TS snake case to camel case

TS_cases.ts

// Original author is ford04 (https://stackoverflow.com/users/5669456/ford04)
// Original answer on stack overflow (https://stackoverflow.com/questions/60269936/typescript-convert-generic-object-from-snake-to-camel-case)
type SnakeToCamelCase<S extends string> =
  S extends `${infer T}_${infer U}` ?
  `${T}${Capitalize<SnakeToCamelCase<U>>}` :
  S

type CamelToSnakeCase<S extends string> =
  S extends `${infer T}${infer U}` ?
  `${T extends Capitalize<T> ? "_" : ""}${Lowercase<T>}${CamelToSnakeCase<U>}` :
  S

type CamelToPascalCase<S extends string> = Capitalize<S>
type PascalToCamelCase<S extends string> = Uncapitalize<S>
type PascalToSnakeCase<S extends string> = CamelToSnakeCase<Uncapitalize<S>>
type SnakeToPascalCase<S extends string> = Capitalize<SnakeToCamelCase<S>>

type T11 = SnakeToCamelCase<"hello"> // "hello"
type T12 = SnakeToCamelCase<"hello_world"> // "helloWorld"
type T13 = SnakeToCamelCase<"hello_ts_world"> // "helloTsWorld"
type T14 = SnakeToCamelCase<"hello_world" | "foo_bar"> // "helloWorld" | "fooBar"
type T15 = SnakeToCamelCase<string> // string
type N = 42
type T16 = SnakeToCamelCase<`the_answer_is_${N}`> // "theAnswerIs42" (type N = 42)

type T21 = CamelToSnakeCase<"hello"> // "hello"
type T22 = CamelToSnakeCase<"helloWorld"> // "hello_world"
type T23 = CamelToSnakeCase<"helloTsWorld"> // "hello_ts_world"

type T31 = CamelToPascalCase<"hello">
type T32 = CamelToPascalCase<"helloWorld">
type T33 = CamelToPascalCase<"helloTsWorld">

type T41 = SnakeToPascalCase<"hello">
type T42 = SnakeToPascalCase<"hello_world">
type T43 = SnakeToPascalCase<"hello_ts_world">

type T51 = PascalToCamelCase<"Hello">
type T52 = PascalToCamelCase<"HelloWorld">
type T53 = PascalToCamelCase<"HelloTsWorld">

type T61 = PascalToSnakeCase<"Hello">
type T62 = PascalToSnakeCase<"HelloWorld">
type T63 = PascalToSnakeCase<"HelloTsWorld">

type InputType = {
  snake_case_key_1: number,
  snake_case_key_2: string,
}

type OutputType = { [K in keyof InputType as SnakeToCamelCase<K>]: InputType[K] }
/*
  type OutputType = {
      snakeCaseKey1: number;
      snakeCaseKey2: string;
  }
*/

/**
 * 
 * Extension: Convert nested properties
 * 
 */
type InputTypeNested = {
  snake_case_key_1: {
    snake_case_key_11: string
    snake_case_key_12: string
  },
  snake_case_key_2: string,
}

type SnakeToCamelCaseNested<T> = T extends object ? {
  [K in keyof T as SnakeToCamelCase<K & string>]: SnakeToCamelCaseNested<T[K]>
} : T

type OutputTypeNested = SnakeToCamelCaseNested<InputTypeNested>