class SubformState

class SubformState extends FormStateDecoratorBase implements SubformStateInterface {
    use FormStateValuesTrait;
    
    /**
     * The parent form.
     *
     * @var mixed[]
     */
    protected $parentForm;
    
    /**
     * The subform.
     *
     * @var mixed[]
     */
    protected $subform;
    
    /**
     * Constructs a new instance.
     *
     * @param mixed[] $subform
     *   The subform for which to create a form state.
     * @param mixed[] $parent_form
     *   The subform's parent form.
     * @param \Drupal\Core\Form\FormStateInterface $parent_form_state
     *   The parent form state.
     */
    protected function __construct(array &$subform, array &$parent_form, FormStateInterface $parent_form_state) {
        $this->decoratedFormState = $parent_form_state;
        $this->parentForm = $parent_form;
        $this->subform = $subform;
    }
    
    /**
     * Creates a new instance for a subform.
     *
     * @param mixed[] $subform
     *   The subform for which to create a form state.
     * @param mixed[] $parent_form
     *   The subform's parent form.
     * @param \Drupal\Core\Form\FormStateInterface $parent_form_state
     *   The parent form state.
     *
     * @return static
     */
    public static function createForSubform(array &$subform, array &$parent_form, FormStateInterface $parent_form_state) {
        return new static($subform, $parent_form, $parent_form_state);
    }
    
    /**
     * Gets the subform's parents relative to its parent form.
     *
     * @param string $property
     *   The property name (#parents or #array_parents).
     *
     * @return mixed
     *
     * @throws \InvalidArgumentException
     *   Thrown when the requested property does not exist.
     * @throws \UnexpectedValueException
     *   Thrown when the subform is not contained by the given parent form.
     */
    protected function getParents($property) {
        foreach ([
            $this->subform,
            $this->parentForm,
        ] as $form) {
            if (!isset($form[$property]) || !is_array($form[$property])) {
                throw new \RuntimeException(sprintf('The subform and parent form must contain the %s property, which must be an array. Try calling this method from a #process callback instead.', $property));
            }
        }
        $relative_subform_parents = $this->subform[$property];
        // Remove all of the subform's parents that are also the parent form's
        // parents, so we are left with the parents relative to the parent form.
        foreach ($this->parentForm[$property] as $parent_form_parent) {
            if ($parent_form_parent !== $relative_subform_parents[0]) {
                // The parent form's parents are the subform's parents as well. If we
                // find no match, that means the given subform is not contained by the
                // given parent form.
                throw new \UnexpectedValueException('The subform is not contained by the given parent form.');
            }
            array_shift($relative_subform_parents);
        }
        return $relative_subform_parents;
    }
    
    /**
     * {@inheritdoc}
     */
    public function &getValues() {
        $exists = NULL;
        $values =& NestedArray::getValue(parent::getValues(), $this->getParents('#parents'), $exists);
        if (!$exists) {
            $values = [];
        }
        elseif (!is_array($values)) {
            throw new \UnexpectedValueException('The form state values do not belong to the subform.');
        }
        return $values;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCompleteFormState() {
        return $this->decoratedFormState instanceof SubformStateInterface ? $this->decoratedFormState
            ->getCompleteFormState() : $this->decoratedFormState;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setLimitValidationErrors($limit_validation_errors) {
        if (is_array($limit_validation_errors)) {
            $limit_validation_errors = array_merge($this->getParents('#parents'), $limit_validation_errors);
        }
        return parent::setLimitValidationErrors($limit_validation_errors);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getLimitValidationErrors() {
        $limit_validation_errors = parent::getLimitValidationErrors();
        if (is_array($limit_validation_errors)) {
            return array_slice($limit_validation_errors, count($this->getParents('#parents')));
        }
        return $limit_validation_errors;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setErrorByName($name, $message = '') {
        $parents = $this->subform['#array_parents'];
        $parents[] = $name;
        $name = implode('][', $parents);
        parent::setErrorByName($name, $message);
        return $this;
    }

}