/** Helpers for reading Next.js searchParams (Promise<Record<string, string | string[] | undefined>>). */
export type SP = Record<string, string | string[] | undefined>;

export function sp1(sp: SP, key: string): string | undefined {
  const v = sp[key];
  const s = Array.isArray(v) ? v[0] : v;
  return s && s.length ? s : undefined;
}

export function spNum(sp: SP, key: string): number | null {
  const s = sp1(sp, key);
  if (s === undefined) return null;
  const n = Number(s.replace(/[,$\s]/g, ''));
  return Number.isFinite(n) ? n : null;
}

export function spInt(sp: SP, key: string, fallback = 1): number {
  const n = spNum(sp, key);
  return n === null ? fallback : Math.max(1, Math.trunc(n));
}

export function spEnum<T extends string>(sp: SP, key: string, allowed: readonly T[], fallback: T): T {
  const s = sp1(sp, key);
  return s && (allowed as readonly string[]).includes(s) ? (s as T) : fallback;
}

export function pick(sp: SP, keys: string[]): Record<string, string | undefined> {
  const out: Record<string, string | undefined> = {};
  for (const k of keys) out[k] = sp1(sp, k);
  return out;
}

export function withParams(base: string, params: Record<string, string | number | null | undefined>): string {
  const u = new URLSearchParams();
  for (const [k, v] of Object.entries(params)) if (v !== undefined && v !== null && v !== '') u.set(k, String(v));
  const qs = u.toString();
  return qs ? `${base}?${qs}` : base;
}