[Compose] Ex. FP-Box Chain

const Box = x =>
({
  map: f => Box(f(x)),
  chain: f => f(x),
  fold: f => f(x),
  toString: () => `Box(${x})`
})

// Exercise: Box
// Goal: Refactor each example using Box
// Keep these tests passing!
// Bonus points: no curly braces




// Ex1: Using Box, refactor moneyToFloat to be unnested.
// =========================
const _moneyToFloat = str =>
  parseFloat(str.replace(/$/, ''))
const moneyToFloat = str => Box(str)
    .map(str => str.replace(/$/, ''))
    .fold(parseFloat)

QUnit.test("Ex1: moneyToFloat", assert => {
  assert.equal(String(moneyToFloat('$5.00')), 5)
})





// Ex2: Using Box, refactor percentToFloat to remove assignment
// =========================
const _percentToFloat = str => {
  const float = parseFloat(str.replace(/\%/, ''))
  return float * 0.0100
}

const percentToFloat = str => Box(str)
    .map(str => str.replace(/\%/, ''))
    .map(parseFloat)
    .fold(float => float * 0.0100)


QUnit.test("Ex2: percentToFloat", assert => {
  assert.equal(String(percentToFloat('20%')), 0.2)
})





// Ex3: Using Box, refactor applyDiscount (hint: each variable introduces a new Box)
// =========================
const __applyDiscount = (price, discount) => {
  const cents = moneyToFloat(price)
  const savings = percentToFloat(discount)
  return cents - (cents * savings)
}

const _applyDiscount = (price, discount) => 
            Box(moneyToFloat(price))
             .fold(cents => Box(percentToFloat(discount))
            .fold(savings => cents - (cents * savings)))

const applyDiscount = (price, discount) => 
            Box(moneyToFloat(price))
             .chain(cents => Box(percentToFloat(discount))
            .fold(savings => cents - (cents * savings)))

QUnit.test("Ex3: Apply discount", assert => {
  assert.equal(String(applyDiscount('$5.00', '20%')), 4)
})