firefish/packages/backend/src/prelude/undefined-to-null.ts

// https://gist.github.com/tkrotoff/a6baf96eb6b61b445a9142e5555511a0
import type { Primitive } from "type-fest";

type NullToUndefined<T> = T extends null
	? undefined
	: T extends Primitive | Function | Date | RegExp
		? T
		: T extends Array<infer U>
			? Array<NullToUndefined<U>>
			: T extends Map<infer K, infer V>
				? Map<K, NullToUndefined<V>>
				: T extends Set<infer U>
					? Set<NullToUndefined<U>>
					: T extends object
						? { [K in keyof T]: NullToUndefined<T[K]> }
						: unknown;

type UndefinedToNull<T> = T extends undefined
	? null
	: T extends Primitive | Function | Date | RegExp
		? T
		: T extends Array<infer U>
			? Array<UndefinedToNull<U>>
			: T extends Map<infer K, infer V>
				? Map<K, UndefinedToNull<V>>
				: T extends Set<infer U>
					? Set<NullToUndefined<U>>
					: T extends object
						? { [K in keyof T]: UndefinedToNull<T[K]> }
						: unknown;

function _nullToUndefined<T>(obj: T): NullToUndefined<T> {
	if (obj === null) {
		return undefined as any;
	}

	if (typeof obj === "object") {
		if (obj instanceof Map) {
			obj.forEach((value, key) => obj.set(key, _nullToUndefined(value)));
		} else {
			for (const key in obj) {
				obj[key] = _nullToUndefined(obj[key]) as any;
			}
		}
	}

	return obj as any;
}

function _undefinedToNull<T>(obj: T): UndefinedToNull<T> {
	if (obj === undefined) {
		return null as any;
	}

	if (typeof obj === "object") {
		if (obj instanceof Map) {
			obj.forEach((value, key) => obj.set(key, _undefinedToNull(value)));
		} else {
			for (const key in obj) {
				obj[key] = _undefinedToNull(obj[key]) as any;
			}
		}
	}

	return obj as any;
}

/**
 * Recursively converts all undefined values to null.
 *
 * @param obj object to convert
 * @returns a copy of the object with all its undefined values converted to null
 */
export function undefinedToNull<T>(obj: T) {
	return _undefinedToNull(structuredClone(obj));
}