io.zeebe.model.bpmn.traversal.ModelWalker Maven / Gradle / Ivy

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/*
 * Copyright © 2017 camunda services GmbH ([email protected])
 *
 * 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 io.zeebe.model.bpmn.traversal;

import io.zeebe.model.bpmn.BpmnModelInstance;
import io.zeebe.model.bpmn.impl.BpmnModelInstanceImpl;
import io.zeebe.model.bpmn.instance.BpmnModelElementInstance;
import io.zeebe.model.bpmn.instance.Definitions;
import java.util.Collection;
import java.util.Deque;
import java.util.LinkedList;
import org.camunda.bpm.model.xml.impl.util.ModelUtil;

/**
 * Walks the elements of a {@link BpmnModelInstance} and invokes the provided {@link
 * ModelElementVisitor} for every element.
 *
 * The following order is guaranteed (anything that is not listed here is not guaranteed):
 *
 * 

 *   An element is visited only after its parent has been visited (top-down)
 *   
An element's child is visisted before any not yet visited sibling (depth-first)
 * 
 *
 * We can add more constraints to this as we see fit (e.g. certain BPMN elements in the same
 * scope can be visited in a defined order to make transformation more convenient)
 *
 * Depth-first is nice for transformation so we can have some kind of stack with transformation
 * state.
 */
public class ModelWalker {

  private BpmnModelInstanceImpl modelInstance;
  private Deque elementsToVisit = new LinkedList<>();

  public ModelWalker(BpmnModelInstance modelInstance) {
    this.modelInstance = (BpmnModelInstanceImpl) modelInstance;
  }

  public void walk(ModelElementVisitor visitor) {
    final Definitions rootElement = modelInstance.getDefinitions();

    elementsToVisit.add(rootElement); // top-down

    BpmnModelElementInstance currentElement;
    while ((currentElement = elementsToVisit.poll()) != null) {
      visitor.visit(currentElement);
      final Collection children = getChildElements(currentElement);
      children.forEach(c -> elementsToVisit.addFirst(c)); // depth-first
    }
  }

  private Collection getChildElements(BpmnModelElementInstance element) {
    return ModelUtil.getModelElementCollection(
        element.getDomElement().getChildElements(), modelInstance);
  }
}