import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Fill<[], 0>, []>>,
  Expect<Equal<Fill<[], 0, 0, 3>, []>>,
  Expect<Equal<Fill<[1, 2, 3], 0, 0, 0>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], 0, 2, 2>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], 0>, [0, 0, 0]>>,
  Expect<Equal<Fill<[1, 2, 3], true>, [true, true, true]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 0, 1>, [true, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 1, 3>, [1, true, true]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 10, 0>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 10, 20>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 0, 10>, [true, true, true]>>,
]

type FillInternal<
  T extends unknown[],
  N,
  Start extends number = 0,
  End extends number = T['length'],
  Left extends unknown[] = [],
  Mid extends unknown[] = [],
  Right extends unknown[] = T,
> =
Right extends [infer Head, ...infer Tail]
  ? Left['length'] extends Start
    ? Mid['length'] extends End
      ? [...Mid, Head, ...Tail]
      : FillInternal<T, N, Start, End, Left, [...Mid, N], Tail>
    : FillInternal<T, N, Start, End, [...Left, Head], [...Left, Head], Tail>
  : [...Mid, ...Right]
;

type Fill<
  T extends unknown[],
  N,
  Start extends number = 0,
  End extends number = T['length'],
> = FillInternal<T, N, Start, End>
;