cx (classNames)

// Tiny className joiner (isomorphic, no deps).
export type ClassValue =
  | string
  | number
  | null
  | false
  | undefined
  | Record<string, boolean | null | undefined>
  | ClassValue[];

export function cx(...parts: ClassValue[]): string {
  const out: string[] = [];
  for (const p of parts) {
    if (!p) continue;
    if (typeof p === "string" || typeof p === "number") out.push(String(p));
    else if (Array.isArray(p)) {
      const s = cx(...p);
      if (s) out.push(s);
    } else if (typeof p === "object") {
      for (const k in p) if (p[k]) out.push(k);
    }
  }
  return out.join(" ");
}