type-plus/ts/tuple/tuple_plus.pad_start.ts

Provides additional types for TypeScript.

/**
 * Pad `T` with `PadWith` at the start of the tuple.
 *
 * If the `MaxLength` is less than the length of the tuple,
 * the `Tuple` will be returned unchanged.
 *
 * ⚗️ *transform*
 *
 * @example
 * ```ts
 * PadStart<[1, 2, 3], 5, 0> // [0, 0, 1, 2, 3]
 *
 * // Ignore if MaxLength is less than the length of the tuple
 * PadStart<[1, 2, 3], 2> // [1, 2, 3]
 *
 * // Default to unknown
 * PadStart<[1, 2, 3], 5> // [unknown, unknown, 1, 2, 3]
 * ```
 */
export type PadStart<Tuple extends unknown[], MaxLength extends number, PadWith = unknown> = PadStart.Device<
	Tuple,
	MaxLength,
	PadWith,
	[]
>

export namespace PadStart {
	export type Device<
		Source extends unknown[],
		MaxLength extends number,
		PadWith,
		Result extends unknown[]
	> =
		Result['length'] extends MaxLength
		? (
			Source extends []
			? Result
			: (
				Source extends [...infer Head, infer Tail]
				? (
					[Tail, ...Result] extends infer R extends unknown[]
					? Device<Head, R['length'], PadWith, R>
					: never
				)
				: never
			)
		)
		: (
			Source extends []
			? Device<Source, MaxLength, PadWith, [PadWith, ...Result]>
			: (
				Source extends [...infer Head, infer Tail]
				? Device<Head, MaxLength, PadWith, [Tail, ...Result]>
				: Source
			)
		)

}