = statusCode;
		}
	}

	
Return the HTTP status code of the response.
Returns:
the HTTP status as an integer value
Since:
5.0.1
Deprecated:
as of 5.2.4 in favor of ServerHttpResponse.getRawStatusCode()./**
	 * Return the HTTP status code of the response.
	 * @return the HTTP status as an integer value
	 * @since 5.0.1
	 * @deprecated as of 5.2.4 in favor of {@link ServerHttpResponse#getRawStatusCode()}.
	 */
	@Nullable
	@Deprecated
	public Integer getStatusCodeValue() {
		return this.statusCode;
	}

	@Override
	public HttpHeaders getHeaders() {
		if (this.readOnlyHeaders != null) {
			return this.readOnlyHeaders;
		}
		else if (this.state.get() == State.COMMITTED) {
			this.readOnlyHeaders = HttpHeaders.readOnlyHttpHeaders(this.headers);
			return this.readOnlyHeaders;
		}
		else {
			return this.headers;
		}
	}

	@Override
	public MultiValueMap<String, ResponseCookie> getCookies() {
		return (this.state.get() == State.COMMITTED ?
				CollectionUtils.unmodifiableMultiValueMap(this.cookies) : this.cookies);
	}

	@Override
	public void addCookie(ResponseCookie cookie) {
		Assert.notNull(cookie, "ResponseCookie must not be null");

		if (this.state.get() == State.COMMITTED) {
			throw new IllegalStateException("Can't add the cookie " + cookie +
					"because the HTTP response has already been committed");
		}
		else {
			getCookies().add(cookie.getName(), cookie);
		}
	}

	
Return the underlying server response.
Note: This is exposed mainly for internal framework
use such as WebSocket upgrades in the spring-webflux module.
/**
	 * Return the underlying server response.
	 * <p><strong>Note:</strong> This is exposed mainly for internal framework
	 * use such as WebSocket upgrades in the spring-webflux module.
	 */
	public abstract <T> T getNativeResponse();


	@Override
	public void beforeCommit(Supplier<? extends Mono<Void>> action) {
		this.commitActions.add(action);
	}

	@Override
	public boolean isCommitted() {
		State state = this.state.get();
		return (state != State.NEW && state != State.COMMIT_ACTION_FAILED);
	}

	@Override
	@SuppressWarnings("unchecked")
	public final Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
		// For Mono we can avoid ChannelSendOperator and Reactor Netty is more optimized for Mono.
		// We must resolve value first however, for a chance to handle potential error.
		if (body instanceof Mono) {
			return ((Mono<? extends DataBuffer>) body)
					.flatMap(buffer -> {
						touchDataBuffer(buffer);
						AtomicBoolean subscribed = new AtomicBoolean();
						return doCommit(
								() -> {
									try {
										return writeWithInternal(Mono.fromCallable(() -> buffer)
												.doOnSubscribe(s -> subscribed.set(true))
												.doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release));
									}
									catch (Throwable ex) {
										return Mono.error(ex);
									}
								})
								.doOnError(ex -> DataBufferUtils.release(buffer))
								.doOnCancel(() -> {
									if (!subscribed.get()) {
										DataBufferUtils.release(buffer);
									}
								});
					})
					.doOnError(t -> getHeaders().clearContentHeaders())
					.doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release);
		}
		else {
			return new ChannelSendOperator<>(body, inner -> doCommit(() -> writeWithInternal(inner)))
					.doOnError(t -> getHeaders().clearContentHeaders());
		}
	}

	@Override
	public final Mono<Void> writeAndFlushWith(Publisher<? extends Publisher<? extends DataBuffer>> body) {
		return new ChannelSendOperator<>(body, inner -> doCommit(() -> writeAndFlushWithInternal(inner)))
				.doOnError(t -> getHeaders().clearContentHeaders());
	}

	@Override
	public Mono<Void> setComplete() {
		return !isCommitted() ? doCommit(null) : Mono.empty();
	}

	
A variant of doCommit(Supplier) for a response without no body. 
Returns:
a completion publisher/**
	 * A variant of {@link #doCommit(Supplier)} for a response without no body.
	 * @return a completion publisher
	 */
	protected Mono<Void> doCommit() {
		return doCommit(null);
	}

	
Apply beforeCommit actions, apply the response status and headers/cookies, and write the response body. 
Params:
writeAction – the action to write the response body (may be null)
Returns:
a completion publisher/**
	 * Apply {@link #beforeCommit(Supplier) beforeCommit} actions, apply the
	 * response status and headers/cookies, and write the response body.
	 * @param writeAction the action to write the response body (may be {@code null})
	 * @return a completion publisher
	 */
	protected Mono<Void> doCommit(@Nullable Supplier<? extends Mono<Void>> writeAction) {
		Flux<Void> allActions = Flux.empty();
		if (this.state.compareAndSet(State.NEW, State.COMMITTING)) {
			if (!this.commitActions.isEmpty()) {
				allActions = Flux.concat(Flux.fromIterable(this.commitActions).map(Supplier::get))
						.doOnError(ex -> {
							if (this.state.compareAndSet(State.COMMITTING, State.COMMIT_ACTION_FAILED)) {
								getHeaders().clearContentHeaders();
							}
						});
			}
		}
		else if (this.state.compareAndSet(State.COMMIT_ACTION_FAILED, State.COMMITTING)) {
			// Skip commit actions
		}
		else {
			return Mono.empty();
		}

		allActions = allActions.concatWith(Mono.fromRunnable(() -> {
			applyStatusCode();
			applyHeaders();
			applyCookies();
			this.state.set(State.COMMITTED);
		}));

		if (writeAction != null) {
			allActions = allActions.concatWith(writeAction.get());
		}

		return allActions.then();
	}


	
Write to the underlying the response.
Params:
body – the publisher to write with/**
	 * Write to the underlying the response.
	 * @param body the publisher to write with
	 */
	protected abstract Mono<Void> writeWithInternal(Publisher<? extends DataBuffer> body);

	
Write to the underlying the response, and flush after each Publisher<DataBuffer>. 
Params:
body – the publisher to write and flush with/**
	 * Write to the underlying the response, and flush after each {@code Publisher<DataBuffer>}.
	 * @param body the publisher to write and flush with
	 */
	protected abstract Mono<Void> writeAndFlushWithInternal(Publisher<? extends Publisher<? extends DataBuffer>> body);

	
Write the status code to the underlying response.
This method is called once only.
/**
	 * Write the status code to the underlying response.
	 * This method is called once only.
	 */
	protected abstract void applyStatusCode();

	
Invoked when the response is getting committed allowing sub-classes to
make apply header values to the underlying response.
Note that most sub-classes use an HttpHeaders instance that wraps an adapter to the native response headers such that changes are propagated to the underlying response on the go. That means this callback is typically not used other than for specialized updates such as setting the contentType or characterEncoding fields in a Servlet response. /**
	 * Invoked when the response is getting committed allowing sub-classes to
	 * make apply header values to the underlying response.
	 * <p>Note that most sub-classes use an {@link HttpHeaders} instance that
	 * wraps an adapter to the native response headers such that changes are
	 * propagated to the underlying response on the go. That means this callback
	 * is typically not used other than for specialized updates such as setting
	 * the contentType or characterEncoding fields in a Servlet response.
	 */
	protected abstract void applyHeaders();

	
Add cookies from getHeaders() to the underlying response. This method is called once only. /**
	 * Add cookies from {@link #getHeaders()} to the underlying response.
	 * This method is called once only.
	 */
	protected abstract void applyCookies();

	
Allow sub-classes to associate a hint with the data buffer if it is a
pooled buffer and supports leak tracking.
Params:
buffer – the buffer to attach a hint to
Since:
5.3.2/**
	 * Allow sub-classes to associate a hint with the data buffer if it is a
	 * pooled buffer and supports leak tracking.
	 * @param buffer the buffer to attach a hint to
	 * @since 5.3.2
	 */
	protected void touchDataBuffer(DataBuffer buffer) {
	}

}