/*
 * Copyright 2002-2017 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
 *
 *      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 org.springframework.web.reactive.socket.server.upgrade;

import java.io.IOException;
import java.security.Principal;
import java.util.Collections;
import java.util.Optional;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.websocket.Endpoint;

import org.apache.tomcat.websocket.server.WsServerContainer;
import reactor.core.publisher.Mono;

import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.http.server.reactive.ServletServerHttpRequest;
import org.springframework.http.server.reactive.ServletServerHttpResponse;
import org.springframework.util.Assert;
import org.springframework.web.reactive.socket.HandshakeInfo;
import org.springframework.web.reactive.socket.WebSocketHandler;
import org.springframework.web.reactive.socket.adapter.StandardWebSocketHandlerAdapter;
import org.springframework.web.reactive.socket.adapter.StandardWebSocketSession;
import org.springframework.web.reactive.socket.server.RequestUpgradeStrategy;
import org.springframework.web.server.ServerWebExchange;

/**
 * A {@link RequestUpgradeStrategy} for use with Tomcat.
 *
 * @author Violeta Georgieva
 * @since 5.0
 */
@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
public class TomcatRequestUpgradeStrategy implements RequestUpgradeStrategy {

	private static final String SERVER_CONTAINER_ATTR = "javax.websocket.server.ServerContainer";


	@Override
	public Mono<Void> upgrade(ServerWebExchange exchange, WebSocketHandler handler, Optional<String> subProtocol){
		ServerHttpRequest request = exchange.getRequest();
		ServerHttpResponse response = exchange.getResponse();

		HttpServletRequest servletRequest = getHttpServletRequest(request);
		HttpServletResponse servletResponse = getHttpServletResponse(response);

		Endpoint endpoint = new StandardWebSocketHandlerAdapter(handler,
				session -> {
					HandshakeInfo info = getHandshakeInfo(exchange, subProtocol);
					DataBufferFactory factory = response.bufferFactory();
					return new StandardWebSocketSession(session, info, factory);
				});

		String requestURI = servletRequest.getRequestURI();
		DefaultServerEndpointConfig config = new DefaultServerEndpointConfig(requestURI, endpoint);
		config.setSubprotocols(subProtocol.map(Collections::singletonList).orElse(Collections.emptyList()));

		try {
			WsServerContainer container = getContainer(servletRequest);
			container.doUpgrade(servletRequest, servletResponse, config, Collections.emptyMap());
		}
		catch (ServletException | IOException ex) {
			return Mono.error(ex);
		}

		return Mono.empty();
	}

	private HttpServletRequest getHttpServletRequest(ServerHttpRequest request) {
		Assert.isInstanceOf(ServletServerHttpRequest.class, request, "ServletServerHttpRequest required");
		return ((ServletServerHttpRequest) request).getServletRequest();
	}

	private HttpServletResponse getHttpServletResponse(ServerHttpResponse response) {
		Assert.isInstanceOf(ServletServerHttpResponse.class, response, "ServletServerHttpResponse required");
		return ((ServletServerHttpResponse) response).getServletResponse();
	}

	private HandshakeInfo getHandshakeInfo(ServerWebExchange exchange, Optional<String> protocol) {
		ServerHttpRequest request = exchange.getRequest();
		Mono<Principal> principal = exchange.getPrincipal();
		return new HandshakeInfo(request.getURI(), request.getHeaders(), principal, protocol);
	}

	private WsServerContainer getContainer(HttpServletRequest request) {
		Object container = request.getServletContext().getAttribute(SERVER_CONTAINER_ATTR);
		Assert.state(container instanceof WsServerContainer,
				"No 'javax.websocket.server.ServerContainer' ServletContext attribute in a Tomcat container");
		return (WsServerContainer) container;
	}

}