/*
 * 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.
 */
package org.apache.juneau.http.classic.header;

import static java.time.format.DateTimeFormatter.*;
import static org.apache.juneau.commons.utils.Shorts.*;

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

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

/**
 * Represents a parsed <l>If-Range</l> HTTP request header.
 *
 * <p>
 * If the entity is unchanged, send me the part(s) that I am missing; otherwise, send me the entire new entity.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 *    If-Range: "737060cd8c284d8af7ad3082f209582d"
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * If a client has a partial copy of an entity in its cache, and wishes to have an up-to-date copy of the entire entity
 * in its cache, it could use the Range request-header with a conditional GET (using either or both of
 * If-Unmodified-Since and If-Match.)
 * However, if the condition fails because the entity has been modified, the client would then have to make a second
 * request to obtain the entire current entity-body.
 *
 * <p>
 * The If-Range header allows a client to "short-circuit" the second request.
 * Informally, its meaning is `if the entity is unchanged, send me the part(s) that I am missing; otherwise, send me
 * the entire new entity'.
 * <p class='bcode'>
 *    If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
 * </p>
 *
 * <p>
 * If the client has no entity tag for an entity, but does have a Last- Modified date, it MAY use that date in an
 * If-Range header.
 * (The server can distinguish between a valid HTTP-date and any form of entity-tag by examining no more than two
 * characters.)
 * The If-Range header SHOULD only be used together with a Range header, and MUST be ignored if the request does not
 * include a Range header, or if the server does not support the sub-range operation.
 *
 * <p>
 * If the entity tag given in the If-Range header matches the current entity tag for the entity, then the server SHOULD
 * provide the specified sub-range of the entity using a 206 (Partial content) response.
 * If the entity tag does not match, then the server SHOULD return the entire entity using a 200 (OK) response.
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/JuneauRestCommon">juneau-rest-common</a>
 *    <li class='extlink'><a class="doclink" href="https://www.w3.org/Protocols/rfc2616/rfc2616.html">Hypertext Transfer Protocol -- HTTP/1.1</a>
 * </ul>
 *
 * @serial exclude
 */
@Header("If-Range")
@SuppressWarnings({
   "java:S2160" // equals() inherited from BasicHeader compares name+value; no additional equality-relevant fields
})
public class IfRange extends BasicDateHeader {
   private static final long serialVersionUID = 1L;
   private static final String NAME = "If-Range";

   /**
    * Static creator.
    *
    * @param value
    *    The header value.
    *    <br>Can be <jk>null</jk>.
    * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
    */
   public static IfRange of(EntityTag value) {
      return value == null ? null : new IfRange(value);
   }

   /**
    * Static creator.
    *
    * @param value
    *    The header value.
    *    <br>Must be an RFC-1123 formated string (e.g. <js>"Sat, 29 Oct 1994 19:43:31 GMT"</js>).
    *    <br>Can be <jk>null</jk>.
    * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
    */
   public static IfRange of(String value) {
      return value == null ? null : new IfRange(value);
   }

   /**
    * Static creator with delayed value.
    *
    * <p>
    * Header value is re-evaluated on each call to {@link #getValue()}.
    *
    * @param value
    *    The supplier of the header value.
    *    <br>Supplier must supply either {@link EntityTag} or {@link ZonedDateTime} objects.
    *    <br>Can be <jk>null</jk>.
    * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
    */
   public static IfRange of(Supplier<?> value) {
      return value == null ? null : new IfRange(value);
   }

   /**
    * Static creator.
    *
    * @param value
    *    The header value.
    *    <br>Can be <jk>null</jk>.
    * @return A new header bean, or <jk>null</jk> if the name is <jk>null</jk> or empty or the value is <jk>null</jk>.
    */
   public static IfRange of(ZonedDateTime value) {
      return value == null ? null : new IfRange(value);
   }

   private static boolean isEtag(String s) {
      return s.startsWith("\"") || s.startsWith("W/");
   }

   private final transient EntityTag value;

   private final transient Supplier<?> supplier;

   /**
    * Constructor.
    *
    * @param value
    *    The header value.
    *    <br>Can be <jk>null</jk> to create a header with no value.
    */
   public IfRange(EntityTag value) {
      super(NAME, (String)null);
      this.value = value;
      this.supplier = null;
   }

   /**
    * Constructor.
    *
    * @param value
    *    The header value.
    *    <br>Must be an RFC-1123 formated string (e.g. <js>"Sat, 29 Oct 1994 19:43:31 GMT"</js>).
    *    <br>Must not be <jk>null</jk> (a <jk>null</jk> argument throws {@link NullPointerException}).
    */
   public IfRange(String value) {
      super(NAME, isEtag(value) ? null : value);
      this.value = isEtag(value) ? EntityTag.of(value) : null;
      this.supplier = null;
   }

   /**
    * Constructor with delayed value.
    *
    * <p>
    * Header value is re-evaluated on each call to {@link #getValue()}.
    *
    * @param value
    *    The supplier of the header value.
    *    <br>Supplier must supply either {@link EntityTag} or {@link ZonedDateTime} objects.
    *    <br>Can be <jk>null</jk> to create a header with no value.
    */
   public IfRange(Supplier<?> value) {
      super(NAME, (String)null);
      this.value = null;
      supplier = value;
   }

   /**
    * Constructor.
    *
    * @param value
    *    The header value.
    *    <br>Can be <jk>null</jk> to create a header with no value.
    */
   public IfRange(ZonedDateTime value) {
      super(NAME, value);
      this.value = null;
      this.supplier = null;
   }

   /**
    * Returns this header as an {@link EntityTag}.
    *
    * @return This header as an {@link EntityTag}.
    */
   public Optional<EntityTag> asEntityTag() {
      if (nn(supplier)) {
         Object o = supplier.get();
         return o(o instanceof EntityTag o2 ? o2 : null);
      }
      return o(value);
   }

   @Override /* Overridden from Header */
   public String getValue() {
      if (nn(supplier)) {
         Object o = supplier.get();
         if (o == null)
            return null;
         if (o instanceof EntityTag o2) {
            return o2.toString();
         } else if (o instanceof ZonedDateTime o2) {
            return RFC_1123_DATE_TIME.format(o2);
         }
         throw rex("Invalid object type returned by supplier: %s", cn(o));
      }
      if (nn(value))
         return s(value);
      return super.getValue();
   }
}