requirement-types.ts

/**
 * Wether the property is optional in the object or not.
 * 
 * @example ```
 * type Foo = PropertyRequirement<{ a: number }, 'a'>; // 'required'
 * type Bar = PropertyRequirement<{ b?: number }, 'b'>; // 'optional'
 * ```
 */
type PropertyRequirement<T, K extends keyof T> = Pick<T, K> extends Required<
  Pick<T, K>
>
  ? 'required'
  : 'optional';

/**
 * Wether any of the properties of the object is required.
 *
 * @example ```
 *  type Foo = ObjectRequirement<{ a: number; b: number }> // 'required'
 *  type Bar = ObjectRequirement<{ a: number; b?: number }> // 'required'
 *  type Baz = ObjectRequirement<{ a?: number; b?: number }> // 'optional'
 * ```
 */
type ObjectRequirement<T> = {
  [K in keyof T]-?: PropertyRequirement<T, K>;
}[keyof T] extends 'optional'
  ? 'optional'
  : { [K in keyof T]-?: PropertyRequirement<T, K> }[keyof T] extends
      | 'optional'
      | 'required'
  ? 'required'
  : 'required';