/*
 * 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.http.server.reactive;

import java.util.LinkedHashMap;
import java.util.Map;

import reactor.core.publisher.Mono;

import org.springframework.http.HttpStatus;
import org.springframework.util.Assert;

HttpHandler delegating requests to one of several HttpHandler's based on simple, prefix-based mappings. 
This is intended as a coarse-grained mechanism for delegating requests to one of several applications -- each represented by an HttpHandler, with the application "context path" (the prefix-based mapping) exposed via ServerHttpRequest.getPath(). 
Author:
Rossen Stoyanchev
Since:
5.0/**
 * {@code HttpHandler} delegating requests to one of several {@code HttpHandler}'s
 * based on simple, prefix-based mappings.
 *
 * <p>This is intended as a coarse-grained mechanism for delegating requests to
 * one of several applications -- each represented by an {@code HttpHandler}, with
 * the application "context path" (the prefix-based mapping) exposed via
 * {@link ServerHttpRequest#getPath()}.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class ContextPathCompositeHandler implements HttpHandler {

	private final Map<String, HttpHandler> handlerMap;


	public ContextPathCompositeHandler(Map<String, ? extends HttpHandler> handlerMap) {
		Assert.notEmpty(handlerMap, "Handler map must not be empty");
		this.handlerMap = initHandlers(handlerMap);
	}

	private static Map<String, HttpHandler> initHandlers(Map<String, ? extends HttpHandler> map) {
		map.keySet().forEach(ContextPathCompositeHandler::assertValidContextPath);
		return new LinkedHashMap<>(map);
	}

	private static void assertValidContextPath(String contextPath) {
		Assert.hasText(contextPath, "Context path must not be empty");
		if (contextPath.equals("/")) {
			return;
		}
		Assert.isTrue(contextPath.startsWith("/"), "Context path must begin with '/'");
		Assert.isTrue(!contextPath.endsWith("/"), "Context path must not end with '/'");
	}


	@Override
	public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
		// Remove underlying context path first (e.g. Servlet container)
		String path = request.getPath().pathWithinApplication().value();
		return this.handlerMap.entrySet().stream()
				.filter(entry -> path.startsWith(entry.getKey()))
				.findFirst()
				.map(entry -> {
					String contextPath = request.getPath().contextPath().value() + entry.getKey();
					ServerHttpRequest newRequest = request.mutate().contextPath(contextPath).build();
					return entry.getValue().handle(newRequest, response);
				})
				.orElseGet(() -> {
					response.setStatusCode(HttpStatus.NOT_FOUND);
					return response.setComplete();
				});
	}

}