Demo Node structure

nodes.ts

type UUID = string;

interface BaseNode {
  uuid: UUID;
  path: string; // parent-uuid/uuid
  type: "node" | "section" | "group" | "text";
  allowedChildren?: ContentNodes; // Optional because the actual instances of Nodes do not need this
  children?: UUID[]; // not all Nodes have children
}

interface SectionNode extends BaseNode {
  type: "section";
  allowedChildren?: GroupNode | TextBlock; // Could be moved to ValidChildren instead
}

interface GroupNode extends BaseNode {
  type: "group";
  allowedChildren?: TextBlock; // Could be moved to ValidChildren instead
}

interface TextBlock extends BaseNode {
  type: "text";
  allowedChildren?: never; // Could be moved to ValidChildren instead
}

type ContentNodes = SectionNode | GroupNode | TextBlock;

export interface ValidChildren {
  section: SectionNode["allowedChildren"]; // GroupNode | TextBlock
  group: GroupNode["allowedChildren"]; // TextBlock
  text: TextBlock["allowedChildren"]; // never
}

type AssertValidChild<
  P extends ContentNodes,
  C extends ContentNodes
> = C extends ValidChildren[P["type"]]
  ? unknown
  : {
      "invalid child element for": P;
      allowedChildren: ValidChildren[P["type"]];
    };

const text: TextBlock = {
  uuid: '2345',
  path: '/section-123/group-1234/text-2345',
  type: 'text'
};

const group2: GroupNode = {
  uuid: '1235',
  path: '/section-123/group-1234',
  type: 'group',
  children: []
};

const group1: GroupNode = {
  uuid: '1234',
  path: '/section-123/group-1235',
  type: 'group',
  children: [text]
};

const section: SectionNode = {
  uuid: '123',
  path: '/section-123',
  type: 'section',
  children: [text, group1]
};

This is the start of our basic node structure (minus any data that actually means anything).

There is some additional work that allows a check of the allowed children.