//Bad case
const init: number = 0

const add = (number: number) => {
  return number + init
}

add(5)

//Good case
const init: number = 0

const add = (number: number, init: number = 0) => {
  return number + init
}

add(5)

//Bad Case
const fruits: string[] = ['Apple', 'Orange', 'Blueberry']

const head = (arr: string[]) => {
  return arr.shift()
}

console.log(head(fruits))

//Good Case
const fruits: string[] = ['Apple', 'Orange', 'Blueberry']

const head = (arr: string[]) => {
  return arr.length < 1 ? undefined : arr[0]
}

console.log(head(fruits))

//Bad Case
const fruits: string[] = ['Apple', 'Orange', 'Blueberry']
fruits[2] = 'Tomato'

//Good Case
const fruits: string[] = ['Apple', 'Orange', 'Blueberry']

const newFruits = fruits.map((fruit: string) =>
  fruit === 'Blueberry' ? 'Tomato' : fruit
)

console.log('newFruites = ', newFruits)

const arr: number[] = [1, 2, 3, 4, 5]

// 1. 홀수만 걸러주세요
// 2. 걸러진 원소에 곱하기 2를 해주세요
// 3. 모두 다 더해주세요

let sum = 0
for (const el of arr) {
  if (el % 2 === 1) {
    const newElement = el * 2
    sum += newElement
  }
}

const sum2 = arr
  .filter(el => el % 2 === 1)
  .map(el => el * 2)
  .reduce((prev, curr) => prev + curr)

/**
 * map: 배열을 순회하면서 func 을 적용해서 새로운 결과 값을 담은 배열을 리턴한다.
 * func: (el) => value
 */
const map = (func, iter) => {
  const result = []

  for (const el of iter) {
    result.push(func(el))
  }

  return result
}
console.log(map(el => el * 2, arr))

/**
 *  filter: 배열을 순회하면서 func 의 truthy 값(조건에 맞는 값)만 배열에 담아 리턴한다.
 *  func: (el) => truthy | falsy
 */
const filter = (func, iter) => {
  const result = []

  for (const el of iter) {
    if (func(el)) {
      result.push(el)
    }
  }

  return result
}

console.log(filter(el => el % 2 === 1, arr))

/**
 * reduce: 배열을 순회면서 func 을 반복 적용해서 새로운 결과 값을 얻어낸다. (쪼개는 함수)
 * func: (acc, el) => acc
 * func: (prev, curr) => acc
 */

const reduce = (func, acc, iter) => {
  if (iter === undefined) {
    iter = acc[Symbol.iterator]()
    acc = iter.next().value
  }

  for (const el of iter) {
    acc = func(acc, el)
  }

  return acc
}

console.log(reduce((prev, curr) => prev + curr, 0, arr))
console.log(reduce((prev, curr) => prev + curr, arr))

/**
 * 함수의 합성, pipe
 * 순회 가능한 객체를 받아서 함수의 파이프라인을 타고 최종 결과값을 리턴한다.
 */
const pipe = (iter, ...functions) =>
  reduce((prev, func) => func(prev), iter, functions)

const arr = [1, 2, 3, 4, 5]

const sum2 = arr
  .filter(el => el % 2 === 1)
  .map(el => el * 2)
  .reduce((prev, curr) => prev + curr)

console.log(sum2)

pipe(
  arr,
  arr => filter(el => el % 2 === 1, arr),
  arr => map(el => el * 2, arr),
  arr => reduce((prev, curr) => prev + curr, arr),
  result => console.log(result)
)

const curry = func => (a, ...args) =>
  args.length > 0 ? func(a, ...args) : (...args) => func(a, ...args)

const map = curry((func, iter) => {
  const result = []
  for (const el of iter) {
    result.push(func(el))
  }

  return result
})

const filter = curry((func, iter) => {
  const result = []
  for (const el of iter) {
    if (func(el)) {
      result.push(el)
    }
  }

  return result
})

const reduce = curry((func, acc, iter) => {
  if (iter === undefined) {
    iter = acc[Symbol.iterator]()
    acc = iter.next().value
  }

  for (const el of iter) {
    acc = func(acc, el)
  }

  return acc
})

const arr = [1, 2, 3, 4, 5]
const noCurAdd = (a, b) => a + b

console.log(noCurAdd(1, 3))
console.log(noCurAdd(1)) //포인트 1
console.log(noCurAdd(1)(3)) //에러 포인트

const curAdd = curry((a, b) => a + b)
console.log(curAdd(1, 3))
console.log(curAdd(1)) //포인트 2
console.log(curAdd(1)(3))

4
NaN
/Users/mhlab/Develop/study/Wanted/PreOnboard_Back/lecture/wanted-pre-onboarding-challenge-BE-task-JAN.2023/lecture-1/3.js:53
console.log(noCurAdd(1)(3)); //에러 포인트
                       ^

TypeError: noCurAdd(...) is not a function
    at Object.<anonymous> (/Users/mhlab/Develop/study/Wanted/PreOnboard_Back/lecture/wanted-pre-onboarding-challenge-BE-task-JAN.2023/lecture-1/3.js:53:24)
    at Module._compile (node:internal/modules/cjs/loader:1155:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1209:10)
    at Module.load (node:internal/modules/cjs/loader:1033:32)
    at Function.Module._load (node:internal/modules/cjs/loader:868:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:22:47

4
[Function (anonymous)]
4