type IsAlphabet<S extends string> = S extends Uppercase<S>
  ? S extends Lowercase<S>
    ? false
    : true
  : true;


type KebabCaseInner<S extends string> = S extends `${infer First}${infer Rest}`
  ? IsAlphabet<First> extends true
    ? First extends Uppercase<First>
      ? `-${Lowercase<First>}${KebabCaseInner<Rest>}`
      : `${First}${KebabCaseInner<Rest>}`
    : `${First}${KebabCaseInner<Rest>}`
  : '';

type KebabCase<S extends String> = S extends `${infer First}${infer Rest}`
  ? `${Lowercase<First>}${KebabCaseInner<Rest>}`
  : '';

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<KebabCase<'FooBarBaz'>, 'foo-bar-baz'>>,
  Expect<Equal<KebabCase<'fooBarBaz'>, 'foo-bar-baz'>>,
  Expect<Equal<KebabCase<'foo-bar'>, 'foo-bar'>>,
  Expect<Equal<KebabCase<'foo_bar'>, 'foo_bar'>>,
  Expect<Equal<KebabCase<'Foo-Bar'>, 'foo--bar'>>,
  Expect<Equal<KebabCase<'ABC'>, 'a-b-c'>>,
  Expect<Equal<KebabCase<'-'>, '-'>>,
  Expect<Equal<KebabCase<''>, ''>>,
  Expect<Equal<KebabCase<'😎'>, '😎'>>,
]