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) {
            $value = isset($this->value[$key]) ? $this->value[$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 $key
     *   Property name or index of the element.
     *
     * @return \Drupal\Core\TypedData\DataDefinitionInterface
     */
    protected abstract function getElementDefinition($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 isset($this->value) ? $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 a type definition array and
     * actual configuration data.
     *
     * @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;
    }

}