/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
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  package org.apache.hc.client5.http.impl.cache;
  
  import java.time.Duration;
  import java.time.Instant;
  import java.util.Iterator;
  
  import org.apache.hc.client5.http.cache.ResponseCacheControl;
  import org.apache.hc.client5.http.utils.DateUtils;
  import org.apache.hc.core5.http.HttpHeaders;
  import org.apache.hc.core5.http.HttpRequest;
  import org.apache.hc.core5.http.HttpResponse;
  import org.apache.hc.core5.http.HttpStatus;
  import org.apache.hc.core5.http.HttpVersion;
  import org.apache.hc.core5.http.Method;
  import org.apache.hc.core5.http.ProtocolVersion;
  import org.apache.hc.core5.http.message.MessageSupport;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  class ResponseCachingPolicy {
  
      /**
       * The default freshness duration for a cached object, in seconds.
       *
       * <p>This constant is used to set the default value for the freshness lifetime of a cached object.
       * When a new object is added to the cache, it will be assigned this duration if no other duration
       * is specified.</p>
       *
       * <p>By default, this value is set to 300 seconds (5 minutes). Applications can customize this
       * value as needed.</p>
       */
       private static final Duration DEFAULT_FRESHNESS_DURATION = Duration.ofMinutes(5);
  
      private static final Logger LOG = LoggerFactory.getLogger(ResponseCachingPolicy.class);
  
      private final boolean sharedCache;
      private final boolean neverCache1_0ResponsesWithQueryString;
      private final boolean neverCache1_1ResponsesWithQueryString;
  
      /**
       * Constructs a new ResponseCachingPolicy with the specified cache policy settings and stale-if-error support.
       *
       * @param sharedCache                           whether to behave as a shared cache (true) or a
       *                                              non-shared/private cache (false)
       * @param neverCache1_0ResponsesWithQueryString {@code true} to never cache HTTP 1.0 responses with a query string,
       *                                              {@code false} to cache if explicit cache headers are found.
       * @param neverCache1_1ResponsesWithQueryString {@code true} to never cache HTTP 1.1 responses with a query string,
       *                                              {@code false} to cache if explicit cache headers are found.
       * @since 5.4
       */
      public ResponseCachingPolicy(
               final boolean sharedCache,
               final boolean neverCache1_0ResponsesWithQueryString,
               final boolean neverCache1_1ResponsesWithQueryString) {
          this.sharedCache = sharedCache;
          this.neverCache1_0ResponsesWithQueryString = neverCache1_0ResponsesWithQueryString;
          this.neverCache1_1ResponsesWithQueryString = neverCache1_1ResponsesWithQueryString;
      }
  
      /**
       * Determine if the {@link HttpResponse} gotten from the origin is a
       * cacheable response.
       *
       * @return {@code true} if response is cacheable
       */
      public boolean isResponseCacheable(final ResponseCacheControl cacheControl, final HttpRequest request, final HttpResponse response) {
          final ProtocolVersion version = request.getVersion() != null ? request.getVersion() : HttpVersion.DEFAULT;
          if (version.compareToVersion(HttpVersion.HTTP_1_1) > 0) {
              if (LOG.isDebugEnabled()) {
                  LOG.debug("Protocol version {} is non-cacheable", version);
              }
              return false;
          }
 
         // Presently only GET and HEAD methods are supported
         final String httpMethod = request.getMethod();
         if (!Method.GET.isSame(httpMethod) && !Method.HEAD.isSame(httpMethod)) {
             if (LOG.isDebugEnabled()) {
                 LOG.debug("{} method response is not cacheable", httpMethod);
             }
             return false;
         }
 
         final int code = response.getCode();
 
         // Should never happen but better be defensive
         if (code <= HttpStatus.SC_INFORMATIONAL) {
             return false;
         }
 
         if (isKnownNonCacheableStatusCode(code)) {
             if (LOG.isDebugEnabled()) {
                 LOG.debug("{} response is not cacheable", code);
             }
             return false;
         }
 
         if (request.getPath().contains("?")) {
             if (neverCache1_0ResponsesWithQueryString && from1_0Origin(response)) {
                 LOG.debug("Response is not cacheable as it had a query string");
                 return false;
             } else if (!neverCache1_1ResponsesWithQueryString && !isExplicitlyCacheable(cacheControl, response)) {
                 LOG.debug("Response is not cacheable as it is missing explicit caching headers");
                 return false;
             }
         }
 
         if (cacheControl.isMustUnderstand() && !understoodStatusCode(code)) {
             // must-understand cache directive overrides no-store
             LOG.debug("Response contains a status code that the cache does not understand, so it's not cacheable");
             return false;
         }
 
         if (isExplicitlyNonCacheable(cacheControl)) {
             LOG.debug("Response is explicitly non-cacheable per cache control directive");
             return false;
         }
 
         if (sharedCache) {
             if (request.containsHeader(HttpHeaders.AUTHORIZATION) &&
                     cacheControl.getSharedMaxAge() == -1 &&
                     !(cacheControl.isPublic() || cacheControl.isMustRevalidate())) {
                 LOG.debug("Request contains private credentials");
                 return false;
             }
         }
 
         // See if the response is tainted
         if (response.countHeaders(HttpHeaders.EXPIRES) > 1) {
             LOG.debug("Multiple Expires headers");
             return false;
         }
 
         if (response.countHeaders(HttpHeaders.DATE) > 1) {
             LOG.debug("Multiple Date headers");
             return false;
         }
 
         final Instant responseDate = DateUtils.parseStandardDate(response, HttpHeaders.DATE);
         final Instant responseExpires = DateUtils.parseStandardDate(response, HttpHeaders.EXPIRES);
 
         if (expiresHeaderLessOrEqualToDateHeaderAndNoCacheControl(cacheControl, responseDate, responseExpires)) {
             LOG.debug("Expires header less or equal to Date header and no cache control directives");
             return false;
         }
 
         // Treat responses with `Vary: *` as essentially non-cacheable.
         final Iterator<String> it = MessageSupport.iterateTokens(response, HttpHeaders.VARY);
         while (it.hasNext()) {
             final String token = it.next();
             if ("*".equals(token)) {
                 if (LOG.isDebugEnabled()) {
                     LOG.debug("Vary: * found");
                 }
                 return false;
             }
         }
 
         return isExplicitlyCacheable(cacheControl, response) || isHeuristicallyCacheable(cacheControl, code, responseDate, responseExpires);
     }
 
     private static boolean isKnownCacheableStatusCode(final int status) {
         return status == HttpStatus.SC_OK ||
                 status == HttpStatus.SC_NON_AUTHORITATIVE_INFORMATION ||
                 status == HttpStatus.SC_MULTIPLE_CHOICES ||
                 status == HttpStatus.SC_MOVED_PERMANENTLY ||
                 status == HttpStatus.SC_GONE;
     }
 
     private static boolean isKnownNonCacheableStatusCode(final int status) {
         return status == HttpStatus.SC_PARTIAL_CONTENT;
     }
 
     private static boolean isUnknownStatusCode(final int status) {
         if (status >= 100 && status <= 101) {
             return false;
         }
         if (status >= 200 && status <= 206) {
             return false;
         }
         if (status >= 300 && status <= 307) {
             return false;
         }
         if (status >= 400 && status <= 417) {
             return false;
         }
         return status < 500 || status > 505;
     }
 
     /**
      * Determines whether the given CacheControl object indicates that the response is explicitly non-cacheable.
      *
      * @param cacheControl the CacheControl object representing the cache-control directive(s) from the HTTP response.
      * @return true if the response is explicitly non-cacheable according to the cache-control directive(s),
      * false otherwise.
      * <p>
      * When cacheControl is non-null:
      * - Returns true if the response contains "no-store" or (if sharedCache is true) "private" cache-control directives.
      * - If the response contains the "no-cache" directive, it is considered cacheable, but requires validation against
      * the origin server before use. In this case, the method returns false.
      * - Returns false for other cache-control directives, implying the response is cacheable.
      * <p>
      * When cacheControl is null, returns false, implying the response is cacheable.
      */
     protected boolean isExplicitlyNonCacheable(final ResponseCacheControl cacheControl) {
         if (cacheControl == null) {
             return false;
         }
         // The response is considered explicitly non-cacheable if it contains
         // "no-store" or (if sharedCache is true) "private" directives.
         // Note that "no-cache" is considered cacheable but requires validation before use.
         return cacheControl.isNoStore() || sharedCache && cacheControl.isCachePrivate();
     }
 
     protected boolean isExplicitlyCacheable(final ResponseCacheControl cacheControl, final HttpResponse response) {
         if (cacheControl.isPublic()) {
             return true;
         }
         if (!sharedCache && cacheControl.isCachePrivate()) {
             return true;
         }
         if (response.containsHeader(HttpHeaders.EXPIRES)) {
             return true;
         }
         if (cacheControl.getMaxAge() > 0) {
             return true;
         }
         if (sharedCache && cacheControl.getSharedMaxAge() > 0) {
             return true;
         }
         return false;
     }
 
     protected boolean isHeuristicallyCacheable(final ResponseCacheControl cacheControl,
                                                final int status,
                                                final Instant responseDate,
                                                final Instant responseExpires) {
         if (isKnownCacheableStatusCode(status)) {
             final Duration freshnessLifetime = calculateFreshnessLifetime(cacheControl, responseDate, responseExpires);
             // calculate freshness lifetime
             if (freshnessLifetime.isNegative()) {
                 if (LOG.isDebugEnabled()) {
                     LOG.debug("Freshness lifetime is invalid");
                 }
                 return false;
             }
             // If the 'immutable' directive is present and the response is still fresh,
             // then the response is considered cacheable without further validation
             if (cacheControl.isImmutable() && responseIsStillFresh(responseDate, freshnessLifetime)) {
                 if (LOG.isDebugEnabled()) {
                     LOG.debug("Response is immutable and fresh, considered cacheable without further validation");
                 }
                 return true;
             }
             if (freshnessLifetime.compareTo(Duration.ZERO) > 0) {
                 return true;
             }
         } else if (isUnknownStatusCode(status)) {
             // a response with an unknown status code MUST NOT be
             // cached
             if (LOG.isDebugEnabled()) {
                 LOG.debug("{} response is unknown", status);
             }
             return false;
         }
         return false;
     }
 
     private boolean expiresHeaderLessOrEqualToDateHeaderAndNoCacheControl(final ResponseCacheControl cacheControl, final Instant responseDate, final Instant expires) {
         if (!cacheControl.isUndefined()) {
             return false;
         }
         if (expires == null || responseDate == null) {
             return false;
         }
         return expires.compareTo(responseDate) <= 0;
     }
 
     private boolean from1_0Origin(final HttpResponse response) {
         final Iterator<String> it = MessageSupport.iterateTokens(response, HttpHeaders.VIA);
         if (it.hasNext()) {
             final String token = it.next();
             return token.startsWith("1.0 ") || token.startsWith("HTTP/1.0 ");
         }
         final ProtocolVersion version = response.getVersion() != null ? response.getVersion() : HttpVersion.DEFAULT;
         return HttpVersion.HTTP_1_0.equals(version);
     }
 
     /**
      * Calculates the freshness lifetime of a response, based on the headers in the response.
      * <p>
      * This method follows the algorithm for calculating the freshness lifetime.
      * The freshness lifetime represents the time interval in seconds during which the response can be served without
      * being considered stale. The freshness lifetime calculation takes into account the s-maxage, max-age, Expires, and
      * Date headers as follows:
      * <ul>
      * <li>If the s-maxage directive is present in the Cache-Control header of the response, its value is used as the
      * freshness lifetime for shared caches, which typically serve multiple users or clients.</li>
      * <li>If the max-age directive is present in the Cache-Control header of the response, its value is used as the
      * freshness lifetime for private caches, which serve a single user or client.</li>
      * <li>If the Expires header is present in the response, its value is used as the expiration time of the response.
      * The freshness lifetime is calculated as the difference between the expiration time and the time specified in the
      * Date header of the response.</li>
      * <li>If none of the above headers are present or if the calculated freshness lifetime is invalid, a default value of
      * 5 minutes is returned.</li>
      * </ul>
      *
      * <p>
      * Note that caching is a complex topic and cache control directives may interact with each other in non-trivial ways.
      * This method provides a basic implementation of the freshness lifetime calculation algorithm and may not be suitable
      * for all use cases. Developers should consult the HTTP caching specifications for more information and consider
      * implementing additional caching mechanisms as needed.
      * </p>
      */
     private Duration calculateFreshnessLifetime(final ResponseCacheControl cacheControl, final Instant responseDate, final Instant responseExpires) {
 
         if (cacheControl.isUndefined()) {
             // If no cache-control header is present, assume no caching directives and return a default value
             return DEFAULT_FRESHNESS_DURATION; // 5 minutes
         }
 
         // Check if s-maxage is present and use its value if it is
         if (cacheControl.getSharedMaxAge() != -1) {
             return Duration.ofSeconds(cacheControl.getSharedMaxAge());
         } else if (cacheControl.getMaxAge() != -1) {
             return Duration.ofSeconds(cacheControl.getMaxAge());
         }
 
         if (responseDate != null && responseExpires != null) {
             return Duration.ofSeconds(responseExpires.getEpochSecond() - responseDate.getEpochSecond());
         }
 
         // If none of the above conditions are met, a heuristic freshness lifetime might be applicable
         return DEFAULT_FRESHNESS_DURATION; // 5 minutes
     }
 
     /**
      * Understood status codes include:
      * - All 2xx (Successful) status codes (200-299)
      * - All 3xx (Redirection) status codes (300-399)
      * - All 4xx (Client Error) status codes up to 417 and 421
      * - All 5xx (Server Error) status codes up to 505
      *
      * @param status The HTTP status code to be checked.
      * @return true if the HTTP status code is understood, false otherwise.
      */
     private boolean understoodStatusCode(final int status) {
         return status >= 200 && status <= 206 ||
                 status >= 300 && status <= 399 ||
                 status >= 400 && status <= 417 ||
                 status == 421 ||
                 status >= 500 && status <= 505;
     }
 
     /**
      * Determines if an HttpResponse is still fresh based on its Date header and calculated freshness lifetime.
      *
      * <p>
      * This method calculates the age of the response from its Date header and compares it with the provided freshness
      * lifetime. If the age is less than the freshness lifetime, the response is considered fresh.
      * </p>
      *
      * <p>
      * Note: If the Date header is missing or invalid, this method assumes the response is not fresh.
      * </p>
      *
      * @param responseDate  The response date.
      * @param freshnessLifetime The calculated freshness lifetime of the HttpResponse.
      * @return {@code true} if the response age is less than its freshness lifetime, {@code false} otherwise.
      */
     private boolean responseIsStillFresh(final Instant responseDate, final Duration freshnessLifetime) {
         if (responseDate == null) {
             // The Date header is missing or invalid. Assuming the response is not fresh.
             return false;
         }
         final Duration age = Duration.between(responseDate, Instant.now());
         return age.compareTo(freshnessLifetime) < 0;
     }
 
 }