text: 'use strict'
  var forEach = require('lodash/forEach')
  
  /**
   * A handler that implements a BPMN 2.0 property update
   * for business object lists which are not represented in the
   * diagram.
   *
   * This is useful in the context of the properties panel in
   * order to update child elements of elements visible in
   * the diagram.
   *
   * Example: perform an update of a specific event definition
   * of an intermediate event.
   *
   * @class
   * @constructor
   */
  function UpdateBusinessObjectListHandler(elementRegistry, bpmnFactory) {
    this._elementRegistry = elementRegistry
    this._bpmnFactory = bpmnFactory
  }
  
  UpdateBusinessObjectListHandler.$inject = ['elementRegistry', 'bpmnFactory']
  
  module.exports = UpdateBusinessObjectListHandler
  
  function ensureNotNull(prop, name) {
    if (!prop) {
      throw new Error(name + 'required')
    }
    return prop
  }
  
  // api /////////////////////////////////////////////
  
  /**
   * Updates a element under a provided parent.
   */
  UpdateBusinessObjectListHandler.prototype.execute = function (context) {
    var currentObject = ensureNotNull(context.currentObject, 'currentObject'),
      propertyName = ensureNotNull(context.propertyName, 'propertyName'),
      updatedObjectList = context.updatedObjectList,
      objectsToRemove = context.objectsToRemove || [],
      objectsToAdd = context.objectsToAdd || [],
      changed = [context.element], // this will not change any diagram-js elements
      referencePropertyName
  
    if (context.referencePropertyName) {
      referencePropertyName = context.referencePropertyName
    }
  
    var objectList = currentObject[propertyName]
    // adjust array reference in the parent business object
    context.previousList = currentObject[propertyName]
  
    if (updatedObjectList) {
      currentObject[propertyName] = updatedObjectList
    } else {
      var listCopy = []
      // remove all objects which should be removed
      forEach(objectList, function (object) {
        if (objectsToRemove.indexOf(object) === -1) {
          listCopy.push(object)
        }
      })
      // add all objects which should be added
      listCopy = listCopy.concat(objectsToAdd)
  
      // set property to new list
      if (listCopy.length > 0 || !referencePropertyName) {
        // as long as there are elements in the list update the list
        currentObject[propertyName] = listCopy
      } else if (referencePropertyName) {
        // remove the list when it is empty
        var parentObject = currentObject.$parent
        parentObject.set(referencePropertyName, undefined)
      }
    }
  
    context.changed = changed
  
    // indicate changed on objects affected by the update
    return changed
  }
  
  /**
   * Reverts the update
   *
   * @method  CreateBusinessObjectListHandler#revert
   *
   * @param {Object} context
   *
   * @return {djs.mode.Base} the updated element
   */
  UpdateBusinessObjectListHandler.prototype.revert = function (context) {
    var currentObject = context.currentObject,
      propertyName = context.propertyName,
      previousList = context.previousList,
      parentObject = currentObject.$parent
  
    if (context.referencePropertyName) {
      parentObject.set(context.referencePropertyName, currentObject)
    }
  
    // remove new element
    currentObject.set(propertyName, previousList)
  
    return context.changed
  }
  