USD's Buying Power vs. 1 Year Ago

currencies.rb

# Ruby code to print the US dollar relative buying power vs 1 year ago at various popular travel destinations

CURRENCY_API_KEY = "get one for free at https://apilayer.com/marketplace/exchangerates_data-api?live_demo=show"

def self.currency_report
  # using a public exchange rate API, get the historic rate vs. today's and compute the % change.
  # List currencies of popular travel destinations
  currencies = [
    {code: "JPY", name: "Japanese Yen"},
    {code: "EUR", name: "Euro"},
    {code: "MXN", name: "Mexican Peso"},
    {code: "CAD", name: "Canadian Dollar"},
    {code: "GBP", name: "British Pound"},
    {code: "AUD", name: "Australian Dollar"},
    {code: "NZD", name: "New Zealand Dollar"},
    {code: "BRL", name: "Brazilian Real"},
    {code: "ZAR", name: "South African Rand"},
    {code: "KRW", name: "South Korean Won"},
    {code: "THB", name: "Thai Baht"},
    {code: "VND", name: "Vietnamese Dollar"},
    {code: "TRY", name: "Turkish Lira"},
    {code: "SAR", name: "Saudi Riyal"},
    {code: "EGP", name: "Egyptian Pound"},
    {code: "ILS", name: "Israeli Shekel"},
    {code: "ARS", name: "Argentine Peso"},
    {code: "SEK", name: "Swedish Krona"},
    {code: "HKD", name: "Hong Kong Dollar"},
    {code: "SGD", name: "Singapore Dollar"},
    {code: "ISK", name: "Icelandic Krona"},
  ]

  changes = []
  currencies.each do |currency|
    # get the exchange rate for today
    today = get_exchange_rate(currency[:code]).to_f
    # get the exchange rate for 1 year ago
    year_ago = get_exchange_rate(currency[:code], 1.year.ago).to_f

    # To purchase a year ago's worth of currency, how much would you have to pay today as a % discount?
    # 1 year ago, $1 bought 114.5 yen
    # today, $1 buys 149.8
    # therefore, to buy 114.5 yen today, you only need to pay 114.5/149.8 = $0.76
    needed_today = year_ago / today

    # the % discount of needed_today vs 1.0 is the % change:
    change = (1.0 - needed_today) * 100
    # format like %:
    change_str = change.round(1).to_s + "%"
    changes << {name: currency[:name], change: change, change_str: change_str}
  end

  # sort by changes[:change] desc:
  changes.sort_by! {|c| c[:change]}.reverse!

  # print report
  changes.each do |change|
    discount_or_premium = change[:change] > 0 ? "discount" : "premium"
    puts "The #{change[:name]} feels like a #{change[:change_str]} #{discount_or_premium} vs. a year ago.".white.bold
  end
end

def self.get_exchange_rate(currency_code, time_ago = Time.current)
  api_key = CURRENCY_API_KEY

  # format time_ago as yyyy-mm-dd
  date_str = time_ago.strftime("%Y-%m-%d")
  url = URI("https://api.apilayer.com/exchangerates_data/#{date_str}?symbols=#{currency_code}&base=USD")

  https = Net::HTTP.new(url.host, url.port);
  https.use_ssl = true

  request = Net::HTTP::Get.new(url)
  request['apikey'] = api_key

  response = https.request(request)
  data = JSON.parse(response.read_body)
  return data["rates"][currency_code]
end

It's a good time for Americans to travel overseas!