/*
 * Copyright 2014-2019 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
 *
 *     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 de.codecentric.boot.admin.server.web.servlet;

import java.io.IOException;
import java.io.OutputStream;
import java.net.URI;
import java.util.Set;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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.DefaultDataBufferFactory;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.http.server.ServletServerHttpResponse;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.PathMatcher;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.reactive.function.BodyExtractors;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.client.ClientResponse;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.util.UriComponentsBuilder;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import de.codecentric.boot.admin.server.domain.values.InstanceId;
import de.codecentric.boot.admin.server.services.InstanceRegistry;
import de.codecentric.boot.admin.server.web.AdminController;
import de.codecentric.boot.admin.server.web.HttpHeaderFilter;
import de.codecentric.boot.admin.server.web.InstanceWebProxy;
import de.codecentric.boot.admin.server.web.client.InstanceWebClient;

/**
 * Http Handler for proxied requests
 */
@AdminController
public class InstancesProxyController {

	private static final String INSTANCE_MAPPED_PATH = "/instances/{instanceId}/actuator/**";

	private static final String APPLICATION_MAPPED_PATH = "/applications/{applicationName}/actuator/**";

	private final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();

	private final PathMatcher pathMatcher = new AntPathMatcher();

	private final InstanceWebProxy instanceWebProxy;

	private final HttpHeaderFilter httpHeadersFilter;

	private final InstanceRegistry registry;

	private final String adminContextPath;

	public InstancesProxyController(String adminContextPath, Set<String> ignoredHeaders, InstanceRegistry registry,
			InstanceWebClient instanceWebClient) {
		this.adminContextPath = adminContextPath;
		this.registry = registry;
		this.httpHeadersFilter = new HttpHeaderFilter(ignoredHeaders);
		this.instanceWebProxy = new InstanceWebProxy(instanceWebClient);
	}

	@ResponseBody
	@RequestMapping(path = INSTANCE_MAPPED_PATH, method = { RequestMethod.GET, RequestMethod.HEAD, RequestMethod.POST,
			RequestMethod.PUT, RequestMethod.PATCH, RequestMethod.DELETE, RequestMethod.OPTIONS })
	public Mono<Void> endpointProxy(@PathVariable("instanceId") String instanceId, HttpServletRequest servletRequest,
			HttpServletResponse servletResponse) throws IOException {
		ServerHttpRequest request = new ServletServerHttpRequest(servletRequest);
		String endpointLocalPath = this.getEndpointLocalPath(this.adminContextPath + INSTANCE_MAPPED_PATH,
				servletRequest);
		URI uri = UriComponentsBuilder.fromPath(endpointLocalPath).query(request.getURI().getRawQuery()).build(true)
				.toUri();

		// We need to explicitly block until the headers are recieved and write them
		// before the async dispatch.
		// otherwise the FrameworkServlet will add wrong Allow header for OPTIONS request
		Flux<DataBuffer> requestBody = DataBufferUtils.readInputStream(request::getBody, this.bufferFactory, 4096);
		ClientResponse clientResponse = this.instanceWebProxy
				.forward(this.registry.getInstance(InstanceId.of(instanceId)), uri, request.getMethod(),
						this.httpHeadersFilter.filterHeaders(request.getHeaders()),
						BodyInserters.fromDataBuffers(requestBody))
				.block();

		ServerHttpResponse response = new ServletServerHttpResponse(servletResponse);
		response.setStatusCode(clientResponse.statusCode());
		response.getHeaders().addAll(this.httpHeadersFilter.filterHeaders(clientResponse.headers().asHttpHeaders()));
		OutputStream responseBody = response.getBody();
		response.flush();

		return clientResponse.body(BodyExtractors.toDataBuffers()).window(1)
				.concatMap((body) -> writeAndFlush(body, responseBody)).then();
	}

	@ResponseBody
	@RequestMapping(path = APPLICATION_MAPPED_PATH, method = { RequestMethod.GET, RequestMethod.HEAD,
			RequestMethod.POST, RequestMethod.PUT, RequestMethod.PATCH, RequestMethod.DELETE, RequestMethod.OPTIONS })
	public Flux<InstanceWebProxy.InstanceResponse> endpointProxy(
			@PathVariable("applicationName") String applicationName, HttpServletRequest servletRequest) {
		ServerHttpRequest request = new ServletServerHttpRequest(servletRequest);
		String endpointLocalPath = this.getEndpointLocalPath(this.adminContextPath + APPLICATION_MAPPED_PATH,
				servletRequest);
		URI uri = UriComponentsBuilder.fromPath(endpointLocalPath).query(request.getURI().getRawQuery()).build(true)
				.toUri();

		Flux<DataBuffer> cachedBody = DataBufferUtils.readInputStream(request::getBody, this.bufferFactory, 4096)
				.cache();

		return this.instanceWebProxy.forward(this.registry.getInstances(applicationName), uri, request.getMethod(),
				this.httpHeadersFilter.filterHeaders(request.getHeaders()), BodyInserters.fromDataBuffers(cachedBody));
	}

	private String getEndpointLocalPath(String endpointPathPattern, HttpServletRequest servletRequest) {
		String pathWithinApplication = UriComponentsBuilder
				.fromPath(servletRequest.getAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE).toString())
				.toUriString();
		return this.pathMatcher.extractPathWithinPattern(endpointPathPattern, pathWithinApplication);
	}

	private Mono<Void> writeAndFlush(Flux<DataBuffer> body, OutputStream responseBody) {
		return DataBufferUtils.write(body, responseBody).map(DataBufferUtils::release).then(Mono.create((sink) -> {
			try {
				responseBody.flush();
				sink.success();
			}
			catch (IOException ex) {
				sink.error(ex);
			}
		}));
	}

}