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Core YAML 1.2 parser and emitter for Java
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/*
 * Copyright (c) 2018, SnakeYAML
 *
 * Licensed 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.snakeyaml.engine.v2.composer;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import org.snakeyaml.engine.v2.api.LoadSettings;
import org.snakeyaml.engine.v2.comments.CommentEventsCollector;
import org.snakeyaml.engine.v2.comments.CommentLine;
import org.snakeyaml.engine.v2.comments.CommentType;
import org.snakeyaml.engine.v2.common.Anchor;
import org.snakeyaml.engine.v2.common.FlowStyle;
import org.snakeyaml.engine.v2.events.AliasEvent;
import org.snakeyaml.engine.v2.events.Event;
import org.snakeyaml.engine.v2.events.MappingStartEvent;
import org.snakeyaml.engine.v2.events.NodeEvent;
import org.snakeyaml.engine.v2.events.ScalarEvent;
import org.snakeyaml.engine.v2.events.SequenceStartEvent;
import org.snakeyaml.engine.v2.exceptions.ComposerException;
import org.snakeyaml.engine.v2.exceptions.Mark;
import org.snakeyaml.engine.v2.exceptions.YamlEngineException;
import org.snakeyaml.engine.v2.nodes.MappingNode;
import org.snakeyaml.engine.v2.nodes.Node;
import org.snakeyaml.engine.v2.nodes.NodeTuple;
import org.snakeyaml.engine.v2.nodes.NodeType;
import org.snakeyaml.engine.v2.nodes.ScalarNode;
import org.snakeyaml.engine.v2.nodes.SequenceNode;
import org.snakeyaml.engine.v2.nodes.Tag;
import org.snakeyaml.engine.v2.parser.Parser;
import org.snakeyaml.engine.v2.resolver.ScalarResolver;

/**
 * Creates a node graph from parser events.
 * 
 * Corresponds to the 'Composer' step as described in chapter 3.1.2 of the
 * YAML Specification.
 * 
 * It implements {@link Iterator} to get the stream of {@link Node}s from the input.
 */
public class Composer implements Iterator {

  /**
   * Event parser
   */
  protected final Parser parser;
  private final ScalarResolver scalarResolver;
  private final Map anchors;
  private final Set recursiveNodes;
  private final LoadSettings settings;
  private final CommentEventsCollector blockCommentsCollector;
  private final CommentEventsCollector inlineCommentsCollector;
  private int nonScalarAliasesCount = 0;

  /**
   * @param parser - the input
   * @param settings - configuration options
   * @deprecated use the other constructor with LoadSettings first
   */
  @Deprecated
  public Composer(Parser parser, LoadSettings settings) {
    this(settings, parser);
  }

  /**
   * Create
   *
   * @param settings - configuration options
   * @param parser - the input
   */
  public Composer(LoadSettings settings, Parser parser) {
    this.parser = parser;
    this.scalarResolver = settings.getSchema().getScalarResolver();
    this.settings = settings;
    this.anchors = new HashMap<>();
    this.recursiveNodes = new HashSet<>();
    this.blockCommentsCollector =
        new CommentEventsCollector(parser, CommentType.BLANK_LINE, CommentType.BLOCK);
    this.inlineCommentsCollector = new CommentEventsCollector(parser, CommentType.IN_LINE);
  }

  /**
   * Checks if further documents are available.
   *
   * @return true if there is at least one more document.
   */
  public boolean hasNext() {
    // Drop the STREAM-START event.
    if (parser.checkEvent(Event.ID.StreamStart)) {
      parser.next();
    }
    // If there are more documents available?
    return !parser.checkEvent(Event.ID.StreamEnd);
  }

  /**
   * Reads a document from a source that contains only one document.
   * 
   * If the stream contains more than one document an exception is thrown.
   * 
   *
   * @return The root node of the document or Optional.empty() if no document is
   *         available.
   */
  public Optional getSingleNode() {
    // Drop the STREAM-START event.
    parser.next();
    // Compose a document if the stream is not empty.
    Optional document = Optional.empty();
    if (!parser.checkEvent(Event.ID.StreamEnd)) {
      document = Optional.of(next());
    }
    // Ensure that the stream contains no more documents.
    if (!parser.checkEvent(Event.ID.StreamEnd)) {
      Event event = parser.next();
      Optional previousDocMark = document.flatMap(Node::getStartMark);
      throw new ComposerException("expected a single document in the stream", previousDocMark,
          "but found another document", event.getStartMark());
    }
    // Drop the STREAM-END event.
    parser.next();
    return document;
  }

  /**
   * Reads and composes the next document.
   *
   * @return The root node of the document or null if no more documents are available.
   */
  public Node next() {
    // Collect inter-document start comments
    blockCommentsCollector.collectEvents();
    if (parser.checkEvent(Event.ID.StreamEnd)) {
      List commentLines = blockCommentsCollector.consume();
      Optional startMark = commentLines.get(0).getStartMark();
      List children = Collections.emptyList();
      Node node = new MappingNode(Tag.COMMENT, false, children, FlowStyle.BLOCK, startMark,
          Optional.empty());
      node.setBlockComments(commentLines);
      return node;
    }
    // Drop the DOCUMENT-START event.
    parser.next();
    // Compose the root node.
    Node node = composeNode(Optional.empty());
    // Drop the DOCUMENT-END event.
    blockCommentsCollector.collectEvents();
    if (!blockCommentsCollector.isEmpty()) {
      node.setEndComments(blockCommentsCollector.consume());
    }
    parser.next();
    this.anchors.clear();
    this.recursiveNodes.clear();
    this.nonScalarAliasesCount = 0;
    return node;
  }


  private Node composeNode(Optional parent) {
    blockCommentsCollector.collectEvents();
    parent.ifPresent(recursiveNodes::add);// TODO add unit test for this line
    final Node node;
    if (parser.checkEvent(Event.ID.Alias)) {
      AliasEvent event = (AliasEvent) parser.next();
      Anchor anchor = event.getAlias();
      if (!anchors.containsKey(anchor)) {
        throw new ComposerException("found undefined alias " + anchor, event.getStartMark());
      }
      node = anchors.get(anchor);
      if (node.getNodeType() != NodeType.SCALAR) {
        this.nonScalarAliasesCount++;
        if (this.nonScalarAliasesCount > settings.getMaxAliasesForCollections()) {
          throw new YamlEngineException(
              "Number of aliases for non-scalar nodes exceeds the specified max="
                  + settings.getMaxAliasesForCollections());
        }
      }
      if (recursiveNodes.remove(node)) {
        node.setRecursive(true);
      }
      // drop comments, they can not be supported here
      blockCommentsCollector.consume();
      inlineCommentsCollector.collectEvents().consume();
    } else {
      NodeEvent event = (NodeEvent) parser.peekEvent();
      Optional anchor = event.getAnchor();
      // the check for duplicate anchors has been removed (issue 174)
      if (parser.checkEvent(Event.ID.Scalar)) {
        node = composeScalarNode(anchor, blockCommentsCollector.consume());
      } else if (parser.checkEvent(Event.ID.SequenceStart)) {
        node = composeSequenceNode(anchor);
      } else {
        node = composeMappingNode(anchor);
      }
    }
    parent.ifPresent(recursiveNodes::remove);// TODO add unit test for this line
    return node;
  }

  private void registerAnchor(Anchor anchor, Node node) {
    anchors.put(anchor, node);
    node.setAnchor(Optional.of(anchor));
  }

  /**
   * Create ScalarNode
   *
   * @param anchor - anchor if present
   * @param blockComments - comments before the Node
   * @return Node
   */
  protected Node composeScalarNode(Optional anchor, List blockComments) {
    ScalarEvent ev = (ScalarEvent) parser.next();
    Optional tag = ev.getTag();
    boolean resolved = false;
    Tag nodeTag;
    if (!tag.isPresent() || tag.get().equals("!")) {
      nodeTag = scalarResolver.resolve(ev.getValue(), ev.getImplicit().canOmitTagInPlainScalar());
      resolved = true;
    } else {
      nodeTag = new Tag(tag.get());
    }
    Node node = new ScalarNode(nodeTag, resolved, ev.getValue(), ev.getScalarStyle(),
        ev.getStartMark(), ev.getEndMark());
    anchor.ifPresent(a -> registerAnchor(a, node));
    node.setBlockComments(blockComments);
    node.setInLineComments(inlineCommentsCollector.collectEvents().consume());
    return node;
  }

  /**
   * Compose a sequence Node from the input starting with SequenceStartEvent
   *
   * @param anchor - anchor if present
   * @return parsed Node
   */
  protected SequenceNode composeSequenceNode(Optional anchor) {
    SequenceStartEvent startEvent = (SequenceStartEvent) parser.next();
    Optional tag = startEvent.getTag();
    Tag nodeTag;
    boolean resolved = false;
    if (!tag.isPresent() || tag.get().equals("!")) {
      nodeTag = Tag.SEQ;
      resolved = true;
    } else {
      nodeTag = new Tag(tag.get());
    }
    final ArrayList children = new ArrayList<>();
    SequenceNode node = new SequenceNode(nodeTag, resolved, children, startEvent.getFlowStyle(),
        startEvent.getStartMark(), Optional.empty());
    if (startEvent.isFlow()) {
      node.setBlockComments(blockCommentsCollector.consume());
    }
    anchor.ifPresent(a -> registerAnchor(a, node));
    while (!parser.checkEvent(Event.ID.SequenceEnd)) {
      blockCommentsCollector.collectEvents();
      if (parser.checkEvent(Event.ID.SequenceEnd)) {
        break;
      }
      children.add(composeNode(Optional.of(node)));
    }
    if (startEvent.isFlow()) {
      node.setInLineComments(inlineCommentsCollector.collectEvents().consume());
    }
    Event endEvent = parser.next();
    node.setEndMark(endEvent.getEndMark());
    inlineCommentsCollector.collectEvents();
    if (!inlineCommentsCollector.isEmpty()) {
      node.setInLineComments(inlineCommentsCollector.consume());
    }
    return node;
  }

  /**
   * Create mapping Node
   *
   * @param anchor - anchor if present
   * @return Node
   */
  protected Node composeMappingNode(Optional anchor) {
    MappingStartEvent startEvent = (MappingStartEvent) parser.next();
    Optional tag = startEvent.getTag();
    Tag nodeTag;
    boolean resolved = false;
    if (!tag.isPresent() || tag.get().equals("!")) {
      nodeTag = Tag.MAP;
      resolved = true;
    } else {
      nodeTag = new Tag(tag.get());
    }

    final List children = new ArrayList<>();
    MappingNode node = new MappingNode(nodeTag, resolved, children, startEvent.getFlowStyle(),
        startEvent.getStartMark(), Optional.empty());
    if (startEvent.isFlow()) {
      node.setBlockComments(blockCommentsCollector.consume());
    }
    anchor.ifPresent(a -> registerAnchor(a, node));
    while (!parser.checkEvent(Event.ID.MappingEnd)) {
      blockCommentsCollector.collectEvents();
      if (parser.checkEvent(Event.ID.MappingEnd)) {
        break;
      }
      composeMappingChildren(children, node);
    }
    if (startEvent.isFlow()) {
      node.setInLineComments(inlineCommentsCollector.collectEvents().consume());
    }
    Event endEvent = parser.next();
    node.setEndMark(endEvent.getEndMark());
    inlineCommentsCollector.collectEvents();
    if (!inlineCommentsCollector.isEmpty()) {
      node.setInLineComments(inlineCommentsCollector.consume());
    }
    return node;
  }

  /**
   * Add the provided Node to the children as the last child
   *
   * @param children - the list to be extended
   * @param node - the child to the children
   */
  protected void composeMappingChildren(List children, MappingNode node) {
    Node itemKey = composeKeyNode(node);
    Node itemValue = composeValueNode(node);
    children.add(new NodeTuple(itemKey, itemValue));
  }

  /**
   * To be able to override composeNode(node) which is a key
   *
   * @param node - the source
   * @return node
   */
  protected Node composeKeyNode(MappingNode node) {
    return composeNode(Optional.of(node));
  }

  /**
   * To be able to override composeNode(node) which is a value
   *
   * @param node - the source
   * @return node
   */
  protected Node composeValueNode(MappingNode node) {
    return composeNode(Optional.of(node));
  }
}