UserFormValidator.php

<?php

namespace SilverStripe\UserForms\Extension;

use SilverStripe\Forms\RequiredFields;
use SilverStripe\UserForms\Model\EditableFormField\EditableFieldGroup;
use SilverStripe\UserForms\Model\EditableFormField\EditableFieldGroupEnd;
use SilverStripe\UserForms\Model\EditableFormField;
use SilverStripe\UserForms\Model\EditableFormField\EditableFormStep;

class UserFormValidator extends RequiredFields
{
    public function php($data)
    {
        if (!parent::php($data)) {
            return false;
        }

        // Skip unsaved records
        if (empty($data['ID']) || !is_numeric($data['ID'])) {
            return true;
        }

        $fields = EditableFormField::get()->filter('ParentID', $data['ID'])->sort('"Sort" ASC');

        // Current nesting
        $stack = array();
        $conditionalStep = false; // Is the current step conditional?
        foreach ($fields as $field) {
            if ($field instanceof EditableFormStep) {
                // Page at top level, or after another page is ok
                if (empty($stack) || (count($stack ?? []) === 1 && $stack[0] instanceof EditableFormStep)) {
                    $stack = array($field);
                    $conditionalStep = $field->DisplayRules()->count() > 0;
                    continue;
                }

                $this->validationError(
                    'FormFields',
                    _t(
                        __CLASS__.".UNEXPECTED_BREAK",
                        "Unexpected page break '{name}' inside nested field '{group}'",
                        array(
                            'name' => $field->CMSTitle,
                            'group' => end($stack)->CMSTitle
                        )
                    ),
                    'error'
                );
                return false;
            }

            // Validate no pages
            if (empty($stack)) {
                $this->validationError(
                    'FormFields',
                    _t(
                        __CLASS__.".NO_PAGE",
                        "Field '{name}' found before any pages",
                        array(
                            'name' => $field->CMSTitle
                        )
                    ),
                    'error'
                );
                return false;
            }

            // Nest field group
            if ($field instanceof EditableFieldGroup) {
                $stack[] = $field;
                continue;
            }

            // Unnest field group
            if ($field instanceof EditableFieldGroupEnd) {
                $top = end($stack);

                // Check that the top is a group at all
                if (!$top instanceof EditableFieldGroup) {
                    $this->validationError(
                        'FormFields',
                        _t(
                            __CLASS__.".UNEXPECTED_GROUP_END",
                            "'{name}' found without a matching group",
                            array(
                                'name' => $field->CMSTitle
                            )
                        ),
                        'error'
                    );
                    return false;
                }

                // Check that the top is the right group
                if ($top->EndID != $field->ID) {
                    $this->validationError(
                        'FormFields',
                        _t(
                            __CLASS__.".WRONG_GROUP_END",
                            "'{name}' found closes the wrong group '{group}'",
                            array(
                                'name' => $field->CMSTitle,
                                'group' => $top->CMSTitle
                            )
                        ),
                        'error'
                    );
                    return false;
                }

                // Unnest group
                array_pop($stack);
            }

            // Normal field type
            if ($conditionalStep && $field->Required) {
                $this->validationError(
                    'FormFields',
                    _t(
                        __CLASS__.".CONDITIONAL_REQUIRED",
                        "Required field '{name}' cannot be placed within a conditional page",
                        array(
                            'name' => $field->CMSTitle
                        )
                    ),
                    'error'
                );
                return false;
            }
        }

        return true;
    }
}