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package org.apache.juneau.http.header;

import static org.apache.juneau.internal.StringUtils.*;

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

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

/**
 * Represents a parsed <l>Retry-After</l> HTTP response header.
 *
 * <p>
 * If an entity is temporarily unavailable, this instructs the client to try again later.
 * Value could be a specified period of time (in seconds) or a HTTP-date.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode w800'>
 *    Retry-After: 120
 *    Retry-After: Fri, 07 Nov 2014 23:59:59 GMT
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The Retry-After response-header field can be used with a 503 (Service Unavailable) response to indicate how long the
 * service is expected to be unavailable to the requesting client.
 * This field MAY also be used with any 3xx (Redirection) response to indicate the minimum time the user-agent is asked
 * wait before issuing the redirected request.
 * The value of this field can be either an HTTP-date or an integer number of seconds (in decimal) after the time of the
 * response.
 *
 * <p class='bcode w800'>
 *    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
 * </p>
 *
 * <p>
 * Two examples of its use are
 * <p class='bcode w800'>
 *    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
 *    Retry-After: 120
 * </p>
 *
 * <p>
 * In the latter example, the delay is 2 minutes.
 *
 * <ul class='seealso'>
 *    <li class='extlink'>{@doc ExtRFC2616}
 * </ul>
 */
@Header("Retry-After")
public class RetryAfter extends BasicDateHeader {

   private static final long serialVersionUID = 1L;

   private final Object value;  // Only set if value is an integer.

   /**
    * Convenience creator.
    *
    * @param value
    *    The header value.
    *    <br>Can be any of the following:
    *    <ul>
    *       <li>{@link String}
    *       <li>Anything else - Converted to <c>String</c> then parsed.
    *    </ul>
    * @return A new {@link RetryAfter} object.
    */
   public static RetryAfter of(Object value) {
      if (value == null)
         return null;
      return new RetryAfter(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>{@link String}
    *       <li>Anything else - Converted to <c>String</c> then parsed.
    *    </ul>
    * @return A new {@link RetryAfter} object.
    */
   public static RetryAfter of(Supplier<?> value) {
      if (value == null)
         return null;
      return new RetryAfter(value);
   }

   /**
    * Constructor.
    *
    * @param value
    *    The header value.
    *    <br>Can be any of the following:
    *    <ul>
    *       <li>{@link String}
    *       <li>{@link ZonedDateTime}
    *       <li>{@link Calendar}
    *       <li>{@link Number}
    *       <li>Anything else - Converted to <c>String</c> then parsed.
    *       <li>A {@link Supplier} of anything on this list.
    *    </ul>
    */
   public RetryAfter(Object value) {
      super("Retry-After", dateValue(value));
      this.value = intValue(value);
   }

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

   private static Object dateValue(Object o) {
      Object o2 = unwrap(o);
      if (o2 == null || isInt(o2))
         return null;
      return o;
   }

   private static Object intValue(Object o) {
      Object o2 = unwrap(o);
      if (o2 == null || isInt(o2))
         return o;
      return null;
   }

   private static boolean isInt(Object o) {
      if (o instanceof Number)
         return true;
      String s = o.toString();
      char c0 = charAt(s, 0);
      return Character.isDigit(c0);
   }

   @Override /* Header */
   public String getValue() {
      if (value == null)
         return super.getValue();
      Object o = unwrap(value);
      return (o == null ? null : o.toString());
   }

   /**
    * Returns this header value as an integer.
    *
    * @return This header value as a integer, or <c>-1</c> if the value is not an integer.
    */
   public int asInt() {
      if (value != null) {
         Object o = unwrap(value);
         return o == null ? -1 : Integer.parseInt(o.toString());
      }
      return -1;
   }
}