type-plus
Version:
Provides additional types for TypeScript.
75 lines (70 loc) • 2.02 kB
text/typescript
import type { NeverType } from '../never/never_type.js'
import type { IsTuple } from '../tuple/tuple_type.js'
import type { IndexAt } from './array_index.js'
import type { ArrayType } from './array_type.js'
/**
* ⚗️ *transform*
*
* Splits array or tuple `A` into two at the specified `Index`.
*
* If the `Index` is out of bounds,
* it will set to the boundary value.
*
* It is the type level `splice()`.
*
* @example
* ```ts
* SplitAt<[1, 2, 3, 4, 5], 2> // [[1, 2], [3, 4, 5]]
* SplitAt<[1, 2, 3, 4, 5], -3> // [[1, 2], [3, 4, 5]]
*
* SplitAt<[1, 2, 3, 4, 5], 2, 2> // [[1, 2, 5], [3, 4]]
*
* SplitAt<[1, 2, 3, 4, 5], 2, 2, ['a', 'b']> // [[1, 2, 'a', 'b', 5], [3, 4]]
*
* // out of bound resets to boundary
* SplitAt<[1, 2, 3, 4, 5], 6> // [[1, 2, 3, 4, 5], []]
* SplitAt<[1, 2, 3, 4, 5], -6> // [[], [1, 2, 3, 4, 5]]
* ```
*/
export type SplitAt<
A extends unknown[],
Index extends number,
DeleteCount extends number | never = never,
Insert extends unknown[] | never = never
> = ArrayType<
A,
[A, A],
SplitAt._<A, [], [], IndexAt._<A, Index>, DeleteCount, Insert>
>
export namespace SplitAt {
export type _<
A extends unknown[],
B extends unknown[],
C extends unknown[],
Index extends number,
DeleteCount,
Insert extends unknown[],
> = 0 extends A['length']
? IsTuple<Insert, [[...Insert, ...B], C], [B, C]>
: (Index extends B['length']
? _D<A, B, C, DeleteCount, Insert>
: (A extends [infer Head, ...infer Tail]
? _<Tail, [...B, Head], [], Index, DeleteCount, Insert>
: 'unexpected: A does not extends [Head, ...Tail]'))
export type _D<
A extends unknown[],
B extends unknown[],
C extends unknown[],
DeleteCount,
Insert extends unknown[],
> = NeverType<
DeleteCount,
[B, A],
DeleteCount extends C['length']
? IsTuple<Insert, [[...B, ...Insert, ...A], C], [[...B, ...A], C]>
: (A extends [infer Head, ...infer Tail]
? _D<Tail, B, [...C, Head], DeleteCount, Insert>
: IsTuple<Insert, [[...Insert, ...B], C], [B, C]>
)
>
}