/**
 * Flattens one level of nested objects before serializing to a query string.
 * Useful when a backend (e.g. Spring Boot Pageable / @ModelAttribute) expects
 * flat params (page=0&size=10) instead of Axios's default bracket notation
 * (pageable[page]=0&pageable[size]=10).
 *
 * Arrays at any level are repeated: sort=name,asc&sort=id,desc
 * null/undefined values are omitted.
 */
export const paramsSerializer = (params: Record<string, unknown>): string => {
  const parts: string[] = [];
  for (const [key, value] of Object.entries(params)) {
    if (value === undefined || value === null) continue;
    if (typeof value === 'object' && !Array.isArray(value)) {
      for (const [k, v] of Object.entries(value as Record<string, unknown>)) {
        if (v === undefined || v === null) continue;
        if (Array.isArray(v)) {
          for (const item of v)
            parts.push(
              `${encodeURIComponent(k)}=${encodeURIComponent(String(item))}`,
            );
        } else {
          parts.push(
            `${encodeURIComponent(k)}=${encodeURIComponent(String(v))}`,
          );
        }
      }
    } else if (Array.isArray(value)) {
      for (const item of value)
        parts.push(
          `${encodeURIComponent(key)}=${encodeURIComponent(String(item))}`,
        );
    } else {
      parts.push(
        `${encodeURIComponent(key)}=${encodeURIComponent(String(value))}`,
      );
    }
  }
  return parts.join('&');
};