interface IHierarchicalScaleOptions {
  /**
   * ratio by which the distance between two elements shrinks the higher the level of the tree is. i.e. two two level bars have a distance of 1. two nested one just 0.75
   * @default 0.75
   */
  levelPercentage: number;
  /**
   * padding of the first collapse to the start of the x-axis
   * @default 25
   */
  padding: number;
  /**
   * position of the hierarchy label in expanded levels, null to disable
   * @default 'below'
   */
  hierarchyLabelPosition: 'below'|'above'|null;
  /**
   * positon of the hierarchy group label relative to the its children
   * @default 'between-first-and-second'
   */
  hierarchyGroupLabelPosition: 'center'|'first'|'last'|'between-first-and-second',

  /**
   * object of attributes that should be managed and extacted from the tree datastrutures such as `backgroundColor` for coloring individual bars
   * the object conainst the key and default value
   * @default {}
   */
  attributes: {[attribute: string]: any};
}

interface ILabelNode {
  /**
   * label
   */
  label: string;
  /**
   * defines whether this node is collapsed (false) or expanded (true) or focussed ('focus')
   * @default false
   */
  expand?: boolean | 'focus';
  /**
   * list of children
   */
  children?: ISubLabelNode[];
}

/**
 * a label entry can be a single string or a complex ILabelNode
 */
declare type ISubLabelNode = ILabelNode | string;

interface IValueNode<T> {
  /**
   * the actual value of this node
   */
  value: T;
  /**
   * list of children
   */
  children?: ISubValueNode<T>[];
}

/**
 * a value entry can be a single value or a complex IValueNode
 */
declare type ISubValueNode<T> = IValueNode<T> | T;