/*
 * 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.web.reactive.socket.server.upgrade;

import java.util.function.Supplier;

import reactor.core.publisher.Mono;
import reactor.netty.http.server.HttpServerResponse;

import org.springframework.core.io.buffer.NettyDataBufferFactory;
import org.springframework.http.server.reactive.AbstractServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpResponseDecorator;
import org.springframework.lang.Nullable;
import org.springframework.web.reactive.socket.HandshakeInfo;
import org.springframework.web.reactive.socket.WebSocketHandler;
import org.springframework.web.reactive.socket.adapter.NettyWebSocketSessionSupport;
import org.springframework.web.reactive.socket.adapter.ReactorNettyWebSocketSession;
import org.springframework.web.reactive.socket.server.RequestUpgradeStrategy;
import org.springframework.web.server.ServerWebExchange;

/**
 * A {@link RequestUpgradeStrategy} for use with Reactor Netty.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class ReactorNettyRequestUpgradeStrategy implements RequestUpgradeStrategy {

	private int maxFramePayloadLength = NettyWebSocketSessionSupport.DEFAULT_FRAME_MAX_SIZE;


	/**
	 * Configure the maximum allowable frame payload length. Setting this value
	 * to your application's requirement may reduce denial of service attacks
	 * using long data frames.
	 * <p>Corresponds to the argument with the same name in the constructor of
	 * {@link io.netty.handler.codec.http.websocketx.WebSocketServerHandshakerFactory
	 * WebSocketServerHandshakerFactory} in Netty.
	 * <p>By default set to 65536 (64K).
	 * @param maxFramePayloadLength the max length for frames.
	 * @since 5.1
	 */
	public void setMaxFramePayloadLength(Integer maxFramePayloadLength) {
		this.maxFramePayloadLength = maxFramePayloadLength;
	}

	/**
	 * Return the configured max length for frames.
	 * @since 5.1
	 */
	public int getMaxFramePayloadLength() {
		return this.maxFramePayloadLength;
	}


	@Override
	public Mono<Void> upgrade(ServerWebExchange exchange, WebSocketHandler handler,
			@Nullable String subProtocol, Supplier<HandshakeInfo> handshakeInfoFactory) {

		ServerHttpResponse response = exchange.getResponse();
		HttpServerResponse reactorResponse = getNativeResponse(response);
		HandshakeInfo handshakeInfo = handshakeInfoFactory.get();
		NettyDataBufferFactory bufferFactory = (NettyDataBufferFactory) response.bufferFactory();

		return reactorResponse.sendWebsocket(subProtocol, this.maxFramePayloadLength,
				(in, out) -> {
					ReactorNettyWebSocketSession session =
							new ReactorNettyWebSocketSession(
									in, out, handshakeInfo, bufferFactory, this.maxFramePayloadLength);
					return handler.handle(session);
				});
	}

	private static HttpServerResponse getNativeResponse(ServerHttpResponse response) {
		if (response instanceof AbstractServerHttpResponse) {
			return ((AbstractServerHttpResponse) response).getNativeResponse();
		}
		else if (response instanceof ServerHttpResponseDecorator) {
			return getNativeResponse(((ServerHttpResponseDecorator) response).getDelegate());
		}
		else {
			throw new IllegalArgumentException(
					"Couldn't find native response in " + response.getClass().getName());
		}
	}

}
