silverstripe-userforms/code/model/editableformfields/EditableFieldGroupEnd.php

<?php

/**
 * Specifies that this ends a group of fields
 */
class EditableFieldGroupEnd extends EditableFormField
{

    private static $belongs_to = array(
        'Group' => 'EditableFieldGroup'
    );

    /**
     * Disable selection of group class
     *
     * @config
     * @var bool
     */
    private static $hidden = true;

    /**
     * Non-data type
     *
     * @config
     * @var bool
     */
    private static $literal = true;

    public function getCMSTitle()
    {
        $group = $this->Group();
        return _t(
            'EditableFieldGroupEnd.FIELD_GROUP_END',
            '{group} end',
            array(
                'group' => ($group && $group->exists()) ? $group->CMSTitle : 'Group'
            )
        );
    }

    public function getCMSFields()
    {
        $fields = parent::getCMSFields();
        $fields->removeByName(array('MergeField', 'Default', 'Validation', 'DisplayRules'));
        return $fields;
    }

    public function getInlineClassnameField($column, $fieldClasses)
    {
        return new LabelField($column, $this->CMSTitle);
    }

    public function getInlineTitleField($column)
    {
        return HiddenField::create($column);
    }

    public function getFormField()
    {
        return null;
    }

    public function showInReports()
    {
        return false;
    }

    public function onAfterWrite()
    {
        parent::onAfterWrite();

        // If this is not attached to a group, find the first group prior to this
        // with no end attached
        $group = $this->Group();
        if (!($group && $group->exists()) && $this->ParentID) {
            $group = EditableFieldGroup::get()
                ->filter(array(
                    'ParentID' => $this->ParentID,
                    'Sort:LessThanOrEqual' => $this->Sort
                ))
                ->where('"EditableFieldGroup"."EndID" IS NULL OR "EditableFieldGroup"."EndID" = 0')
                ->sort('"Sort" DESC')
                ->first();

            // When a group is found, attach it to this end
            if ($group) {
                $group->EndID = $this->ID;
                $group->write();
            }
        }
    }

    protected function onAfterDelete()
    {
        parent::onAfterDelete();

        // Delete group
        if (($group = $this->Group()) && $group->exists()) {
            $group->delete();
        }
    }
}