// [K in keyof T]: 타입 T의 모든 키를 순회
type MyReadonly<T> = {
  readonly [K in keyof T]: T[K]
}

type MyPartial<T> = {
  [K in keyof T]?: T[K]
}

type MyRequired<T> = {
  [K in keyof T]-?: T[K]  // ? 제거 (Required)
}

// 모든 값을 string으로
type Stringify<T> = {
  [K in keyof T]: string
}

// 모든 값을 배열로
type Arrayify<T> = {
  [K in keyof T]: T[K][]
}

interface Point { x: number; y: number }

type StringPoint = Stringify<Point>  // { x: string; y: string }
type ArrayPoint  = Arrayify<Point>   // { x: number[]; y: number[] }

// 모든 키에 get 접두사 추가
type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
}

interface User { name: string; age: number }

type UserGetters = Getters<User>
// {
//   getName: () => string
//   getAge:  () => number
// }

// string 값만 가진 키 추출
type StringKeys<T> = {
  [K in keyof T]: T[K] extends string ? K : never
}[keyof T]

interface Mixed {
  id: number
  name: string
  email: string
  active: boolean
}

type StrKeys = StringKeys<Mixed>  // 'name' | 'email'

// 활용: 문자열 필드만 있는 타입
type StringFields<T> = Pick<T, StringKeys<T>>
type MixedStrings = StringFields<Mixed>  // { name: string; email: string }

// 이벤트 맵에서 on-핸들러 타입 자동 생성
type EventHandlers<T extends Record<string, any>> = {
  [K in keyof T as `on${Capitalize<string & K>}`]?: (event: T[K]) => void
}

interface AppEvents {
  click:  { x: number; y: number }
  submit: { formData: FormData }
  resize: { width: number; height: number }
}

type Handlers = EventHandlers<AppEvents>
// {
//   onClick?:  (event: { x: number; y: number }) => void
//   onSubmit?: (event: { formData: FormData }) => void
//   onResize?: (event: { width: number; height: number }) => void
// }

type FormState<T> = {
  values: T
  errors: Partial<Record<keyof T, string>>
  touched: Partial<Record<keyof T, boolean>>
  dirty: boolean
  isSubmitting: boolean
}

interface LoginForm {
  email: string
  password: string
}

type LoginFormState = FormState<LoginForm>
// values.email, errors.email, touched.email 등이 모두 타입 안전

type DeepReadonly<T> = {
  readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K]
}

const config: DeepReadonly<{ db: { host: string; port: number } }> = {
  db: { host: 'localhost', port: 5432 }
}

config.db.host = 'prod'  // ❌ 깊은 곳까지 읽기 전용