Typescript utility type to parse route parameters

routeParameters.ts

type Tuple<X, Y> = [X, Y]
type Equal<X, Y> =
  (<T>() => T extends X ? 1 : 2) extends
  (<T>() => T extends Y ? 1 : 2) ? Tuple<true, Y> : Tuple<false, Y>
type Assert<T extends Tuple<true, any>> = T[1];// 

// P = collecting param names
// N = current param name 
// I = true if we are collecting a name 
type RouteParameters<R extends string, P extends string = never, N extends string = "", I extends boolean = false> =
  R extends `${infer C}${infer T}` 
  ? C extends ":"
    ? RouteParameters<T, P, N, true>
    : C extends "/" | "." | "-"
      ? I extends true
        ? RouteParameters<T, P|N, "", false>
        : RouteParameters<T, P, N, I>
      : I extends true
        ? RouteParameters<T, P, `${N}${C}`, I>
        : RouteParameters<T, P, N, I>
  : R extends `${infer C}`
    ? C extends ""
      ? I extends true 
        ? {[K in P | `${C}${N}`]: string}
        : {[K in P]: string}
      : {[K in P]: string}
    : {[K in P]: string}

type tests = [
  Assert<Equal<{}, RouteParameters<"">>>,
  Assert<Equal<{}, RouteParameters<"/foo">>>,
  Assert<Equal<{}, RouteParameters<"/foo/bar">>>,
  Assert<Equal<{foo: string}, RouteParameters<"/:foo">>>,
  Assert<Equal<{foo: string}, RouteParameters<"/:foo/">>>,
  Assert<Equal<{foo: string}, RouteParameters<"/:foo/bar">>>,
  Assert<Equal<{foo: string}, RouteParameters<"/bar/:foo">>>,
  Assert<Equal<{foo: string}, RouteParameters<"/bar/:foo/baz">>>,
  Assert<Equal<{foo: string, bar: string}, RouteParameters<"/:foo/:bar">>>,
  Assert<Equal<{foo: string, bar: string, baz: string}, RouteParameters<"/:foo/:bar/:baz">>>,
  Assert<Equal<{userId: string, bookId: string}, RouteParameters<"/users/:userId/books/:bookId">>>,
  Assert<Equal<{from: string, to: string}, RouteParameters<"/flights/:from-:to">>>,
  Assert<Equal<{genus: string, species: string}, RouteParameters<"/plantae/:genus.:species">>>,
];