/*
 * Copyright 2002-2018 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.server.session;

import java.util.Collections;
import java.util.List;

import org.springframework.http.HttpHeaders;
import org.springframework.util.Assert;
import org.springframework.web.server.ServerWebExchange;

Request and response header-based WebSessionIdResolver. 
Author:
Greg Turnquist, Rob Winch
Since:
5.0/**
 * Request and response header-based {@link WebSessionIdResolver}.
 *
 * @author Greg Turnquist
 * @author Rob Winch
 * @since 5.0
 */
public class HeaderWebSessionIdResolver implements WebSessionIdResolver {

	
Default value for setHeaderName(String). /** Default value for {@link #setHeaderName(String)}. */
	public static final String DEFAULT_HEADER_NAME = "SESSION";


	private String headerName = DEFAULT_HEADER_NAME;


	
Set the name of the session header to use for the session id.
The name is used to extract the session id from the request headers as
well to set the session id on the response headers.
By default set to DEFAULT_HEADER_NAME 
Params:
headerName – the header name/**
	 * Set the name of the session header to use for the session id.
	 * The name is used to extract the session id from the request headers as
	 * well to set the session id on the response headers.
	 * <p>By default set to {@code DEFAULT_HEADER_NAME}
	 * @param headerName the header name
	 */
	public void setHeaderName(String headerName) {
		Assert.hasText(headerName, "'headerName' must not be empty");
		this.headerName = headerName;
	}

	
Return the configured header name.
Returns:
the configured header name/**
	 * Return the configured header name.
	 * @return the configured header name
	 */
	public String getHeaderName() {
		return this.headerName;
	}


	@Override
	public List<String> resolveSessionIds(ServerWebExchange exchange) {
		HttpHeaders headers = exchange.getRequest().getHeaders();
		return headers.getOrDefault(getHeaderName(), Collections.emptyList());
	}

	@Override
	public void setSessionId(ServerWebExchange exchange, String id) {
		Assert.notNull(id, "'id' is required.");
		exchange.getResponse().getHeaders().set(getHeaderName(), id);
	}

	@Override
	public void expireSession(ServerWebExchange exchange) {
		this.setSessionId(exchange, "");
	}

}