/*
    * 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.maven.plugins.dependency.tree;
  
  import java.io.IOException;
  import java.io.UncheckedIOException;
  import java.io.Writer;
  import java.util.HashSet;
  import java.util.Set;
  
  import org.apache.maven.artifact.Artifact;
  import org.apache.maven.shared.dependency.graph.DependencyNode;
  import org.apache.maven.shared.dependency.graph.traversal.DependencyNodeVisitor;
  
  /**
   * A dependency node visitor that serializes visited nodes to a writer using the JSON format.
   */
  public class JsonDependencyNodeVisitor extends AbstractSerializingVisitor implements DependencyNodeVisitor {
  
      private String indentChar = " ";
  
      /**
       * Creates a new instance of {@link JsonDependencyNodeVisitor}. The writer will be used to write the output.
       *
       * @param writer  the writer to write to
       */
      public JsonDependencyNodeVisitor(Writer writer) {
          super(writer);
      }
  
      @Override
      public boolean visit(DependencyNode node) {
          try {
              if (node.getParent() == null || node.getParent() == node) {
                  writeRootNode(node);
              }
              return true;
          } catch (IOException e) {
              throw new UncheckedIOException("Failed to write JSON format output", e);
          }
      }
  
      /**
       * Writes the node to the writer. This method is recursive and will write all children nodes.
       *
       * @param node  the node to write
       * @throws IOException if an I/O error occurs while writing
       */
      private void writeRootNode(DependencyNode node) throws IOException {
          Set<DependencyNode> visited = new HashSet<>();
          int indent = 2;
          StringBuilder sb = new StringBuilder();
          sb.append("{").append(System.lineSeparator());
          writeNode(indent, node, sb, visited);
          sb.append("}").append(System.lineSeparator());
          writer.write(sb.toString());
          writer.flush();
      }
      /**
       * Appends the node and its children to the string builder.
       *
       * @param indent  the current indent level
       * @param node  the node to write
       * @param sb  the string builder to append to
       */
      private void writeNode(int indent, DependencyNode node, StringBuilder sb, Set<DependencyNode> visited) {
          if (visited.contains(node)) {
              // Circular dependency detected
              // Should an exception be thrown?
              return;
          }
          visited.add(node);
          appendNodeValues(sb, indent, node.getArtifact(), !node.getChildren().isEmpty());
          if (!node.getChildren().isEmpty()) {
              writeChildren(indent, node, sb, visited);
          }
      }
      /**
       * Writes the children of the node to the string builder. Each child of each node will be written recursively.
       *
       * @param indent  the current indent level
       * @param node  the node to write
       * @param sb  the string builder to append to
      */
     private void writeChildren(int indent, DependencyNode node, StringBuilder sb, Set<DependencyNode> visited) {
         sb.append(indent(indent)).append("\"children\": [").append(System.lineSeparator());
         indent += 2;
         for (int i = 0; i < node.getChildren().size(); i++) {
             DependencyNode child = node.getChildren().get(i);
             sb.append(indent(indent));
             sb.append("{").append(System.lineSeparator());
             writeNode(indent + 2, child, sb, visited);
             sb.append(indent(indent)).append("}");
             // we skip the comma for the last child
             if (i != node.getChildren().size() - 1) {
                 sb.append(",");
             }
             sb.append(System.lineSeparator());
         }
         sb.append(indent(indent)).append("]").append(System.lineSeparator());
     }
 
     @Override
     public boolean endVisit(DependencyNode node) {
         return true;
     }
     /**
      * Appends the artifact values to the string builder.
      *
      * @param sb  the string builder to append to
      * @param indent  the current indent level
      * @param artifact  the artifact to write
      * @param hasChildren  true if the artifact has children
      */
     private void appendNodeValues(StringBuilder sb, int indent, Artifact artifact, boolean hasChildren) {
         appendKeyValue(sb, indent, "groupId", artifact.getGroupId());
         appendKeyValue(sb, indent, "artifactId", artifact.getArtifactId());
         appendKeyValue(sb, indent, "version", artifact.getVersion());
         appendKeyValue(sb, indent, "type", artifact.getType());
         appendKeyValue(sb, indent, "scope", artifact.getScope());
         appendKeyValue(sb, indent, "classifier", artifact.getClassifier());
         if (hasChildren) {
             appendKeyValue(sb, indent, "optional", String.valueOf(artifact.isOptional()));
         } else {
             appendKeyWithoutComma(sb, indent, "optional", String.valueOf(artifact.isOptional()));
         }
     }
     /**
      * Appends a key value pair to the string builder.
      *
      * @param sb  the string builder to append to
      * @param indent  the current indent level
      * @param key  the key used as json key
      * @param value  the value used as json value
      */
     private void appendKeyValue(StringBuilder sb, int indent, String key, String value) {
         if (value == null) {
             value = "";
         }
 
         sb.append(indent(indent))
                 .append("\"")
                 .append(key)
                 .append("\"")
                 .append(":")
                 .append(indentChar)
                 .append("\"")
                 .append(value)
                 .append("\"")
                 .append(",")
                 .append(System.lineSeparator());
     }
     /**
      * Appends a key value pair to the string builder without a comma at the end. This is used for the last children of a node.
      *
      * @param sb  the string builder to append to
      * @param indent  the current indent level
      * @param key  the key used as json key
      * @param value  the value used as json value
      */
     private void appendKeyWithoutComma(StringBuilder sb, int indent, String key, String value) {
         if (value == null) {
             value = "";
         }
 
         sb.append(indent(indent))
                 .append("\"")
                 .append(key)
                 .append("\"")
                 .append(":")
                 .append(indentChar)
                 .append("\"")
                 .append(value)
                 .append("\"")
                 .append(System.lineSeparator());
     }
 
     /**
      * Returns a string of {@link #indentChar} for the indent level.
      *
      * @param indent  the number of indent levels
      * @return  the string of indent characters
      */
     private String indent(int indent) {
         if (indent < 1) {
             return "";
         }
 
         StringBuilder sb = new StringBuilder();
         for (int i = 0; i < indent; i++) {
             sb.append(indentChar);
         }
 
         return sb.toString();
     }
 }