/**
 * Recursively cleans empty string values ("" or whitespace only) to null in form submission payloads,
 * unless explicitly exempted by sendEmpty configuration.
 */
export function cleanEmptyStrings<T>(values: T, sendEmptyKeys?: Set<string> | string[]): T {
  const exemptions = sendEmptyKeys instanceof Set ? sendEmptyKeys : new Set(sendEmptyKeys || []);

  function clean(val: any, currentKey?: string): any {
    if (val === null || val === undefined) {
      return null;
    }

    if (typeof val === "string") {
      if (val.trim() === "") {
        return currentKey && exemptions.has(currentKey) ? "" : null;
      }
      return val;
    }

    if (Array.isArray(val)) {
      return val.map((item) => clean(item, currentKey));
    }

    if (typeof val === "object" && !(val instanceof Date) && !(val instanceof Blob) && !(val instanceof File)) {
      const cleanedObj: Record<string, any> = {};
      for (const [k, v] of Object.entries(val)) {
        cleanedObj[k] = clean(v, k);
      }
      return cleanedObj;
    }

    return val;
  }

  return clean(values);
}