Swift Register Command LIne

CashRegister.swift

import Foundation

while let line: String = readLine() {
  print(processInput(line))
}

func processInput(_ line: String) -> String {
    let components = line.components(separatedBy: ";")
    guard components.count == 2,
        let price = Float(components[0]),
        let cash = Float(components[1]) else {
        return "Invalid input"
    }
    // input validation
    guard cash > price else {
        if cash == price {
            return "ZERO"
        } else {
            return "ERROR"
        }
    }
    let change = registerChange(price: price, cash: cash)
    assert(change.isEmpty == false)
    return change.reduce("", { $0 + ($0.isEmpty ? "" : ",") + $1.print })
}

func registerChange(price: Float, cash: Float) -> [Coin] {
    guard price != cash, price < cash else {
        return []
    }
    var changeValue = cash - price
    var coins = [Coin]()
    while let coin = largestDenomination(for: changeValue) {
        changeValue -= coin.rawValue
        coins.append(coin)
    }
    return coins
}

func largestDenomination(for change: Float) -> Coin? {
    Coin.allCases
        .sorted(by: { $0.rawValue > $1.rawValue })
        .first(where: { $0.rawValue <= change })
}

enum Coin: Float, CaseIterable {
  case penny      = 0.01
  case nickel     = 0.05
  case dime       = 0.10
  case quarter    = 0.25
  case half       = 0.50
  case one        = 1.00
  case two        = 2.00
  case five       = 5.00
  case ten        = 10.00
  case twenty     = 20.00
  case fifty      = 50.00
  case oneHundred = 100.00
}

private extension Coin {
    
    var print: String {
        switch self {
          case .penny: return "PENNY"
          case .nickel: return "NICKEL"
          case .dime: return "DIME"
          case .quarter: return "QUARTER"
          case .half: return "HALF DOLLAR"
          case .one: return "ONE"
          case .two: return "TWO"
          case .five: return "FIVE"
          case .ten: return "TEN"
          case .twenty: return "TWENTY"
          case .fifty: return "FIFTY"
          case .oneHundred: return "ONE HUNDRED"
        }
    }
}