/*
 * 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.commons.http;

import static org.apache.juneau.commons.utils.Shorts.*;
import static org.apache.juneau.commons.utils.StringUtils.*;

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

import org.apache.juneau.commons.bean.*;
import org.apache.juneau.commons.collections.*;

/**
 * A parsed <c>Accept</c> or similar header value.
 *
 * <p>
 * The returned media ranges are sorted such that the most acceptable media is available at ordinal position
 * <js>'0'</js>, and the least acceptable at position n-1.
 *
 * <p>
 * The syntax expected to be found in the referenced <c>value</c> complies with the syntax described in
 * RFC2616, Section 14.1, as described below:
 * <p class='bcode'>
 *    Accept         = "Accept" ":"
 *                      #( media-range [ accept-params ] )
 *
 *    media-range    = ( "*\/*"
 *                      | ( type "/" "*" )
 *                      | ( type "/" subtype )
 *                      ) *( ";" parameter )
 *    accept-params  = ";" "q" "=" qvalue *( accept-extension )
 *    accept-extension = ";" token [ "=" ( token | quoted-string ) ]
 * </p>
 *
 * <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>
 */
@BeanIgnore
public class MediaRanges {

   /** Represents an empty media ranges object. */
   public static final MediaRanges EMPTY = new MediaRanges("");

   private static final Cache<String,MediaRanges> CACHE = Cache.of(String.class, MediaRanges.class).build();

   /**
    * Compares two MediaRanges for equality.
    *
    * <p>
    * The values are first compared according to <c>qValue</c> values.
    * Should those values be equal, the <c>type</c> is then lexicographically compared (case-insensitive) in
    * ascending order, with the <js>"*"</js> type demoted last in that order.
    * <c>MediaRanges</c> with the same type but different sub-types are compared - a more specific subtype is
    * promoted over the 'wildcard' subtype.
    * <c>MediaRanges</c> with the same types but with extensions are promoted over those same types with no
    * extensions.
    */
   private static final Comparator<MediaRange> RANGE_COMPARATOR = (o1, o2) -> {
      // Compare q-values.
      var qCompare = Float.compare(o2.getQValue(), o1.getQValue());
      if (qCompare != 0)
         return qCompare;

      // Compare media-types.
      // Note that '*' comes alphabetically before letters, so just do a reverse-alphabetical comparison.
      return o2.toString().compareTo(o1.toString());
   };

   /**
    * Returns a parsed <c>Accept</c> header value.
    *
    * @param value The raw <c>Accept</c> header value.  Can be <jk>null</jk> or empty (returns {@link #EMPTY}).
    * @return A parsed <c>Accept</c> header value.
    */
   public static MediaRanges of(String value) {
      return isEmpty(value) ? EMPTY : CACHE.get(value, () -> new MediaRanges(value));
   }

   private static HeaderElement[] parse(String value) {
      return HeaderValueParser.readElements(emptyIfNull(trim(value)));
   }

   private final MediaRange[] ranges;

   private final String string;

   /**
    * Constructor.
    *
    * @param e The parsed header value.
    */
   public MediaRanges(HeaderElement[] e) {

      ranges = new MediaRange[e.length];
      for (var i = 0; i < e.length; i++)
         ranges[i] = new MediaRange(e[i]);
      Arrays.sort(ranges, RANGE_COMPARATOR);

      this.string = ranges.length == 1 ? ranges[0].toString() : join(ranges, ',');
   }

   /**
    * Constructor.
    *
    * @param value The <c>Accept</c> header value.  Can be <jk>null</jk> (treated as an empty string).
    */
   public MediaRanges(String value) {
      this(parse(value));
   }

   /**
    * Performs an action on the media ranges that make up this object.
    *
    * @param action The action to perform.
    * @return This object.
    */
   public MediaRanges forEachRange(Consumer<MediaRange> action) {
      for (var r : ranges)
         action.accept(r);
      return this;
   }

   /**
    * Returns the {@link MediaRange} at the specified index.
    *
    * @param index The index position of the media range.
    * @return The {@link MediaRange} at the specified index or <jk>null</jk> if the index is out of range.
    */
   public MediaRange getRange(int index) {
      if (index < 0 || index >= ranges.length)
         return null;
      return ranges[index];
   }

   /**
    * Convenience method for searching through all of the subtypes of all the media ranges in this header for the
    * presence of a subtype fragment.
    *
    * <p>
    * For example, given the header <js>"text/json+activity"</js>, calling
    * <code>hasSubtypePart(<js>"activity"</js>)</code> returns <jk>true</jk>.
    *
    * @param part The media type subtype fragment.
    * @return <jk>true</jk> if subtype fragment exists.
    */
   public boolean hasSubtypePart(String part) {

      for (var mr : ranges)
         if (mr.getQValue() > 0 && mr.getSubTypes().indexOf(part) >= 0)
            return true;

      return false;
   }

   /**
    * Given a list of media types, returns the best match for this <c>Accept</c> header.
    *
    * <p>
    * Note that fuzzy matching is allowed on the media types where the <c>Accept</c> header may
    * contain additional subtype parts.
    * <br>For example, given identical q-values and an <c>Accept</c> value of <js>"text/json+activity"</js>,
    * the media type <js>"text/json"</js> will match if <js>"text/json+activity"</js> or <js>"text/activity+json"</js>
    * isn't found.
    * <br>The purpose for this is to allow serializers to match when artifacts such as <c>id</c> properties are
    * present in the header.
    *
    * <p>
    * See <a class="doclink" href="https://www.w3.org/TR/activitypub/#retrieving-objects">ActivityPub / Retrieving Objects</a>
    *
    * @param mediaTypes The media types to match against.  Can be <jk>null</jk> (returns <c>-1</c>).
    * @return The index into the array of the best match, or <c>-1</c> if no suitable matches could be found.
    */
   public int match(List<? extends MediaType> mediaTypes) {
      if (string.isEmpty() || mediaTypes == null)
         return -1;

      int matchQuant = 0;
      int matchIndex = -1;
      var q = 0f;

      // Media ranges are ordered by 'q'.
      // So we only need to search until we've found a match.
      for (var mr : ranges) {
         var q2 = mr.getQValue();

         if (q2 < q || q2 == 0)
            break;

         for (var i = 0; i < mediaTypes.size(); i++) {
            var mt = mediaTypes.get(i);
            var matchQuant2 = mr.match(mt, false);

            // On an equally good match, prefer the candidate that declares itself with a higher q-value
            // (e.g. a serializer that only handles "application/jsonl;q=0.9" as a fallback).
            if (matchQuant2 > matchQuant || (matchQuant2 > 0 && matchQuant2 == matchQuant && q2 == q && qValueOf(mt) > qValueOf(mediaTypes.get(matchIndex)))) {
               matchIndex = i;
               matchQuant = matchQuant2;
               q = q2;
            }
         }
      }

      return matchIndex;
   }

   private static float qValueOf(MediaType mt) {
      return mt instanceof MediaRange mr ? mr.getQValue() : 1f;
   }

   /**
    * Returns the media ranges that make up this object.
    *
    * @return The media ranges that make up this object.
    */
   public List<MediaRange> toList() {
      return l(ranges);
   }

   @Override
   public boolean equals(Object o) {
      return o instanceof MediaRanges o2 && eq(this, o2, (x, y) -> eq(x.string, y.string));
   }

   @Override
   public int hashCode() {
      return Objects.hashCode(string);
   }

   @Override /* Overridden from Object */
   public String toString() {
      return string;
   }
}