Some thoughts on router types

RouterTypes.ts

**
 * A router needs to accept adding RouteDefinitions, which are routes with a name and
 * path, and potentially a 'fromArgs' and 'fromUrl' constructor, however these might be
 * possible to determine programmatically, so maybe not necessary.
 *
 * Uses:
 * * Determine which route we are on, and get any arguments for that route.
 * * Create a link to a route by supplying name and arguments.
 * * Potentially extend the route definition to do more? Preload? Do we want that in by default?
 */
type ArgsFromPath<TPath extends string> = Record<TPath, string>;

type RouteDefinition<
  TName extends string = string,
  TPath extends string = string
> = {
  name: TName;
  path: TPath;
  fromArgs: (args: ArgsFromPath<TPath>) => RouteInstantiation<TName, TPath>;
  fromUrl: (url: string) => RouteInstantiation<TName, TPath>;
};

type RouteInstantiation<TName extends string, TPath extends string> = {
  name: TName;
  path: TPath;
  url: string;
  args: ArgsFromPath<TPath>;
};

type Subscriber = (a: RouteInstantiation<string, string>) => void;

export type Router = {
  currentRoute: RouteInstantiation<string, string>;
  push: (route: RouteInstantiation<string, string>) => void;
  addRoutes: (...newRoutes: readonly RouteDefinition[]) => Router;
  removeRoutes: (...routeNames: readonly string[]) => Router;
  subscribe: (subscriber: Subscriber) => () => void;
};