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package org.apache.juneau.http.header;

import java.time.*;
import java.util.*;
import java.util.function.*;

import org.apache.juneau.http.annotation.*;

/**
 * Represents a parsed <l>Last-Modified</l> HTTP response header.
 *
 * <p>
 * The last modified date for the requested object (in "HTTP-date" format as defined by RFC 7231).
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode w800'>
 *    Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The Last-Modified entity-header field indicates the date and time at which the origin server believes the variant was
 * last modified.
 *
 * <p class='bcode w800'>
 *    Last-Modified  = "Last-Modified" ":" HTTP-date
 * </p>
 *
 * <p>
 * An example of its use is...
 * <p class='bcode w800'>
 *    Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
 * </p>
 *
 * <p>
 * The exact meaning of this header field depends on the implementation of the origin server and the nature of the
 * original resource.
 * For files, it may be just the file system last-modified time.
 * For entities with dynamically included parts, it may be the most recent of the set of last-modify times for its
 * component parts.
 * For database gateways, it may be the last-update time stamp of the record.
 * For virtual objects, it may be the last time the internal state changed.
 *
 * <p>
 * An origin server MUST NOT send a Last-Modified date which is later than the server's time of message origination.
 * In such cases, where the resource's last modification would indicate some time in the future, the server MUST replace
 * that date with the message origination date.
 *
 * <p>
 * An origin server SHOULD obtain the Last-Modified value of the entity as close as possible to the time that it
 * generates the Date value of its response.
 * This allows a recipient to make an accurate assessment of the entity's modification time, especially if the entity
 * changes near the time that the response is generated.
 *
 * <p>
 * HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.
 *
 * <ul class='seealso'>
 *    <li class='extlink'>{@doc ExtRFC2616}
 * </ul>
 */
@Header("Last-Modified")
public class LastModified extends BasicDateHeader {

   private static final long serialVersionUID = 1L;

   /**
    * Convenience creator.
    *
    * @param value
    *    The header value.
    *    <br>Can be any of the following:
    *    <ul>
    *       <li><c>String</c> - An RFC-1123 formated string (e.g. <js>"Sat, 29 Oct 1994 19:43:31 GMT"</js>).
    *       <li>{@link ZonedDateTime}
    *       <li>{@link Calendar}
    *       <li>Anything else - Converted to <c>String</c>.
    *    </ul>
    * @return A new {@link LastModified} object, or <jk>null</jk> if the value was null.
    */
   public static LastModified of(Object value) {
      if (value == null)
         return null;
      return new LastModified(value);
   }

   /**
    * Convenience creator using supplier.
    *
    * <p>
    * Header value is re-evaluated on each call to {@link #getValue()}.
    *
    * @param value
    *    The header value supplier.
    *    <br>Can be any of the following:
    *    <ul>
    *       <li><c>String</c> - An RFC-1123 formated string (e.g. <js>"Sat, 29 Oct 1994 19:43:31 GMT"</js>).
    *       <li>{@link ZonedDateTime}
    *       <li>{@link Calendar}
    *       <li>Anything else - Converted to <c>String</c>.
    *    </ul>
    * @return A new {@link LastModified} object, or <jk>null</jk> if the value was null.
    */
   public static LastModified of(Supplier<?> value) {
      if (value == null)
         return null;
      return new LastModified(value);
   }

   /**
    * Constructor.
    *
    * @param value
    *    The header value.
    *    <br>Can be any of the following:
    *    <ul>
    *       <li><c>String</c> - An RFC-1123 formated string (e.g. <js>"Sat, 29 Oct 1994 19:43:31 GMT"</js>).
    *       <li>{@link ZonedDateTime}
    *       <li>{@link Calendar}
    *       <li>Anything else - Converted to <c>String</c>.
    *       <li>A {@link Supplier} of anything on this list.
    *    </ul>
    */
   public LastModified(Object value) {
      super("Last-Modified", value);
   }

   /**
    * Constructor
    *
    * @param value
    *    The header value.
    */
   public LastModified(String value) {
      this((Object)value);
   }
}