216 - Slice

[JohnLi1999]

type NumberToTuple<T extends number, U extends 1[] = []> = U['length'] extends T
  ? U
  : NumberToTuple<T, [...U, 1]>;

type Subtract<A extends number, B extends number> = NumberToTuple<A> extends [
  ...NumberToTuple<B>,
  ...infer R
]
  ? R['length']
  : 0;

type ToNonNegativeIndex<
  Index extends number,
  Length extends number
> = `${Index}` extends `-${infer AbsIndex extends number}`
  ? Subtract<Length, AbsIndex>
  : Index;

type SliceWithNonNegativeIndices<
  Arr,
  Start,
  End,
  Index extends 1[] = [],
  Result extends unknown[] = []
> = End extends Index['length']
  ? Result
  : Arr extends [infer F, ...infer R]
  ? Start extends Index['length'] | 0
    ? SliceWithNonNegativeIndices<R, 0, End, [...Index, 1], [...Result, F]>
    : SliceWithNonNegativeIndices<R, Start, End, [...Index, 1], Result>
  : [];

type Slice<
  Arr extends unknown[],
  Start extends number = 0,
  End extends number = Arr['length']
> = SliceWithNonNegativeIndices<
  Arr,
  ToNonNegativeIndex<Start, Arr['length']>,
  ToNonNegativeIndex<End, Arr['length']>
>;