00114-hard-camelcase.ts

// ============= Test Cases =============
import type { Equal, Expect } from './test-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<'😎'>, '😎'>>
];

// ============= Your Code Here =============
type Letters =
  | 'a'
  | 'b'
  | 'c'
  | 'd'
  | 'e'
  | 'f'
  | 'g'
  | 'h'
  | 'i'
  | 'j'
  | 'k'
  | 'l'
  | 'm'
  | 'n'
  | 'o'
  | 'p'
  | 'q'
  | 'r'
  | 's'
  | 't'
  | 'u'
  | 'v'
  | 'w'
  | 'x'
  | 'y'
  | 'z'
  | 'A'
  | 'B'
  | 'C'
  | 'D'
  | 'E'
  | 'F'
  | 'G'
  | 'H'
  | 'I'
  | 'J'
  | 'K'
  | 'L'
  | 'M'
  | 'N'
  | 'O'
  | 'P'
  | 'Q'
  | 'R'
  | 'S'
  | 'T'
  | 'U'
  | 'V'
  | 'W'
  | 'X'
  | 'Y'
  | 'Z';
type StartWithLetter<S extends string> = S extends `${infer _ extends Letters}${string}`
  ? true
  : false;
  
type CamelCase<S extends string> = S extends `${infer Word1}_${infer Word2}`
  ? StartWithLetter<Word2> extends true
    ? `${Lowercase<Word1>}${Capitalize<CamelCase<Word2>>}`
    : `${Lowercase<Word1>}_${Capitalize<CamelCase<Word2>>}`
  : Lowercase<S>;