import { DeepRequired } from './types.cjs';

/**
 * Deep merges 2 objects. Properties from the second parameter are applied to the first.
 * @remark `overwrites` is also mutated!
 * @remark If the value of a key in `overwrites` is `undefined` then the value of that same key in `base` is used instead!
 * @remark This is essentially `{ ...base, ...overwrites }` but recursively
 * @param base Base object
 * @param overwrites Overwrites to apply
 * @example
 * ```typescript
 * const base = { a: 0, b: 1 };
 * const overwrites = {}; // will be { a: 0, b: 1 } after merge
 * mergeDefault(base, overwrites) // { a: 0, b: 1 }
 * ```
 * @example
 * ```typescript
 * const base = { a: 0, b: 1 };
 * const overwrites = { a: 2, i: 3 };
 * mergeDefault(base, overwrites) // { a: 2, i: 3, b: 1 };
 * ```
 * @example
 * ```typescript
 * const base = { a: 0, b: 1 };
 * const overwrites = { a: null };
 * mergeDefault(base, overwrites) // { a: null, b: 1 };
 * ```
 * @example
 * ```typescript
 * const base = { a: 0, b: 1 };
 * const overwrites = { a: undefined };
 * mergeDefault(base, overwrites) // { a: 0, b: 1 };
 * ```
 * @example
 * ```typescript
 * const base = { a: null };
 * const overwrites = { a: { b: 5 } };
 * mergeDefault(base, overwrites) // { a: { b: 5 } };
 * ```
 */
declare function mergeDefault<A extends object, B extends Partial<A>>(base: A, overwrites?: B): DeepRequired<A & B>;

export { mergeDefault };