/*
    * 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 static com.linecorp.centraldogma.internal.jsonpatch.JsonPatchUtil.encodeSegment;
  import static java.util.Objects.requireNonNull;
  
  import java.io.IOException;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.TreeSet;
  
  import com.fasterxml.jackson.annotation.JsonCreator;
  import com.fasterxml.jackson.core.JsonGenerator;
  import com.fasterxml.jackson.core.JsonPointer;
  import com.fasterxml.jackson.databind.JsonMappingException;
  import com.fasterxml.jackson.databind.JsonNode;
  import com.fasterxml.jackson.databind.JsonSerializable;
  import com.fasterxml.jackson.databind.SerializerProvider;
  import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
  import com.fasterxml.jackson.databind.node.ArrayNode;
  import com.fasterxml.jackson.databind.node.JsonNodeType;
  import com.fasterxml.jackson.databind.node.ObjectNode;
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.base.Equivalence;
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.Iterators;
  import com.google.common.collect.Sets;
  
  import com.linecorp.centraldogma.internal.Jackson;
  
  /**
   * Implementation of JSON Patch.
   *
   * <p><a href="https://tools.ietf.org/html/draft-ietf-appsawg-json-patch-10">JSON
   * Patch</a>, as its name implies, is an IETF draft describing a mechanism to
   * apply a patch to any JSON value. This implementation covers all operations
   * according to the specification; however, there are some subtle differences
   * with regards to some operations which are covered in these operations'
   * respective documentation.</p>
   *
   * <p>An example of a JSON Patch is as follows:</p>
   *
   * <pre>
   *     [
   *         {
   *             "op": "add",
   *             "path": "/-",
   *             "value": {
   *                 "productId": 19,
   *                 "name": "Duvel",
   *                 "type": "beer"
   *             }
   *         }
   *     ]
   * </pre>
   *
   * <p>This patch contains a single operation which adds an item at the end of
   * an array. A JSON Patch can contain more than one operation; in this case, all
   * operations are applied to the input JSON value in their order of appearance,
   * until all operations are applied or an error condition is encountered.</p>
   *
   * <p>The main point where this implementation differs from the specification
   * is initial JSON parsing. The draft says:</p>
  *
  * <pre>
  *     Operation objects MUST have exactly one "op" member
  * </pre>
  *
  * <p>and:</p>
  *
  * <pre>
  *     Additionally, operation objects MUST have exactly one "path" member.
  * </pre>
  *
  * <p>However, obeying these to the letter forces constraints on the JSON
  * <b>parser</b>. Here, these constraints are not enforced, which means:</p>
  *
  * <pre>
  *     [ { "op": "add", "op": "remove", "path": "/x" } ]
  * </pre>
  *
  * <p>is parsed (as a {@code remove} operation, since it appears last).</p>
  *
  * <p><b>IMPORTANT NOTE:</b> the JSON Patch is supposed to be VALID when the
  * constructor for this class ({@link JsonPatch#fromJson(JsonNode)} is used.</p>
  */
 public final class JsonPatch implements JsonSerializable {
 
     private static final Equivalence<JsonNode> EQUIVALENCE = JsonNumEquals.getInstance();
     private static final JsonPointer EMPTY_JSON_POINTER = JsonPointer.compile("");
     private static final JsonPointer END_OF_ARRAY_POINTER = JsonPointer.compile("/-");
 
     /**
      * Static factory method to build a JSON Patch out of a JSON representation.
      *
      * @param node the JSON representation of the generated JSON Patch
      * @return a JSON Patch
      * @throws IOException input is not a valid JSON patch
      * @throws NullPointerException input is null
      */
     public static JsonPatch fromJson(final JsonNode node) throws IOException {
         requireNonNull(node, "node");
         try {
             return Jackson.treeToValue(node, JsonPatch.class);
         } catch (JsonMappingException e) {
             throw new JsonPatchException("invalid JSON patch", e);
         }
     }
 
     /**
      * Generates a JSON patch for transforming the source node into the target node.
      *
      * @param source the node to be patched
      * @param target the expected result after applying the patch
      * @param replaceMode the replace mode to be used
      * @return the patch as a {@link JsonPatch}
      */
     public static JsonPatch generate(final JsonNode source, final JsonNode target, ReplaceMode replaceMode) {
         requireNonNull(source, "source");
         requireNonNull(target, "target");
         final DiffProcessor processor = new DiffProcessor(replaceMode, () -> unchangedValues(source, target));
         generateDiffs(processor, EMPTY_JSON_POINTER, source, target);
         return processor.getPatch();
     }
 
     private static void generateDiffs(final DiffProcessor processor, final JsonPointer pointer,
                                       final JsonNode source, final JsonNode target) {
 
         if (EQUIVALENCE.equivalent(source, target)) {
             return;
         }
 
         final JsonNodeType sourceType = source.getNodeType();
         final JsonNodeType targetType = target.getNodeType();
 
         /*
          * Node types differ: generate a replacement operation.
          */
         if (sourceType != targetType) {
             processor.valueReplaced(pointer, source, target);
             return;
         }
 
         /*
          * If we reach this point, it means that both nodes are the same type,
          * but are not equivalent.
          *
          * If this is not a container, generate a replace operation.
          */
         if (!source.isContainerNode()) {
             processor.valueReplaced(pointer, source, target);
             return;
         }
 
         /*
          * If we reach this point, both nodes are either objects or arrays;
          * delegate.
          */
         if (sourceType == JsonNodeType.OBJECT) {
             generateObjectDiffs(processor, pointer, (ObjectNode) source, (ObjectNode) target);
         } else {
             // array
             generateArrayDiffs(processor, pointer, (ArrayNode) source, (ArrayNode) target);
         }
     }
 
     private static void generateObjectDiffs(final DiffProcessor processor, final JsonPointer pointer,
                                             final ObjectNode source, final ObjectNode target) {
 
         final Set<String> sourceFields = new TreeSet<>();
         Iterators.addAll(sourceFields, source.fieldNames());
         final Set<String> targetFields = new TreeSet<>();
         Iterators.addAll(targetFields, target.fieldNames());
 
         for (final String field : Sets.difference(sourceFields, targetFields)) {
             processor.valueRemoved(pointer.append(JsonPointer.valueOf(encodeSegment(field))));
         }
 
         for (final String field : Sets.difference(targetFields, sourceFields)) {
             processor.valueAdded(pointer.append(JsonPointer.valueOf(encodeSegment(field))), target.get(field));
         }
 
         for (final String field : Sets.intersection(sourceFields, targetFields)) {
             generateDiffs(processor, pointer.append(JsonPointer.valueOf(encodeSegment(field))),
                           source.get(field), target.get(field));
         }
     }
 
     private static void generateArrayDiffs(final DiffProcessor processor, final JsonPointer pointer,
                                            final ArrayNode source, final ArrayNode target) {
         final int sourceSize = source.size();
         final int targetSize = target.size();
         final int size = Math.min(sourceSize, targetSize);
 
         /*
          * Source array is larger; in this case, elements are removed from the
          * target; the index of removal is always the original arrays's length.
          */
         for (int index = size; index < sourceSize; index++) {
             processor.valueRemoved(pointer.append(JsonPointer.valueOf("/" + size)));
         }
 
         for (int index = 0; index < size; index++) {
             generateDiffs(processor, pointer.append(JsonPointer.valueOf("/" + index)),
                           source.get(index), target.get(index));
         }
 
         // Deal with the destination array being larger...
         for (int index = size; index < targetSize; index++) {
             processor.valueAdded(pointer.append(END_OF_ARRAY_POINTER), target.get(index));
         }
     }
 
     @VisibleForTesting
     static Map<JsonPointer, JsonNode> unchangedValues(final JsonNode source, final JsonNode target) {
         final Map<JsonPointer, JsonNode> ret = new HashMap<>();
         computeUnchanged(ret, EMPTY_JSON_POINTER, source, target);
         return ret;
     }
 
     private static void computeUnchanged(final Map<JsonPointer, JsonNode> ret, final JsonPointer pointer,
                                          final JsonNode source, final JsonNode target) {
         if (EQUIVALENCE.equivalent(source, target)) {
             ret.put(pointer, target);
             return;
         }
 
         final JsonNodeType sourceType = source.getNodeType();
         final JsonNodeType targetType = target.getNodeType();
 
         if (sourceType != targetType) {
             return; // nothing in common
         }
 
         // We know they are both the same type, so...
 
         switch (sourceType) {
             case OBJECT:
                 computeUnchangedObject(ret, pointer, source, target);
                 break;
             case ARRAY:
                 computeUnchangedArray(ret, pointer, source, target);
                 break;
             default:
                 /* nothing */
         }
     }
 
     private static void computeUnchangedObject(final Map<JsonPointer, JsonNode> ret, final JsonPointer pointer,
                                                final JsonNode source, final JsonNode target) {
         final Iterator<String> sourceFields = source.fieldNames();
         while (sourceFields.hasNext()) {
             final String name = sourceFields.next();
             if (!target.has(name)) {
                 continue;
             }
             computeUnchanged(ret, pointer.append(JsonPointer.valueOf(encodeSegment(name))),
                              source.get(name), target.get(name));
         }
     }
 
     private static void computeUnchangedArray(final Map<JsonPointer, JsonNode> ret, final JsonPointer pointer,
                                               final JsonNode source, final JsonNode target) {
         final int size = Math.min(source.size(), target.size());
         for (int i = 0; i < size; i++) {
             computeUnchanged(ret, pointer.append(JsonPointer.valueOf("/" + i)),
                              source.get(i), target.get(i));
         }
     }
 
     /**
      * List of operations.
      */
     private final List<JsonPatchOperation> operations;
 
     /**
      * Creates a new instance.
      *
      * @param operations the list of operations for this patch
      * @see JsonPatchOperation
      */
     @JsonCreator
     JsonPatch(final List<JsonPatchOperation> operations) {
         this.operations = ImmutableList.copyOf(operations);
     }
 
     /**
      * Returns whether this patch is empty.
      */
     public boolean isEmpty() {
         return operations.isEmpty();
     }
 
     /**
      * Returns the list of operations.
      */
     public List<JsonPatchOperation> operations() {
         return operations;
     }
 
     /**
      * Applies this patch to a JSON value.
      *
      * @param node the value to apply the patch to
      * @return the patched JSON value
      * @throws JsonPatchException failed to apply patch
      * @throws NullPointerException input is null
      */
     public JsonNode apply(final JsonNode node) {
         requireNonNull(node, "node");
         JsonNode ret = node.deepCopy();
         for (final JsonPatchOperation operation : operations) {
             ret = operation.apply(ret);
         }
 
         return ret;
     }
 
     /**
      * Converts this patch into JSON.
      */
     public ArrayNode toJson() {
         return (ArrayNode) Jackson.valueToTree(this);
     }
 
     @Override
     public String toString() {
         return operations.toString();
     }
 
     @Override
     public void serialize(final JsonGenerator jgen, final SerializerProvider provider) throws IOException {
         jgen.writeStartArray();
         for (final JsonPatchOperation op : operations) {
             op.serialize(jgen, provider);
         }
         jgen.writeEndArray();
     }
 
     @Override
     public void serializeWithType(final JsonGenerator jgen,
                                   final SerializerProvider provider, final TypeSerializer typeSer)
             throws IOException {
         serialize(jgen, provider);
     }
 }