/*
    * #%L
    * wcm.io
    * %%
    * Copyright (C) 2022 wcm.io
    * %%
    * 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 io.wcm.handler.url.impl;
  
  import java.util.Enumeration;
  
  import org.apache.commons.lang3.StringUtils;
  import org.apache.sling.api.SlingHttpServletRequest;
  import org.apache.sling.api.adapter.Adaptable;
  import org.jetbrains.annotations.NotNull;
  import org.jetbrains.annotations.Nullable;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Implements auto-detection for Site URL prefix (author or publish).
   * This works only if the adaptable is of SlingHttpServletRequest.
   */
  final class UrlPrefix {
  
    /**
     * String that is provided in site URL config to enable auto-detection.
     */
    public static final String AUTO_DETECTION = "<auto>";
  
    static final String HTTP_HEADER_X_FORWARDED_HOST = "X-Forwarded-Host";
    static final String HTTP_HEADER_X_FORWARDED_PROTO = "X-Forwarded-Proto";
    static final String HTTP_HEADER_HOST = "Host";
    static final String HTTP_HEADER_X_FORWARDED_SSL = "X-Forwarded-SSL";
    static final String VALUE_ON = "on";
  
    private static final Logger log = LoggerFactory.getLogger(UrlPrefix.class);
  
    private UrlPrefix() {
      // static methods only
    }
  
    /**
     * Apply auto-detection to URL prefix.
     * @param configuredUrlPrefix Configured URL prefix
     * @param adaptable Adaptable
     * @return Configured or auto-detected URL prefix
     */
    static @Nullable String applyAutoDetection(@Nullable String configuredUrlPrefix, @NotNull Adaptable adaptable) {
      String urlPrefix = configuredUrlPrefix;
      if (StringUtils.contains(configuredUrlPrefix, AUTO_DETECTION)) {
        // remove auto marker (detection might not be possible if adaptable is not a request)
        urlPrefix = StringUtils.trimToNull(StringUtils.remove(configuredUrlPrefix, AUTO_DETECTION));
        // auto-detect based on request
        if (adaptable instanceof SlingHttpServletRequest) {
          SlingHttpServletRequest request = (SlingHttpServletRequest)adaptable;
          urlPrefix = detectFromForwardedHeader(request);
          if (urlPrefix == null) {
            urlPrefix = detectFromServletRequest(request);
          }
        }
      }
      return urlPrefix;
    }
  
    /**
     * Try to get URL prefix from X-Forwarded header (e.g. in AEMaaCS environment).
     * @param request Request
     * @return Url prefix or null
     */
    private static @Nullable String detectFromForwardedHeader(@NotNull SlingHttpServletRequest request) {
  
      // output request headers to log in TRACE level
      if (log.isTraceEnabled()) {
        StringBuilder output = new StringBuilder();
        Enumeration<String> headers = request.getHeaderNames();
        while (headers.hasMoreElements()) {
          String header = headers.nextElement();
          if (output.length() > 0) {
            output.append("; ");
          }
          output.append(header).append('=').append(request.getHeader(header));
        }
        log.trace("HTTP headers: {}", output);
      }
  
      // this should work for AEMaaCS author
     String forwardedHost = request.getHeader(HTTP_HEADER_X_FORWARDED_HOST);
     String forwardedProto = request.getHeader(HTTP_HEADER_X_FORWARDED_PROTO);
     if (StringUtils.isNotEmpty(forwardedHost) && StringUtils.isNotEmpty(forwardedProto)) {
       return forwardedProto + "://" + forwardedHost;
     }
 
     // this should work for AEMaaCS publish
     String host = request.getHeader(HTTP_HEADER_HOST);
     String forwardedSsl = request.getHeader(HTTP_HEADER_X_FORWARDED_SSL);
     if (StringUtils.isNotEmpty(host) && StringUtils.equalsIgnoreCase(forwardedSsl, VALUE_ON)) {
       return "https://" + host;
     }
 
     return null;
   }
 
   private static @NotNull String detectFromServletRequest(@NotNull SlingHttpServletRequest request) {
     StringBuilder urlPrefix = new StringBuilder();
     urlPrefix.append(request.getScheme()).append("://").append(request.getServerName());
     int port = request.getServerPort();
     if ((request.isSecure() && port != 443) || (!request.isSecure() && port != 80)) {
       urlPrefix.append(':').append(Integer.toString(port));
     }
     return urlPrefix.toString();
   }
 
 }