/**
 * Class-name composer — the kit's local replacement for `clsx`.
 *
 * It flattens strings, numbers, arrays and `{ class: condition }` objects into
 * one space-separated string, dropping anything falsy. It does **not** resolve
 * Tailwind conflicts; that is `twMerge`'s job and happens in `cn()`.
 *
 * ```ts
 * cx('px-2', isActive && 'bg-accent', { 'opacity-50': disabled }, ['a', 'b'])
 * ```
 */

export type ClassDictionary = Record<string, unknown>;
export type ClassArray = ClassValue[];
export type ClassValue =
  | ClassArray
  | ClassDictionary
  | string
  | number
  | bigint
  | null
  | boolean
  | undefined;

/** Joins with a single space, without leaving a leading one on the first item. */
const join = (accumulated: string, next: string) =>
  accumulated ? `${accumulated} ${next}` : next;

function flatten(value: ClassValue): string {
  if (typeof value === 'string') return value;
  if (typeof value === 'number' || typeof value === 'bigint') return String(value);
  /* Booleans, null and undefined carry no class name. Guarding here is what
     makes `cond && 'cls'` work without the caller filtering first. */
  if (typeof value !== 'object' || value === null) return '';

  let out = '';

  if (Array.isArray(value)) {
    for (const item of value) {
      if (!item) continue;
      const resolved = flatten(item);
      if (resolved) out = join(out, resolved);
    }
    return out;
  }

  /* Object form: the key is the class, the value is the condition. */
  for (const key in value) {
    if (value[key]) out = join(out, key);
  }
  return out;
}

export function cx(...inputs: ClassValue[]): string {
  let out = '';
  for (const input of inputs) {
    if (!input) continue;
    const resolved = flatten(input);
    if (resolved) out = join(out, resolved);
  }
  return out;
}