/*
    * Copyright 2017 LINE Corporation
    *
    * LINE Corporation 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:
    *
    *   https://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.
   */
  /*
   * Copyright (c) 2014, Francis Galiegue (fgaliegue@gmail.com)
   *
   * This software is dual-licensed under:
   *
   * - the Lesser General Public License (LGPL) version 3.0 or, at your option, any
   *   later version;
   * - the Apache Software License (ASL) version 2.0.
   *
   * The text of this file and of both licenses is available at the root of this
   * project or, if you have the jar distribution, in directory META-INF/, under
   * the names LGPL-3.0.txt and ASL-2.0.txt respectively.
   *
   * Direct link to the sources:
   *
   * - LGPL 3.0: https://www.gnu.org/licenses/lgpl-3.0.txt
   * - ASL 2.0: https://www.apache.org/licenses/LICENSE-2.0.txt
   */
  
  package com.linecorp.centraldogma.internal.jsonpatch;
  
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Set;
  
  import com.fasterxml.jackson.databind.JsonNode;
  import com.fasterxml.jackson.databind.node.JsonNodeType;
  import com.google.common.base.Equivalence;
  import com.google.common.collect.Sets;
  
  /**
   * An {@link Equivalence} strategy for JSON Schema equality.
   *
   * <p>{@link JsonNode} does a pretty good job of obeying the  {@link
   * Object#equals(Object) equals()}/{@link Object#hashCode() hashCode()}
   * contract. And in fact, it does it too well for JSON Schema.</p>
   *
   * <p>For instance, it considers numeric nodes {@code 1} and {@code 1.0} to be
   * different nodes, which is true. But some IETF RFCs and drafts (among  them,
   * JSON Schema and JSON Patch) mandate that numeric JSON values be considered
   * equal if their mathematical value is the same. This class implements this
   * kind of equality.</p>
   */
  public final class JsonNumEquals extends Equivalence<JsonNode> {
  
      private static final Equivalence<JsonNode> INSTANCE = new JsonNumEquals();
  
      public static Equivalence<JsonNode> getInstance() {
          return INSTANCE;
      }
  
      private JsonNumEquals() {}
  
      @Override
      protected boolean doEquivalent(final JsonNode a, final JsonNode b) {
          /*
           * If both are numbers, delegate to the helper method
           */
          if (a.isNumber() && b.isNumber()) {
              return numEquals(a, b);
          }
  
          final JsonNodeType typeA = a.getNodeType();
          final JsonNodeType typeB = b.getNodeType();
  
          /*
           * If they are of different types, no dice
           */
          if (typeA != typeB) {
              return false;
          }
  
          /*
           * For all other primitive types than numbers, trust JsonNode
           */
          if (!a.isContainerNode()) {
              return a.equals(b);
          }
  
          /*
           * OK, so they are containers (either both arrays or objects due to the
           * test on types above). They are obviously not equal if they do not
           * have the same number of elements/members.
           */
         if (a.size() != b.size()) {
             return false;
         }
 
         /*
          * Delegate to the appropriate method according to their type.
          */
         return typeA == JsonNodeType.ARRAY ? arrayEquals(a, b) : objectEquals(a, b);
     }
 
     @Override
     protected int doHash(final JsonNode t) {
         /*
          * If this is a numeric node, we want the same hashcode for the same
          * mathematical values. Go with double, its range is good enough for
          * 99+% of use cases.
          */
         if (t.isNumber()) {
             return Double.valueOf(t.doubleValue()).hashCode();
         }
 
         /*
          * If this is a primitive type (other than numbers, handled above),
          * delegate to JsonNode.
          */
         if (!t.isContainerNode()) {
             return t.hashCode();
         }
 
         /*
          * The following hash calculations work, yes, but they are poor at best.
          * And probably slow, too.
          *
          * TODO: try and figure out those hash classes from Guava
          */
         int ret = 0;
 
         /*
          * If the container is empty, just return
          */
         if (t.size() == 0) {
             return ret;
         }
 
         /*
          * Array
          */
         if (t.isArray()) {
             for (final JsonNode element : t) {
                 ret = 31 * ret + doHash(element);
             }
             return ret;
         }
 
         /*
          * Not an array? An object.
          */
         final Iterator<Map.Entry<String, JsonNode>> iterator = t.fields();
 
         Map.Entry<String, JsonNode> entry;
 
         while (iterator.hasNext()) {
             entry = iterator.next();
             ret = 31 * ret + (entry.getKey().hashCode() ^ doHash(entry.getValue()));
         }
 
         return ret;
     }
 
     private static boolean numEquals(final JsonNode a, final JsonNode b) {
         /*
          * If both numbers are integers, delegate to JsonNode.
          */
         if (a.isIntegralNumber() && b.isIntegralNumber()) {
             return a.equals(b);
         }
 
         /*
          * Otherwise, compare decimal values.
          */
         return a.decimalValue().compareTo(b.decimalValue()) == 0;
     }
 
     private boolean arrayEquals(final JsonNode a, final JsonNode b) {
         /*
          * We are guaranteed here that arrays are the same size.
          */
         final int size = a.size();
 
         for (int i = 0; i < size; i++) {
             if (!doEquivalent(a.get(i), b.get(i))) {
                 return false;
             }
         }
 
         return true;
     }
 
     private boolean objectEquals(final JsonNode a, final JsonNode b) {
         /*
          * Grab the key set from the first node
          */
         final Set<String> keys = Sets.newHashSet(a.fieldNames());
 
         /*
          * Grab the key set from the second node, and see if both sets are the
          * same. If not, objects are not equal, no need to check for children.
          */
         final Set<String> set = Sets.newHashSet(b.fieldNames());
         if (!set.equals(keys)) {
             return false;
         }
 
         /*
          * Test each member individually.
          */
         for (final String key : keys) {
             if (!doEquivalent(a.get(key), b.get(key))) {
                 return false;
             }
         }
 
         return true;
     }
 }