IPRIT/test.ts

## test.ts
type CapitalLetters =
  | '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'

export type ToCamel<S extends string | number | symbol> = S extends string
  ? S extends `${infer Head}_${infer Tail}`
    ? Head extends ''
      ? Tail extends ''
        ? '_'
        : Tail extends `_${infer CAPS}`
        ? `_${Capitalize<ToCamel<CAPS>>}`
        : `${Capitalize<ToCamel<Tail>>}`
      : Tail extends `_${infer CAPS}`
      ? CAPS extends ''
        ? `${Uncapitalize<Head>}__`
        : `${Uncapitalize<Head>}_${Capitalize<ToCamel<CAPS>>}`
      : `${Uncapitalize<Head>}${Capitalize<ToCamel<Tail>>}`
    : S
  : never

export type ToCamelSafe<S extends string | number | symbol> = S extends string
  ? ToSnake<ToCamel<S>> extends S
    ? ToCamel<S>
    : `$${S}`
  : never

export type UnwrapSafe<S extends string> = S extends `$${infer Body}` ? Body : S
export type ToSnakeSafe<S extends string | number | symbol> = S extends `$${infer Body}` ? `${Body}` : ToSnake<S>

export type ToSnake<S extends string | number | symbol> = S extends string
  ? S extends `${infer Head}${CapitalLetters}${infer Tail}` // string has a capital char somewhere
    ? Head extends '' // there is a capital char in the first position
      ? Tail extends ''
        ? `_${Lowercase<S>}` /*  'A' */
        : S extends `${infer Caps}${Tail}` // tail exists, has capital characters
        ? Caps extends CapitalLetters
          ? Tail extends CapitalLetters
            ? `_${Lowercase<Caps>}_${Lowercase<Tail>}` /* 'AB' */
            : Tail extends `${CapitalLetters}${string}`
            ? `${ToSnake<Caps>}_${ToSnake<Tail>}` /* first tail char is upper? 'ABcd' */
            : `${ToSnake<Caps>}${ToSnake<Tail>}` /* 'AbCD','AbcD',  */ /* TODO: if tail is only numbers, append without underscore */
          : never /* never reached, used for inference of caps */
        : never
      : Tail extends '' /* 'aB' 'abCD' 'ABCD' 'AB' */
      ? S extends `${Head}${infer Caps}`
        ? Caps extends CapitalLetters
          ? Head extends Lowercase<Head> /* 'abcD' */
            ? `${ToSnake<Head>}${ToSnake<Caps>}`
            : never /* stop union type forming */
          : never
        : never /* never reached, used for inference of caps */
      : S extends `${Head}${infer Caps}${Tail}` /* 'abCd' 'ABCD' 'AbCd' 'ABcD' */
      ? Caps extends CapitalLetters
        ? Head extends Lowercase<Head> /* is 'abCd' 'abCD' ? */
          ? Tail extends CapitalLetters /* is 'abCD' where Caps = 'C' */
            ? `${ToSnake<Head>}_${ToSnake<Caps>}_${Lowercase<Tail>}` /* aBCD Tail = 'D', Head = 'aB' */
            : Tail extends `${CapitalLetters}${string}` /* is 'aBCd' where Caps = 'B' */
            ? `${Head}_${ToSnake<Caps>}_${ToSnake<Tail>}` /* 'aBCd' => `${'a'}_${Lowercase<'B'>}_${ToSnake<'Cd'>}` */
            : `${ToSnake<Head>}_${Lowercase<Caps>}${ToSnake<Tail>}` /* 'aBcD' where Caps = 'B' tail starts as lowercase */
          : never
        : never
      : never
    : S /* 'abc'  */
  : never

export type ObjectToSnake<T extends unknown, SAFE extends boolean> = T extends undefined
  ? undefined
  : T extends null
  ? null
  : T extends Array<infer ArrayType>
  ? ArrayType extends Record<string, unknown>
    ? Array<ObjectToSnake<ArrayType, SAFE>>
    : Array<ArrayType>
  : T extends Buffer
  ? Buffer
  : {
      [K in keyof T as SAFE extends true ? ToSnakeSafe<K> : ToSnake<K>]: T[K] extends
        | Array<infer ArrayType>
        | undefined
        | null
        ? ArrayType extends Record<string, unknown>
          ? Array<ObjectToSnake<ArrayType, SAFE>>
          : Array<ArrayType>
        : T[K] extends Record<string, unknown> | undefined | null
        ? ObjectToSnake<T[K], SAFE>
        : T[K]
    }

export type ObjectToCamel<T extends unknown, SAFE extends boolean> = T extends undefined
  ? undefined
  : T extends null
  ? null
  : T extends Array<infer ArrayType>
  ? ArrayType extends Record<string, unknown>
    ? Array<ObjectToCamel<ArrayType, SAFE>>
    : Array<ArrayType>
  : T extends Buffer
  ? Buffer
  : {
      [K in keyof T as SAFE extends true ? ToCamelSafe<K> : ToCamel<K>]: T[K] extends Array<infer ArrayType>
        ? ArrayType extends Record<string, unknown>
          ? Array<ObjectToCamel<ArrayType, SAFE>>
          : Array<ArrayType>
        : T[K] extends Record<string, unknown>
        ? ObjectToCamel<T[K], SAFE>
        : T[K]
    }
	type CapitalLetters =
	\| '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'

	export type ToCamel<S extends string \| number \| symbol> = S extends string
	? S extends `${infer Head}_${infer Tail}`
	? Head extends ''
	? Tail extends ''
	? '_'
	: Tail extends `_${infer CAPS}`
	? `_${Capitalize<ToCamel<CAPS>>}`
	: `${Capitalize<ToCamel<Tail>>}`
	: Tail extends `_${infer CAPS}`
	? CAPS extends ''
	? `${Uncapitalize<Head>}__`
	: `${Uncapitalize<Head>}_${Capitalize<ToCamel<CAPS>>}`
	: `${Uncapitalize<Head>}${Capitalize<ToCamel<Tail>>}`
	: S
	: never

	export type ToCamelSafe<S extends string \| number \| symbol> = S extends string
	? ToSnake<ToCamel<S>> extends S
	? ToCamel<S>
	: `$${S}`
	: never

	export type UnwrapSafe<S extends string> = S extends `$${infer Body}` ? Body : S
	export type ToSnakeSafe<S extends string \| number \| symbol> = S extends `$${infer Body}` ? `${Body}` : ToSnake<S>

	export type ToSnake<S extends string \| number \| symbol> = S extends string
	? S extends `${infer Head}${CapitalLetters}${infer Tail}` // string has a capital char somewhere
	? Head extends '' // there is a capital char in the first position
	? Tail extends ''
	? `_${Lowercase<S>}` /* 'A' */
	: S extends `${infer Caps}${Tail}` // tail exists, has capital characters
	? Caps extends CapitalLetters
	? Tail extends CapitalLetters
	? `_${Lowercase<Caps>}_${Lowercase<Tail>}` /* 'AB' */
	: Tail extends `${CapitalLetters}${string}`
	? `${ToSnake<Caps>}_${ToSnake<Tail>}` /* first tail char is upper? 'ABcd' */
	: `${ToSnake<Caps>}${ToSnake<Tail>}` /* 'AbCD','AbcD', / / TODO: if tail is only numbers, append without underscore */
	: never /* never reached, used for inference of caps */
	: never
	: Tail extends '' /* 'aB' 'abCD' 'ABCD' 'AB' */
	? S extends `${Head}${infer Caps}`
	? Caps extends CapitalLetters
	? Head extends Lowercase<Head> /* 'abcD' */
	? `${ToSnake<Head>}${ToSnake<Caps>}`
	: never /* stop union type forming */
	: never
	: never /* never reached, used for inference of caps */
	: S extends `${Head}${infer Caps}${Tail}` /* 'abCd' 'ABCD' 'AbCd' 'ABcD' */
	? Caps extends CapitalLetters
	? Head extends Lowercase<Head> /* is 'abCd' 'abCD' ? */
	? Tail extends CapitalLetters /* is 'abCD' where Caps = 'C' */
	? `${ToSnake<Head>}_${ToSnake<Caps>}_${Lowercase<Tail>}` /* aBCD Tail = 'D', Head = 'aB' */
	: Tail extends `${CapitalLetters}${string}` /* is 'aBCd' where Caps = 'B' */
	? `${Head}_${ToSnake<Caps>}_${ToSnake<Tail>}` /* 'aBCd' => `${'a'}_${Lowercase<'B'>}_${ToSnake<'Cd'>}` */
	: `${ToSnake<Head>}_${Lowercase<Caps>}${ToSnake<Tail>}` /* 'aBcD' where Caps = 'B' tail starts as lowercase */
	: never
	: never
	: never
	: S /* 'abc' */
	: never

	export type ObjectToSnake<T extends unknown, SAFE extends boolean> = T extends undefined
	? undefined
	: T extends null
	? null
	: T extends Array<infer ArrayType>
	? ArrayType extends Record<string, unknown>
	? Array<ObjectToSnake<ArrayType, SAFE>>
	: Array<ArrayType>
	: T extends Buffer
	? Buffer
	: {
	[K in keyof T as SAFE extends true ? ToSnakeSafe<K> : ToSnake<K>]: T[K] extends
	\| Array<infer ArrayType>
	\| undefined
	\| null
	? ArrayType extends Record<string, unknown>
	? Array<ObjectToSnake<ArrayType, SAFE>>
	: Array<ArrayType>
	: T[K] extends Record<string, unknown> \| undefined \| null
	? ObjectToSnake<T[K], SAFE>
	: T[K]
	}

	export type ObjectToCamel<T extends unknown, SAFE extends boolean> = T extends undefined
	? undefined
	: T extends null
	? null
	: T extends Array<infer ArrayType>
	? ArrayType extends Record<string, unknown>
	? Array<ObjectToCamel<ArrayType, SAFE>>
	: Array<ArrayType>
	: T extends Buffer
	? Buffer
	: {
	[K in keyof T as SAFE extends true ? ToCamelSafe<K> : ToCamel<K>]: T[K] extends Array<infer ArrayType>
	? ArrayType extends Record<string, unknown>
	? Array<ObjectToCamel<ArrayType, SAFE>>
	: Array<ArrayType>
	: T[K] extends Record<string, unknown>
	? ObjectToCamel<T[K], SAFE>
	: T[K]
	}