/*-
    * #%L
    * Spring Stomp Server
    * ===============================================================
    * Copyright (C) 2020 - 2023 Brabenetz Harald, Austria
    * ===============================================================
    * 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.
   * #L%
   */
  package net.brabenetz.app.springstompserver.config;
  
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.context.ApplicationListener;
  import org.springframework.http.HttpEntity;
  import org.springframework.http.HttpHeaders;
  import org.springframework.http.HttpMethod;
  import org.springframework.http.ResponseEntity;
  import org.springframework.messaging.Message;
  import org.springframework.messaging.simp.SimpMessagingTemplate;
  import org.springframework.messaging.simp.stomp.StompHeaderAccessor;
  import org.springframework.messaging.support.MessageBuilder;
  import org.springframework.messaging.support.NativeMessageHeaderAccessor;
  import org.springframework.stereotype.Component;
  import org.springframework.util.ObjectUtils;
  import org.springframework.web.client.RestTemplate;
  import org.springframework.web.socket.messaging.SessionSubscribeEvent;
  
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  import java.util.regex.Matcher;
  
  /**
   * Listen on all subscriptions, and if a subscription starts with {@link WebSocketInitLoadConfigProperties#getDestinationPatterns()}, then directly send an
   * initial load from {@link WebSocketInitLoadConfigProperties#getProxyUrl()} to the subscribed topic.
   */
  @Component
  public class StompSubscriptionEventListener implements ApplicationListener<SessionSubscribeEvent> {
  
      @Autowired
      private SimpMessagingTemplate messagingTemplate;
  
      @Autowired
      private WebSocketInitLoadConfigProperties initLoadConfigProperties;
  
      private final RestTemplate restTemplate = new RestTemplate();
  
      @Override
      public void onApplicationEvent(final SessionSubscribeEvent event) {
          if (ObjectUtils.isEmpty(initLoadConfigProperties.getProxyUrl())) {
              // nothing to proxy
              return;
          }
  
          StompHeaderAccessor sha = StompHeaderAccessor.wrap(event.getMessage());
          String destination = sha.getDestination();
          @SuppressWarnings("unchecked")
          Map<String, List<String>> nativHeaders = (Map<String, List<String>>) sha.getHeader(NativeMessageHeaderAccessor.NATIVE_HEADERS);
  
          Matcher userDestMatcher = initLoadConfigProperties.getDestinationPatterns().matcher(destination);
          if (userDestMatcher.matches()) {
              // call proxy-server
              String proxyUrl = getProxyUrl(userDestMatcher, initLoadConfigProperties.getProxyUrl());
              HttpHeaders headers = new HttpHeaders();
              nativHeaders.forEach((k, v) -> headers.addAll(k, v));
              ResponseEntity<byte[]> response = restTemplate.exchange(proxyUrl, HttpMethod.GET, new HttpEntity<>(headers), byte[].class);
  
              // relay response to the subscribed subject:
              HttpHeaders respHeaders = response.getHeaders();
              Message<byte[]> stompMessage = MessageBuilder
                      .withPayload(response.getBody())
                      .copyHeaders(Collections.singletonMap(NativeMessageHeaderAccessor.NATIVE_HEADERS, respHeaders))
                      .build();
              messagingTemplate.send(destination, stompMessage);
          }
      }
  
      private String getProxyUrl(final Matcher userDestMatcher, final String proxyUrlTemplate) {
          userDestMatcher.groupCount();
          String proxyUrl = proxyUrlTemplate;
          for (int i = 1; i <= userDestMatcher.groupCount(); i++) {
              proxyUrl = proxyUrl.replaceAll("\\$\\{group-" + i + "\\}", userDestMatcher.group(i));
          }
          return proxyUrl;
      }
  
  }