114-camelcase.ts

/**
 * 114 - CamelCase
 *
 * Implement `CamelCase<T>` which converts `snake_case` string to `camelCase`.
 *
 * For example
 *
 * ```ts
 * type camelCase1 = CamelCase<'hello_world_with_types'> // expected to be 'helloWorldWithTypes'
 * type camelCase2 = CamelCase<'HELLO_WORLD_WITH_TYPES'> // expected to be same as previous one
 * ```
 *
 *
 * <!--info-footer-start--><br><a href="../../README.md" target="_blank"><img src="https://img.shields.io/badge/-Back-grey" alt="Back"/></a> <a href="https://tsch.js.org/114/answer" target="_blank"><img src="https://img.shields.io/badge/-Share%20your%20Solutions-teal" alt="Share your Solutions"/></a> <a href="https://tsch.js.org/114/solutions" target="_blank"><img src="https://img.shields.io/badge/-Check%20out%20Solutions-de5a77?logo=awesome-lists&logoColor=white" alt="Check out Solutions"/></a> <hr><h3>Related Challenges</h3><a href="https://github.com/type-challenges/type-challenges/blob/main/questions/00612-medium-kebabcase/README.md" target="_blank"><img src="https://img.shields.io/badge/-612%E3%83%BBKebabCase-d9901a" alt="612・KebabCase"/></a> <!--info-footer-end-->
 */

/* _____________ Your Code Here _____________ */

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

type CamelCase<S extends string> = S extends `${infer Left}_${infer Right}${infer Rest}`
  ? IsLetter<Right> extends true
    ? `${Lowercase<Left>}${Uppercase<Right>}${CamelCase<Rest>}`
    : `${Left}_${CamelCase<`${Right}${Rest}`>}`
  : Lowercase<S>

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<CamelCase<'foobar'>, 'foobar'>>,
  Expect<Equal<CamelCase<'FOOBAR'>, 'foobar'>>,
  Expect<Equal<CamelCase<'foo_bar'>, 'fooBar'>>,
  Expect<Equal<CamelCase<'foo__bar'>, 'foo_Bar'>>,
  Expect<Equal<CamelCase<'foo_$bar'>, 'foo_$bar'>>,
  Expect<Equal<CamelCase<'foo_bar_'>, 'fooBar_'>>,
  Expect<Equal<CamelCase<'foo_bar__'>, 'fooBar__'>>,
  Expect<Equal<CamelCase<'foo_bar_$'>, 'fooBar_$'>>,
  Expect<Equal<CamelCase<'foo_bar_hello_world'>, 'fooBarHelloWorld'>>,
  Expect<Equal<CamelCase<'HELLO_WORLD_WITH_TYPES'>, 'helloWorldWithTypes'>>,
  Expect<Equal<CamelCase<'-'>, '-'>>,
  Expect<Equal<CamelCase<''>, ''>>,
  Expect<Equal<CamelCase<'😎'>, '😎'>>,
]