feat(nodes): Add PositionFunc as node position type

* Allows position to be set relative to another node

package/src/types/node.ts

@@ -10,13 +10,17 @@ export type NodeHandleBounds = {
   target?: HandleElement[]
 }
 
-type WidthHeight = number | `${`parent` | string}(${`+` | `-`}${number})`
+type PositionFunc = <Data = ElementData>(
+  node: GraphNode<Data>,
+  currNodes: GraphNode<Data>[],
+  parentNode: GraphNode<Data>,
+) => XYPosition
 type WidthFunc = <Data = ElementData>(node: GraphNode<Data>) => number | string | void
 type HeightFunc = <Data = ElementData>(node: GraphNode<Data>) => number | string | void
 
 export interface Node<Data = ElementData> extends Element<Data> {
-  /** node position x, y */
-  position: XYPosition
+  /** initial node position x, y */
+  position: XYPosition | PositionFunc
   /** node type, can be a default type or a custom type */
   type?: keyof DefaultNodeTypes | string
   /** handle position */
@@ -56,6 +60,8 @@ export interface Node<Data = ElementData> extends Element<Data> {
 }
 
 export interface GraphNode<Data = ElementData> extends Node<Data> {
+  /** current node position x, y */
+  position: XYPosition
   /** absolute position in relation to parent elements + z-index */
   computedPosition: XYZPosition
   handleBounds: NodeHandleBounds