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();
		}
	}

}