Division made in TS types

division.ts

// Multiplication comes from this issue:  https://github.com/type-challenges/type-challenges/issues/5814

type Reverse<A> =
  `${A}` extends `${infer AH}${infer AT}`
    ? `${Reverse<AT>}${AH}` : A

type Digs = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
type DigsNext<I = Digs, R = {}> =
  I extends [infer Head, infer Next, ...infer Tail]
    ? DigsNext<[Next, ...Tail], R & Record<Head, Next>>
    : { [K in keyof R]: R[K] }
type DigsPrev = { [K in keyof DigsNext as DigsNext[K]]: K }

type AddOne<A> =
  A extends `${infer AH}${infer AT}`
    ? AH extends '9' ? `0${AddOne<AT>}` : `${DigsNext[AH]}${AT}`
    : `1`
type SubOne<A> =
  A extends `${infer AH}${infer AT}`
    ? AH extends '0' ? `9${SubOne<AT>}` : `${DigsPrev[AH]}${AT}`
    : never
type Add<A, B> =
  A extends `${infer AH}${infer AT}` ?
    B extends `${infer BH}${infer BT}`
      ? BH extends '0' ? `${AH}${Add<AT, BT>}` : Add<AddOne<A>, SubOne<B>>
      : A : B


type Mul<A, B, R = '0'> =
  A extends '0' ? R :
    B extends '0' ? R :
      A extends `${infer AH}${infer AT}`
        ? AH extends '0' ? Mul<AT, `0${B}`, R> : Mul<SubOne<A>, B, Add<R, B>>
        : R

type Multiply<A extends string | number | bigint, B extends string | number | bigint> =
  Reverse<Mul<Reverse<A>, Reverse<B>>>
type GreaterThan<
  T extends number,
  U extends number,
  C extends unknown[] = []
  > =
  T extends U
    ? false
    : C['length'] extends T
      ? false
      : C['length'] extends U
        ? true
        : GreaterThan<T, U, [...C, 1]>;

type ToNumber<
  S extends string,
  L extends number[] = []
  > =
  `${L['length']}` extends S
    ? L['length']
    : ToNumber<S, [...L, 0]>;

type Sub<
  A extends string,
  B extends string,
  R extends string = "0"
  > =
  B extends R
      ? A
      : Sub<SubOne<A>, B, AddOne<R>>;


const sub: Sub<"5", "2"> =  "3"
const sub: Sub<"9", "8"> =  "1"
const sub: Sub<"8", "4"> =  "4"


type Division<
  W extends string,
  D extends string,
  Q extends string = '0'
  > =
   W extends '0'
      ? Q
      : Division<Sub<W, D>, D, AddOne<Q>>

const div: Division<"2", "2"> =  "1"
const div: Division<"4", "2"> =  "2"
const div: Division<"8", "2"> = "4"
const div: Division<"9", "3"> = "3"