/*
    * ====================================================================
    * 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
   * <http://www.apache.org/>.
   *
   */
  package org.apache.hc.client5.http.cache;
  
  import java.io.Serializable;
  import java.time.Instant;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Date;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.atomic.AtomicReference;
  import java.util.function.Function;
  import java.util.stream.Collectors;
  
  import org.apache.hc.client5.http.utils.DateUtils;
  import org.apache.hc.client5.http.validator.ETag;
  import org.apache.hc.core5.annotation.Contract;
  import org.apache.hc.core5.annotation.Internal;
  import org.apache.hc.core5.annotation.ThreadingBehavior;
  import org.apache.hc.core5.http.Header;
  import org.apache.hc.core5.http.HttpHeaders;
  import org.apache.hc.core5.http.HttpStatus;
  import org.apache.hc.core5.http.MessageHeaders;
  import org.apache.hc.core5.http.Method;
  import org.apache.hc.core5.http.ProtocolException;
  import org.apache.hc.core5.http.message.HeaderGroup;
  import org.apache.hc.core5.util.Args;
  
  /**
   * Structure used to store an {@link org.apache.hc.core5.http.HttpResponse} in a cache.
   * Some entries can optionally depend on system resources that may require
   * explicit deallocation. In such a case {@link #getResource()} should return
   * a non null instance of {@link Resource} that must be deallocated by calling
   * {@link Resource#dispose()} method when no longer used.
   *
   * @since 4.1
   */
  @Contract(threading = ThreadingBehavior.IMMUTABLE)
  public class HttpCacheEntry implements MessageHeaders, Serializable {
  
      private static final long serialVersionUID = -6300496422359477413L;
  
      private final Instant requestDate;
      private final Instant responseDate;
      private final String method;
      private final String requestURI;
      private final HeaderGroup requestHeaders;
      private final int status;
      private final HeaderGroup responseHeaders;
      private final Resource resource;
      private final Set<String> variants;
      private final AtomicReference<Instant> dateRef;
      private final AtomicReference<Instant> expiresRef;
      private final AtomicReference<Instant> lastModifiedRef;
  
      private final AtomicReference<ETag> eTagRef;
  
      /**
       * Internal constructor that makes no validation of the input parameters and makes
       * no copies of the original client request and the origin response.
       */
      @Internal
      public HttpCacheEntry(
              final Instant requestDate,
              final Instant responseDate,
              final String method,
              final String requestURI,
              final HeaderGroup requestHeaders,
              final int status,
              final HeaderGroup responseHeaders,
              final Resource resource,
             final Collection<String> variants) {
         super();
         this.requestDate = requestDate;
         this.responseDate = responseDate;
         this.method = method;
         this.requestURI = requestURI;
         this.requestHeaders = requestHeaders;
         this.status = status;
         this.responseHeaders = responseHeaders;
         this.resource = resource;
         this.variants = variants != null ? Collections.unmodifiableSet(new HashSet<>(variants)) : null;
         this.dateRef = new AtomicReference<>();
         this.expiresRef = new AtomicReference<>();
         this.lastModifiedRef = new AtomicReference<>();
         this.eTagRef = new AtomicReference<>();
     }
 
     /**
      * Create a new {@link HttpCacheEntry} with variants.
      * @param requestDate
      *          Date/time when the request was made (Used for age
      *            calculations)
      * @param responseDate
      *          Date/time that the response came back (Used for age
      *            calculations)
      * @param status
      *          HTTP status from origin response
      * @param responseHeaders
      *          Header[] from original HTTP Response
      * @param resource representing origin response body
      * @param variantMap describing cache entries that are variants
      *   of this parent entry; this maps a "variant key" (derived
      *   from the varying request headers) to a "cache key" (where
      *   in the cache storage the particular variant is located)
      * @deprecated  Use {{@link HttpCacheEntryFactory}
      */
     @Deprecated
     public HttpCacheEntry(
             final Date requestDate,
             final Date responseDate,
             final int status,
             final Header[] responseHeaders,
             final Resource resource,
             final Map<String, String> variantMap) {
         this(DateUtils.toInstant(requestDate), DateUtils.toInstant(responseDate), status, responseHeaders, resource, variantMap);
     }
 
     /**
      * Create a new {@link HttpCacheEntry} with variants.
      *
      * @param requestDate     Date/time when the request was made (Used for age calculations)
      * @param responseDate    Date/time that the response came back (Used for age calculations)
      * @param status          HTTP status from origin response
      * @param responseHeaders Header[] from original HTTP Response
      * @param resource        representing origin response body
      * @param variantMap      describing cache entries that are variants of this parent entry; this
      *                        maps a "variant key" (derived from the varying request headers) to a
      *                        "cache key" (where in the cache storage the particular variant is
      *                        located)
      * @deprecated  Use {{@link HttpCacheEntryFactory}
      */
     @Deprecated
     public HttpCacheEntry(
             final Instant requestDate,
             final Instant responseDate,
             final int status,
             final Header[] responseHeaders,
             final Resource resource,
             final Map<String, String> variantMap) {
         super();
         Args.notNull(requestDate, "Request date");
         Args.notNull(responseDate, "Response date");
         Args.check(status >= HttpStatus.SC_SUCCESS, "Status code");
         Args.notNull(responseHeaders, "Response headers");
         this.requestDate = requestDate;
         this.responseDate = responseDate;
         this.method = Method.GET.name();
         this.requestURI = "/";
         this.requestHeaders = new HeaderGroup();
         this.status = status;
         this.responseHeaders = new HeaderGroup();
         this.responseHeaders.setHeaders(responseHeaders);
         this.resource = resource;
         this.variants = variantMap != null ? Collections.unmodifiableSet(new HashSet<>(variantMap.keySet())) : null;
         this.dateRef = new AtomicReference<>();
         this.expiresRef = new AtomicReference<>();
         this.lastModifiedRef = new AtomicReference<>();
         this.eTagRef = new AtomicReference<>();
     }
 
     /**
      * Create a new {@link HttpCacheEntry}.
      *
      * @param requestDate     Date/time when the request was made (Used for age calculations)
      * @param responseDate    Date/time that the response came back (Used for age calculations)
      * @param status          HTTP status from origin response
      * @param responseHeaders Header[] from original HTTP Response
      * @param resource        representing origin response body
      * @deprecated  Use {{@link HttpCacheEntryFactory}
      */
     @Deprecated
     public HttpCacheEntry(final Date requestDate, final Date responseDate, final int status,
                           final Header[] responseHeaders, final Resource resource) {
         this(requestDate, responseDate, status, responseHeaders, resource, new HashMap<>());
     }
 
     /**
      * Create a new {@link HttpCacheEntry}.
      *
      * @param requestDate
      *          Date/time when the request was made (Used for age
      *            calculations)
      * @param responseDate
      *          Date/time that the response came back (Used for age
      *            calculations)
      * @param status
      *          HTTP status from origin response
      * @param responseHeaders
      *          Header[] from original HTTP Response
      * @param resource representing origin response body
      *
      * @deprecated  Use {{@link HttpCacheEntryFactory}
      */
     @Deprecated
     public HttpCacheEntry(final Instant requestDate, final Instant responseDate, final int status,
                           final Header[] responseHeaders, final Resource resource) {
         this(requestDate, responseDate, status, responseHeaders, resource, new HashMap<>());
     }
 
     /**
      * Returns the status from the origin {@link org.apache.hc.core5.http.HttpResponse}.
      */
     public int getStatus() {
         return status;
     }
 
     /**
      * Returns the time the associated origin request was initiated by the
      * caching module.
      * @return {@link Date}
      * @deprecated USe {@link #getRequestInstant()}
      */
     @Deprecated
     public Date getRequestDate() {
         return DateUtils.toDate(requestDate);
     }
 
     /**
      * Returns the time the associated origin request was initiated by the
      * caching module.
      * @return {@link Instant}
      * @since 5.2
      */
     public Instant getRequestInstant() {
         return requestDate;
     }
 
     /**
      * Returns the time the origin response was received by the caching module.
      * @return {@link Date}
      * @deprecated  Use {@link #getResponseInstant()}
      */
     @Deprecated
     public Date getResponseDate() {
         return DateUtils.toDate(responseDate);
     }
 
     /**
      * Returns the time the origin response was received by the caching module.
      *
      * @return {@link Instant}
      * @since 5.2
      */
     public Instant getResponseInstant() {
         return responseDate;
     }
 
     /**
      * Returns all the headers that were on the origin response.
      */
     @Override
     public Header[] getHeaders() {
         return responseHeaders.getHeaders();
     }
 
     /**
      * Returns the first header from the origin response with the given
      * name.
      */
     @Override
     public Header getFirstHeader(final String name) {
         return responseHeaders.getFirstHeader(name);
     }
 
     /**
      * @since 5.0
      */
     @Override
     public Header getLastHeader(final String name) {
         return responseHeaders.getLastHeader(name);
     }
 
     /**
      * Gets all the headers with the given name that were on the origin
      * response.
      */
     @Override
     public Header[] getHeaders(final String name) {
         return responseHeaders.getHeaders(name);
     }
 
     /**
      * @since 5.0
      */
     @Override
     public boolean containsHeader(final String name) {
         return responseHeaders.containsHeader(name);
     }
 
     /**
      * @since 5.0
      */
     @Override
     public int countHeaders(final String name) {
         return responseHeaders.countHeaders(name);
     }
 
     /**
      * @since 5.0
      */
     @Override
     public Header getHeader(final String name) throws ProtocolException {
         return responseHeaders.getHeader(name);
     }
 
     /**
      * @since 5.0
      */
     @Override
     public Iterator<Header> headerIterator() {
         return responseHeaders.headerIterator();
     }
 
     /**
      * @since 5.0
      */
     @Override
     public Iterator<Header> headerIterator(final String name) {
         return responseHeaders.headerIterator(name);
     }
 
     /**
      * @since 5.4
      */
     public MessageHeaders responseHeaders() {
         return responseHeaders;
     }
 
     /**
      * Gets the Date value of the "Date" header or null if the header is missing or cannot be
      * parsed.
      *
      * @since 4.3
      */
     public Date getDate() {
         return DateUtils.toDate(getInstant());
     }
 
     private static final Instant NON_VALUE = Instant.ofEpochSecond(Instant.MIN.getEpochSecond(), 0);
 
     private Instant getInstant(final AtomicReference<Instant> ref, final String headerName) {
         Instant instant = ref.get();
         if (instant == null) {
             instant = DateUtils.parseStandardDate(this, headerName);
             if (instant == null) {
                 instant = NON_VALUE;
             }
             if (!ref.compareAndSet(null, instant)) {
                 instant = ref.get();
             }
         }
         return instant != null && instant != NON_VALUE ? instant : null;
     }
 
     /**
      * @since 5.2
      */
     public Instant getInstant() {
         return getInstant(dateRef, HttpHeaders.DATE);
     }
 
     /**
      * @since 5.4
      */
     public Instant getExpires() {
         return getInstant(expiresRef, HttpHeaders.EXPIRES);
     }
 
     /**
      * @since 5.4
      */
     public Instant getLastModified() {
         return getInstant(lastModifiedRef, HttpHeaders.LAST_MODIFIED);
     }
 
     /**
      * @since 5.4
      */
     public ETag getETag() {
         ETag eTag = eTagRef.get();
         if (eTag == null) {
             eTag = ETag.get(this);
             if (eTag == null) {
                 return null;
             }
             if (!eTagRef.compareAndSet(null, eTag)) {
                 eTag = eTagRef.get();
             }
         }
         return eTag;
     }
 
     /**
      * Returns the {@link Resource} containing the origin response body.
      */
     public Resource getResource() {
         return this.resource;
     }
 
     /**
      * Indicates whether the origin response indicated the associated
      * resource had variants (i.e. that the Vary header was set on the
      * origin response).
      */
     public boolean hasVariants() {
         return variants != null;
     }
 
     /**
      * Returns all known variants.
      *
      * @since 5.4
      */
     public Set<String> getVariants() {
         return variants != null ? variants : Collections.emptySet();
     }
 
     /**
      * @deprecated No longer applicable. Use {@link #getVariants()} instead.
      */
     @Deprecated
     public Map<String, String> getVariantMap() {
         return variants != null ? variants.stream()
                 .collect(Collectors.toMap(Function.identity(), e -> e + requestURI)) : Collections.emptyMap();
     }
 
     /**
      * Returns the HTTP request method that was used to create the cached
      * response entry.
      *
      * @since 4.4
      */
     public String getRequestMethod() {
         return method;
     }
 
     /**
      * @since 5.4
      */
     public String getRequestURI() {
         return requestURI;
     }
 
     /**
      * @since 5.4
      */
     public MessageHeaders requestHeaders() {
         return requestHeaders;
     }
 
     /**
      * @since 5.4
      */
     public Iterator<Header> requestHeaderIterator() {
         return requestHeaders.headerIterator();
     }
 
     /**
      * @since 5.4
      */
     public Iterator<Header> requestHeaderIterator(final String headerName) {
         return requestHeaders.headerIterator(headerName);
     }
 
     /**
      * Tests if the given {@link HttpCacheEntry} is newer than the given {@link MessageHeaders}
      * by comparing values of their {@literal DATE} header. In case the given entry, or the message,
      * or their {@literal DATE} headers are null, this method returns {@code false}.
      *
      * @since 5.4
      */
     public static boolean isNewer(final HttpCacheEntry entry, final MessageHeaders message) {
         if (entry == null || message == null) {
             return false;
         }
         final Instant cacheDate = entry.getInstant();
         if (cacheDate == null) {
             return false;
         }
         final Instant messageDate = DateUtils.parseStandardDate(message, HttpHeaders.DATE);
         if (messageDate == null) {
             return false;
         }
         return cacheDate.compareTo(messageDate) > 0;
     }
 
     /**
      * Provides a string representation of this instance suitable for
      * human consumption.
      */
     @Override
     public String toString() {
         return "HttpCacheEntry{" +
                 "requestDate=" + requestDate +
                 ", responseDate=" + responseDate +
                 ", method='" + method + '\'' +
                 ", requestURI='" + requestURI + '\'' +
                 ", requestHeaders=" + requestHeaders +
                 ", status=" + status +
                 ", responseHeaders=" + responseHeaders +
                 ", resource=" + resource +
                 ", variants=" + variants +
                 '}';
     }
 }