class ArrayElement

abstract class ArrayElement extends Element implements \IteratorAggregate, TypedConfigInterface, ComplexDataInterface {
  
  /**
   * Parsed elements.
   */
  protected $elements;
  
  /**
   * Gets valid configuration data keys.
   *
   * @return array
   *   Array of valid configuration data keys.
   */
  protected function getAllKeys() {
    return is_array($this->value) ? array_keys($this->value) : [];
  }
  
  /**
   * Builds an array of contained elements.
   *
   * @return \Drupal\Core\TypedData\TypedDataInterface[]
   *   An array of elements contained in this element.
   */
  protected function parse() {
    $elements = [];
    foreach ($this->getAllKeys() as $key) {
      $value = $this->value[$key] ?? NULL;
      $definition = $this->getElementDefinition($key);
      $elements[$key] = $this->createElement($definition, $value, $key);
    }
    return $elements;
  }
  
  /**
   * Gets data definition object for contained element.
   *
   * @param int|string $key
   *   Property name or index of the element.
   *
   * @return \Drupal\Core\TypedData\DataDefinitionInterface
   */
  abstract protected function getElementDefinition($key);
  
  /**
   * {@inheritdoc}
   */
  public function get($name) {
    $parts = explode('.', $name);
    $root_key = array_shift($parts);
    $elements = $this->getElements();
    if (isset($elements[$root_key])) {
      $element = $elements[$root_key];
      // If $property_name contained a dot recurse into the keys.
      while ($element && ($key = array_shift($parts)) !== NULL) {
        if ($element instanceof TypedConfigInterface) {
          $element = $element->get($key);
        }
        else {
          $element = NULL;
        }
      }
    }
    if (isset($element)) {
      return $element;
    }
    else {
      throw new \InvalidArgumentException("The configuration property {$name} doesn't exist.");
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function getElements() {
    if (!isset($this->elements)) {
      $this->elements = $this->parse();
    }
    return $this->elements;
  }
  
  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    return empty($this->value);
  }
  
  /**
   * {@inheritdoc}
   */
  public function toArray() {
    return $this->value ?? [];
  }
  
  /**
   * {@inheritdoc}
   */
  public function onChange($name) {
    // Notify the parent of changes.
    if (isset($this->parent)) {
      $this->parent
        ->onChange($this->name);
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function getIterator() {
    return new \ArrayIterator($this->getElements());
  }
  
  /**
   * Creates a contained typed configuration object.
   *
   * @param \Drupal\Core\TypedData\DataDefinitionInterface $definition
   *   The data definition object.
   * @param mixed $value
   *   (optional) The data value. If set, it has to match one of the supported
   *   data type format as documented for the data type classes.
   * @param string $key
   *   The key of the contained element.
   *
   * @return \Drupal\Core\TypedData\TypedDataInterface
   */
  protected function createElement($definition, $value, $key) {
    return $this->getTypedDataManager()
      ->create($definition, $value, $key, $this);
  }
  
  /**
   * Creates a new data definition object from an array and configuration.
   *
   * @param array $definition
   *   The base type definition array, for which a data definition should be
   *   created.
   * @param $value
   *   The value of the configuration element.
   * @param string $key
   *   The key of the contained element.
   *
   * @return \Drupal\Core\TypedData\DataDefinitionInterface
   */
  protected function buildDataDefinition($definition, $value, $key) {
    return $this->getTypedDataManager()
      ->buildDataDefinition($definition, $value, $key, $this);
  }
  
  /**
   * Determines if this element allows NULL as a value.
   *
   * @return bool
   *   TRUE if NULL is a valid value, FALSE otherwise.
   */
  public function isNullable() {
    return isset($this->definition['nullable']) && $this->definition['nullable'] == TRUE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function set($property_name, $value, $notify = TRUE) {
    $this->value[$property_name] = $value;
    // Config schema elements do not make use of notifications. Thus, we skip
    // notifying parents.
    return $this;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getProperties($include_computed = FALSE) {
    $properties = [];
    foreach (array_keys($this->value) as $name) {
      $properties[$name] = $this->get($name);
    }
    return $properties;
  }

}