money-currency-types.swift

//: Types for currency conversion
// https://www.natashatherobot.com/swift-money-phantom-types/

import Foundation


struct Money {
	enum Currency {
		case GBP, EUR, USD
	}
	
	let amount: NSDecimalNumber
	let currency: Currency
}


extension Money.Currency {
	var singleInEUR: NSDecimalNumber {
		// From http://www.xe.com/currencycharts
		switch self {
		case .GBP:
			return NSDecimalNumber(mantissa: 126816, exponent: -5, isNegative: false)
		case .EUR:
			return NSDecimalNumber(integer: 1)
		case .USD:
			return NSDecimalNumber(mantissa: 88203, exponent: -5, isNegative: false)
		}
	}
}

extension Money {
	func convertedToCurrency(currency: Currency) -> Money {
		let amountInEUR = amount.decimalNumberByMultiplyingBy(self.currency.singleInEUR)
		let convertedAmount = amountInEUR.decimalNumberByDividingBy(currency.singleInEUR)
		return Money(amount: convertedAmount, currency: currency)
	}
}

extension Money: CustomStringConvertible {
	var description: String {
		return "\(amount) \(currency)"
	}
}

let fivePounds = Money(amount: 5, currency: .GBP)
let threeEuros = Money(amount: 3, currency: .EUR)
let eightDollars = Money(amount: 8, currency: .USD)

let fivePoundsInEuros = fivePounds.convertedToCurrency(.EUR)
let fivePoundsInUSD = fivePounds.convertedToCurrency(.USD)
let eightDollarsInPounds = eightDollars.convertedToCurrency(.GBP)