import { Pretty } from './Pretty.js';
import './Function.js';

/**
 * Make properties of T optionally `undefined`. This type is similar to `Partial` but
 * but the property must be present in T. It's also possible to specify which properties
 * should be made optional.
 *
 * @template T The type to make optional.
 * @template K The keys of T to make optional. If not provided, all keys are made optional.
 * @returns A new type with all properties of T optionally `undefined`
 * @example
 *
 * // Make all properties of T optionally `undefined`
 * Optional<{ a: string, b: number }> // { a: string | undefined, b: number | undefined }
 *
 * // Make some properties of T optionally `undefined`
 * Optional<{ a: string, b: number }, 'a'> // { a: string | undefined, b: number }
 */
type Optional<T, K extends keyof T = keyof T> = Pretty<{
    [P in Exclude<keyof T, K>]: T[P];
} & {
    [P in K]: T[P] | undefined;
}>;

export type { Optional };